/ [, …] [param*]

Define one or several listening addresses and/or ports in a frontend.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<address>     is optional and can be a host name, an IPv4 address, an IPv6
              address, or '*'. It designates the address the frontend will
              listen on. If unset, all IPv4 addresses of the system will be
              listened on. The same will apply for '*' or the system's
              special address "0.0.0.0". The IPv6 equivalent is '::'.
              Optionally, an address family prefix may be used before the
              address to force the family regardless of the address format,
              which can be useful to specify a path to a unix socket with
              no slash ('/'). Currently supported prefixes are :
                - 'ipv4@'  -> address is always IPv4
                - 'ipv6@'  -> address is always IPv6
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only).
                  Note: since abstract sockets are not "rebindable", they
                        do not cope well with multi-process mode during
                        soft-restart, so it is better to avoid them if
                        nbproc is greater than 1. The effect is that if the
                        new process fails to start, only one of the old ones
                        will be able to rebind to the socket.
                - 'fd@<n>' -> use file descriptor <n> inherited from the
                  parent. The fd must be bound and may or may not already
                  be listening.
                - 'sockpair@<n>'-> like fd@ but you must use the fd of a
                  connected unix socket or of a socketpair. The bind waits
                  to receive a FD over the unix socket and uses it as if it
                  was the FD of an accept(). Should be used carefully.
              You may want to reference some environment variables in the
              address parameter, see section 2.3 about environment
              variables.
 
<port_range>  is either a unique TCP port, or a port range for which the
              proxy will accept connections for the IP address specified
              above. The port is mandatory for TCP listeners. Note that in
              the case of an IPv6 address, the port is always the number
              after the last colon (':'). A range can either be :
               - a numerical port (ex: '80')
               - a dash-delimited ports range explicitly stating the lower
                 and upper bounds (ex: '2000-2100') which are included in
                 the range.
 
              Particular care must be taken against port ranges, because
              every <address:port> couple consumes one socket (= a file
              descriptor), so it's easy to consume lots of descriptors
              with a simple range, and to run out of sockets. Also, each
              <address:port> couple must be used only once among all
              instances running on a same system. Please note that binding
              to ports lower than 1024 generally require particular
              privileges to start the program, which are independent of
              the 'uid' parameter.
 
<path>        is a UNIX socket path beginning with a slash ('/'). This is
              alternative to the TCP listening port. HAProxy will then
              receive UNIX connections on the socket located at this place.
              The path must begin with a slash and by default is absolute.
              It can be relative to the prefix defined by "" in
              the global section. Note that the total length of the prefix
              followed by the socket path cannot exceed some system limits
              for UNIX sockets, which commonly are set to 107 characters.
 
<param*>      is a list of parameters common to all sockets declared on the
              same line. These numerous parameters depend on OS and build
              options and have a complete section dedicated to them. Please
              refer to section 5 to for more details.

It is possible to specify a list of address:port combinations delimited by
commas. The frontend will then listen on all of these addresses. There is no
fixed limit to the number of addresses and ports which can be listened on in
a frontend, as well as there is no limit to the number of "
This keyword is available in sections :
Peers
" statements
in a frontend.

Example :

listen http_proxy
    bind :80,:443
    bind 10.0.0.1:10080,10.0.0.1:10443
    bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy
listen http_https_proxy
    bind :80
    bind :443 ssl crt /etc/haproxy/site.pem
listen http_https_proxy_explicit
    bind ipv6@:80
    bind ipv4@public_ssl:443 ssl crt /etc/haproxy/site.pem
    bind unix@ssl-frontend.sock user root mode 600 accept-proxy
listen external_bind_app1
    bind "fd@${FD_APP1}"

Note: regarding Linux's abstract namespace sockets, HAProxy uses the whole
      sun_path length is used for the address length. Some other programs
      such as socat use the string length only by default. Pass the option
      ",unix-tightsocklen=0" to any abstract socket definition in socat to
      make it compatible with HAProxy's.

See also : “source

• This keyword is available in sections :
• Server and default-server options

“, ““, “unix-bind“ and the PROXY protocol documentation, and about bind options.

bind-process [ all | odd | even | [-[]] ] …

Limit visibility of an instance to a certain set of processes numbers.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

all           All process will see this instance. This is the default. It
              may be used to override a default value.
 
odd           This instance will be enabled on processes 1,3,5,...63. This
              option may be combined with other numbers.
 
even          This instance will be enabled on processes 2,4,6,...64. This
              option may be combined with other numbers. Do not use it
              with less than 2 processes otherwise some instances might be
              missing from all processes.
 
process_num   The instance will be enabled on this process number or range,
              whose values must all be between 1 and 32 or 64 depending on
              the machine's word size. Ranges can be partially defined. The
              higher bound can be omitted. In such case, it is replaced by
              the corresponding maximum value. If a proxy is bound to
              process numbers greater than the configured global.nbproc, it
              will either be forced to process #1 if a single process was
              specified, or to all processes otherwise.

This keyword limits binding of certain instances to certain processes. This
is useful in order not to have too many processes listening to the same
ports. For instance, on a dual-core machine, it might make sense to set
'nbproc 2' in the global section, then distributes the listeners among 'odd'
and 'even' instances.
 
At the moment, it is not possible to reference more than 32 or 64 processes
using this keyword, but this should be more than enough for most setups.
Please note that 'all' really means all processes regardless of the machine's
word size, and is not limited to the first 32 or 64.
 
Each "
This keyword is available in sections :
Peers
" line may further be limited to a subset of the proxy's processes,
please consult the "process" bind keyword in .
 
When a frontend has no explicit "bind-process" line, it tries to bind to all
the processes referenced by its "
This keyword is available in sections :
Peers
" lines. That means that frontends can
easily adapt to their listeners' processes.
 
If some backends are referenced by frontends bound to other processes, the
backend automatically inherits the frontend's processes.

Example :

listen app_ip1
    bind 10.0.0.1:80
    bind-process odd
listen app_ip2
    bind 10.0.0.2:80
    bind-process even
listen management
    bind 10.0.0.3:80
    bind-process 1 2 3 4
listen management
    bind 10.0.0.4:80
    bind-process 1-4

See also : “nbproc

• This keyword is available in sections :
• Fetching samples from internal states

“ in global section, and ““ in section 5.1.

{ if | unless } (deprecated)

Block a layer 7 request if/unless a condition is matched

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

The HTTP request will be blocked very early in the layer 7 processing
if/unless <condition> is matched. A 403 error will be returned if the request
is blocked. The condition has to reference ACLs (see section 7). This is
typically used to deny access to certain sensitive resources if some
conditions are met or not met. There is no fixed limit to the number of
"" statements per instance. To block connections at layer 4 (without
sending a 403 error) see "tcp-request connection reject" and
"tcp-request content reject" rules.
 
This form is deprecated, do not use it in any new configuration, use the new
"http-request deny" instead.

Example:

acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
acl invalid_src  src_port     0:1023
acl local_dst    hdr(host) -i localhost
# block is deprecated. Use http-request deny instead:
#block if invalid_src || local_dst
http-request deny if invalid_src || local_dst

See also : about ACL usage, “http-request deny“, ““, “tcp-request connection reject” and “tcp-request content reject”.

capture cookie len

Capture and log a cookie in the request and in the response.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<name>    is the beginning of the name of the cookie to capture. In order
          to match the exact name, simply suffix the name with an equal
          sign ('='). The full name will appear in the logs, which is
          useful with application servers which adjust both the cookie name
          and value (e.g. ASPSESSIONXXX).
 
<length>  is the maximum number of characters to report in the logs, which
          include the cookie name, the equal sign and the value, all in the
          standard "name=value" form. The string will be truncated on the
          right if it exceeds <length>.

Only the first cookie is captured. Both the "
This keyword is available in sections :
Alphabetically sorted keywords reference
Fetching HTTP samples (Layer 7)
" request headers and the
"" response headers are monitored. This is particularly useful to
check for application bugs causing session crossing or stealing between
users, because generally the user's cookies can only change on a login page.
 
When the cookie was not presented by the client, the associated log column
will report "-". When a request does not cause a cookie to be assigned by the
server, a "-" is reported in the response column.
 
The capture is performed in the frontend only because it is necessary that
the log format does not change for a given frontend depending on the
backends. This may change in the future. Note that there can be only one
"capture cookie" statement in a frontend. The maximum capture length is set
by the global "" setting and defaults to 63 characters. It
is not possible to specify a capture in a "defaults" section.

Example:

capture cookie ASPSESSION len 32

See also : “capture request header“, ““ as well as section 8 about logging.

len

Capture and log the last occurrence of the specified request header.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the requests, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.
 
<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.

The complete value of the last occurrence of the header is captured. The
value will be added to the logs between braces ('{}'). If multiple headers
are captured, they will be delimited by a vertical bar ('|') and will appear
in the same order they were declared in the configuration. Non-existent
headers will be logged just as an empty string. Common uses for request
header captures include the "Host" field in virtual hosting environments, the
"Content-length" when uploads are supported, "User-agent" to quickly
differentiate between real users and robots, and "X-Forwarded-For" in proxied
environments to find where the request came from.
 
Note that when capturing headers such as "User-agent", some spaces may be
logged, making the log analysis more difficult. Thus be careful about what
you log if you know your log parser is not smart enough to rely on the
braces.
 
There is no limit to the number of captured request headers nor to their
length, though it is wise to keep them low to limit memory usage per session.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.

Example:

capture request header Host len 15
capture request header X-Forwarded-For len 15
capture request header Referer len 15

See also : “capture cookie“, ““ as well as section 8 about logging.

len

Capture and log the last occurrence of the specified response header.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the response, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.
 
<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.

The complete value of the last occurrence of the header is captured. The
result will be added to the logs between braces ('{}') after the captured
request headers. If multiple headers are captured, they will be delimited by
a vertical bar ('|') and will appear in the same order they were declared in
the configuration. Non-existent headers will be logged just as an empty
string. Common uses for response header captures include the "Content-length"
header which indicates how many bytes are expected to be returned, the
"Location" header to track redirections.
 
There is no limit to the number of captured response headers nor to their
length, though it is wise to keep them low to limit memory usage per session.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.

Example:

capture response header Content-length len 9
capture response header Location len 15

See also : “capture cookie“, ““ as well as section 8 about logging.

(deprecated)

Set the maximum inactivity time on the client side.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<timeout> is the timeout value is specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the client is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase, when the client sends the request, and during the
response while it is reading data sent by the server. The value is specified
in milliseconds by default, but can be in any other unit if the number is
suffixed by the unit, as specified at the top of this document. In TCP mode
(and to a lesser extent, in HTTP mode), it is highly recommended that the
client timeout remains equal to the server timeout in order to avoid complex
situations to debug. It is a good practice to cover one or several TCP packet
losses by specifying timeouts that are slightly above multiples of 3 seconds
(e.g. 4 or 5 seconds).
 
This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of expired sessions in
the system if the system's timeouts are not configured either.
 
This parameter is provided for compatibility but is currently deprecated.
Please use "timeout client" instead.

See also : ““, “timeout http-request“, ““, and “srvtimeout“.

…

compression type …

Enable HTTP compression.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

algo     is followed by the list of supported compression algorithms.
type     is followed by the list of MIME types that will be compressed.
offload  makes haproxy work as a compression offloader only (see notes).

The currently supported algorithms are :
  identity     this is mostly for debugging, and it was useful for developing
               the compression feature. Identity does not apply any change on
               data.
 
  gzip         applies gzip compression. This setting is only available when
               support for zlib or libslz was built in.
 
  deflate      same as "gzip", but with deflate algorithm and zlib format.
               Note that this algorithm has ambiguous support on many
               browsers and no support at all from recent ones. It is
               strongly recommended not to use it for anything else than
               experimentation. This setting is only available when support
               for zlib or libslz was built in.
 
  raw-deflate  same as "deflate" without the zlib wrapper, and used as an
               alternative when the browser wants "deflate". All major
               browsers understand it and despite violating the standards,
               it is known to work better than "deflate", at least on MSIE
               and some versions of Safari. Do not use it in conjunction
               with "deflate", use either one or the other since both react
               to the same Accept-Encoding token. This setting is only
               available when support for zlib or libslz was built in.
 
Compression will be activated depending on the Accept-Encoding request
header. With identity, it does not take care of that header.
If backend servers support HTTP compression, these directives
will be no-op: haproxy will see the compressed response and will not
compress again. If backend servers do not support HTTP compression and
there is Accept-Encoding header in request, haproxy will compress the
matching response.
 
The "offload" setting makes haproxy remove the Accept-Encoding header to
prevent backend servers from compressing responses. It is strongly
recommended not to do this because this means that all the compression work
will be done on the single point where haproxy is located. However in some
deployment scenarios, haproxy may be installed in front of a buggy gateway
with broken HTTP compression implementation which can't be turned off.
In that case haproxy can be used to prevent that gateway from emitting
invalid payloads. In this case, simply removing the header in the
configuration does not work because it applies before the header is parsed,
so that prevents haproxy from compressing. The "offload" setting should
then be used for such scenarios. Note: for now, the "offload" setting is
ignored when set in a defaults section.
 
Compression is disabled when:
  * the request does not advertise a supported compression algorithm in the
    "Accept-Encoding" header
  * the response message is not HTTP/1.1
  * HTTP status code is not one of 200, 201, 202, or 203
  * response contain neither a "Content-Length" header nor a
    "Transfer-Encoding" whose last value is "chunked"
  * response contains a "Content-Type" header whose first value starts with
    "multipart"
  * the response contains the "no-transform" value in the "Cache-control"
    header
  * User-Agent matches "Mozilla/4" unless it is MSIE 6 with XP SP2, or MSIE 7
    and later
  * The response contains a "Content-Encoding" header, indicating that the
    response is already compressed (see compression offload)
  * The response contains an invalid "ETag" header or multiple ETag headers
 
Note: The compression does not emit the Warning header.

Examples :

compression algo gzip
compression type text/html text/plain

contimeout (deprecated)

Set the maximum time to wait for a connection attempt to a server to succeed.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value is specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

If the server is located on the same LAN as haproxy, the connection should be
immediate (less than a few milliseconds). Anyway, it is a good practice to
cover one or several TCP packet losses by specifying timeouts that are
slightly above multiples of 3 seconds (e.g. 4 or 5 seconds). By default, the
connect timeout also presets the queue timeout to the same value if this one
has not been specified. Historically, the contimeout was also used to set the
tarpit timeout in a listen section, which is not possible in a pure frontend.
 
This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of failed sessions in
the system if the system's timeouts are not configured either.
 
This parameter is provided for backwards compatibility but is currently
deprecated. Please use "", "timeout queue" or ""
instead.

See also : “timeout connect“, ““, “timeout tarpit“, ““, “contimeout“.

[ rewrite | insert | prefix ] [ indirect ] [ nocache ] [ postonly ] [ preserve ] [ httponly ] [ secure ] [ domain ]* [ maxidle ] [ maxlife ] [ dynamic ] [ attr ]*

Enable cookie-based persistence in a backend.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<name>    is the name of the cookie which will be monitored, modified or
          inserted in order to bring persistence. This cookie is sent to
          the client via a "Set-Cookie" header in the response, and is
          brought back by the client in a "Cookie" header in all requests.
          Special care should be taken to choose a name which does not
          conflict with any likely application cookie. Also, if the same
          backends are subject to be used by the same clients (e.g.
          HTTP/HTTPS), care should be taken to use different cookie names
          between all backends if persistence between them is not desired.
 
rewrite   This keyword indicates that the cookie will be provided by the
          server and that haproxy will have to modify its value to set the
          server's identifier in it. This mode is handy when the management
          of complex combinations of "Set-cookie" and "Cache-control"
          headers is left to the application. The application can then
          decide whether or not it is appropriate to emit a persistence
          cookie. Since all responses should be monitored, this mode
          doesn't work in HTTP tunnel mode. Unless the application
          behavior is very complex and/or broken, it is advised not to
          start with this mode for new deployments. This keyword is
          incompatible with "insert" and "prefix".
 
insert    This keyword indicates that the persistence cookie will have to
          be inserted by haproxy in server responses if the client did not
 
          already have a cookie that would have permitted it to access this
          server. When used without the "preserve" option, if the server
          emits a cookie with the same name, it will be removed before
          processing. For this reason, this mode can be used to upgrade
          existing configurations running in the "rewrite" mode. The cookie
          will only be a session cookie and will not be stored on the
          client's disk. By default, unless the "indirect" option is added,
          the server will see the cookies emitted by the client. Due to
          caching effects, it is generally wise to add the "nocache" or
          "postonly" keywords (see below). The "insert" keyword is not
          compatible with "rewrite" and "prefix".
 
prefix    This keyword indicates that instead of relying on a dedicated
          cookie for the persistence, an existing one will be completed.
          This may be needed in some specific environments where the client
          does not support more than one single cookie and the application
          already needs it. In this case, whenever the server sets a cookie
          named <name>, it will be prefixed with the server's identifier
          and a delimiter. The prefix will be removed from all client
          requests so that the server still finds the cookie it emitted.
          Since all requests and responses are subject to being modified,
          this mode doesn't work with tunnel mode. The "prefix" keyword is
          not compatible with "rewrite" and "insert". Note: it is highly
          recommended not to use "indirect" with "prefix", otherwise server
          cookie updates would not be sent to clients.
 
indirect  When this option is specified, no cookie will be emitted to a
          client which already has a valid one for the server which has
          processed the request. If the server sets such a cookie itself,
          it will be removed, unless the "preserve" option is also set. In
          "insert" mode, this will additionally remove cookies from the
          requests transmitted to the server, making the persistence
          mechanism totally transparent from an application point of view.
          Note: it is highly recommended not to use "indirect" with
          "prefix", otherwise server cookie updates would not be sent to
          clients.
 
nocache   This option is recommended in conjunction with the insert mode
          when there is a cache between the client and HAProxy, as it
          ensures that a cacheable response will be tagged non-cacheable if
          a cookie needs to be inserted. This is important because if all
          persistence cookies are added on a cacheable home page for
          instance, then all customers will then fetch the page from an
          outer cache and will all share the same persistence cookie,
          leading to one server receiving much more traffic than others.
          See also the "insert" and "postonly" options.
 
postonly  This option ensures that cookie insertion will only be performed
          on responses to POST requests. It is an alternative to the
          "nocache" option, because POST responses are not cacheable, so
          this ensures that the persistence cookie will never get cached.
          Since most sites do not need any sort of persistence before the
          first POST which generally is a login request, this is a very
          efficient method to optimize caching without risking to find a
          persistence cookie in the cache.
          See also the "insert" and "nocache" options.
 
preserve  This option may only be used with "insert" and/or "indirect". It
          allows the server to emit the persistence cookie itself. In this
          case, if a cookie is found in the response, haproxy will leave it
          untouched. This is useful in order to end persistence after a
          logout request for instance. For this, the server just has to
          emit a cookie with an invalid value (e.g. empty) or with a date in
          the past. By combining this mechanism with the "disable-on-404"
          check option, it is possible to perform a completely graceful
          shutdown because users will definitely leave the server after
          they logout.
 
httponly  This option tells haproxy to add an "HttpOnly" cookie attribute
          when a cookie is inserted. This attribute is used so that a
          user agent doesn't share the cookie with non-HTTP components.
          Please check RFC6265 for more information on this attribute.
 
secure    This option tells haproxy to add a "Secure" cookie attribute when
          a cookie is inserted. This attribute is used so that a user agent
          never emits this cookie over non-secure channels, which means
          that a cookie learned with this flag will be presented only over
          SSL/TLS connections. Please check RFC6265 for more information on
          this attribute.
 
domain    This option allows to specify the domain at which a cookie is
          inserted. It requires exactly one parameter: a valid domain
          name. If the domain begins with a dot, the browser is allowed to
          use it for any host ending with that name. It is also possible to
          specify several domain names by invoking this option multiple
          times. Some browsers might have small limits on the number of
          domains, so be careful when doing that. For the record, sending
          10 domains to MSIE 6 or Firefox 2 works as expected.
 
maxidle   This option allows inserted cookies to be ignored after some idle
          time. It only works with insert-mode cookies. When a cookie is
          sent to the client, the date this cookie was emitted is sent too.
          Upon further presentations of this cookie, if the date is older
          than the delay indicated by the parameter (in seconds), it will
          be ignored. Otherwise, it will be refreshed if needed when the
          response is sent to the client. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). When
          this option is set and a cookie has no date, it is always
          accepted, but gets refreshed in the response. This maintains the
          ability for admins to access their sites. Cookies that have a
          date in the future further than 24 hours are ignored. Doing so
          lets admins fix timezone issues without risking kicking users off
          the site.
 
maxlife   This option allows inserted cookies to be ignored after some life
          time, whether they're in use or not. It only works with insert
          mode cookies. When a cookie is first sent to the client, the date
          this cookie was emitted is sent too. Upon further presentations
          of this cookie, if the date is older than the delay indicated by
          the parameter (in seconds), it will be ignored. If the cookie in
          the request has no date, it is accepted and a date will be set.
          Cookies that have a date in the future further than 24 hours are
          ignored. Doing so lets admins fix timezone issues without risking
          kicking users off the site. Contrary to maxidle, this value is
          not refreshed, only the first visit date counts. Both maxidle and
          maxlife may be used at the time. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). This
          is stronger than the maxidle method in that it forces a
          redispatch after some absolute delay.
 
dynamic   Activate dynamic cookies. When used, a session cookie is
          dynamically created for each server, based on the IP and port
          of the server, and a secret key, specified in the
          "dynamic-cookie-key" backend directive.
          The cookie will be regenerated each time the IP address change,
          and is only generated for IPv4/IPv6.
 
attr      This option tells haproxy to add an extra attribute when a
          cookie is inserted. The attribute value can contain any
          characters except control ones or ";". This option may be
          repeated.

There can be only one persistence cookie per HTTP backend, and it can be
declared in a defaults section. The value of the cookie will be the value
indicated after the "
This keyword is available in sections :
Alphabetically sorted keywords reference
Fetching HTTP samples (Layer 7)
" keyword in a "
This keyword is available in sections :
Peers
" statement. If no cookie
is declared for a given server, the cookie is not set.

Examples :

cookie JSESSIONID prefix
cookie SRV insert indirect nocache
cookie SRV insert postonly indirect
cookie SRV insert indirect nocache maxidle 30m maxlife 8h

See also : “balance source”, “capture cookie“, “

• This keyword is available in sections :
• Peers

“ and “ignore-persist“.

[ request | response ] len

Declares a capture slot.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments:

<length> is the length allowed for the capture.

This declaration is only available in the frontend or listen section, but the
reserved slot can be used in the backends. The "request" keyword allocates a
capture slot for use in the request, and "response" allocates a capture slot
for use in the response.

See also: “capture-req“, ““ (sample converters), “capture.req.hdr“, ““ (sample fetches), “http-request capture“ and ““.

default-server [param*]

Change default options for a server in a backend

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments:

<param*>  is a list of parameters for this server. The "
This keyword is available in sections :
Peers
"
          keyword accepts an important number of options and has a complete
          section dedicated to it. Please refer to section 5 for more
          details.

Example :

default-server inter 1000 weight 13

See also: “

• This keyword is available in sections :
• Peers

“ and section 5 about server options

Specify the backend to use when no "use_backend" rule has been matched.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<backend> is the name of the backend to use.

When doing content-switching between frontend and backends using the
"" keyword, it is often useful to indicate which backend will be
used when no rule has matched. It generally is the dynamic backend which
will catch all undetermined requests.

Example :

use_backend     dynamic  if  url_dyn
use_backend     static   if  url_css url_img extension_img
default_backend dynamic

See also : “use_backend“

Describe a listen, frontend or backend.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments : string

Allows to add a sentence to describe the related object in the HAProxy HTML
stats page. The description will be printed on the right of the object name
it describes.
No need to backslash spaces in the <string> arguments.

disabled

Disable a proxy, frontend or backend.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

The "
This keyword is available in sections :
Peers
Server and default-server options
" keyword is used to disable an instance, mainly in order to
liberate a listening port or to temporarily disable a service. The instance
will still be created and its configuration will be checked, but it will be
created in the "stopped" state and will appear as such in the statistics. It
will not receive any traffic nor will it send any health-checks or logs. It
is possible to disable many instances at once by adding the "
This keyword is available in sections :
Peers
Server and default-server options
"
keyword in a "defaults" section.

See also : “

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“

dispatch

:

Set a default server address

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<address> is the IPv4 address of the default server. Alternatively, a
          resolvable hostname is supported, but this name will be resolved
          during start-up.
 
<ports>   is a mandatory port specification. All connections will be sent
          to this port, and it is not permitted to use port offsets as is
          possible with normal servers.

The "" keyword designates a default server for use when no other
server can take the connection. In the past it was used to forward non
persistent connections to an auxiliary load balancer. Due to its simple
syntax, it has also been used for simple TCP relays. It is recommended not to
use it for more clarity, and to use the "server
This keyword is available in sections :
Alphabetically sorted keywords reference
" directive instead.

See also : “

• This keyword is available in sections :
• Peers

“

dynamic-cookie-key

Set the dynamic cookie secret key for a backend.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : The secret key to be used.

When dynamic cookies are enabled (see the "dynamic" directive for cookie),
a dynamic cookie is created for each server (unless one is explicitly
specified on the "
This keyword is available in sections :
Peers
" line), using a hash of the IP address of the
server, the TCP port, and the secret key.
That way, we can ensure session persistence across multiple load-balancers,
even if servers are dynamically added or removed.

enabled

Enable a proxy, frontend or backend.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

The "
This keyword is available in sections :
Alphabetically sorted keywords reference
" keyword is used to explicitly enable an instance, when the
defaults has been set to "disabled
This keyword is available in sections :
Alphabetically sorted keywords reference
". This is very rarely used.

See also : “disabled

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“

errorfile

Return a file contents instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.
 
<file>    designates a file containing the full HTTP response. It is
          recommended to follow the common practice of appending ".http" to
          the filename so that people do not confuse the response with HTML
          error pages, and to use absolute paths, since files are read
          before any chroot is performed.

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
 
Code 200 is emitted in response to requests matching a "" rule.
 
The files are returned verbatim on the TCP socket. This allows any trick such
as redirections to another URL or site, as well as tricks to clean cookies,
force enable or disable caching, etc... The package provides default error
files returning the same contents as default errors.
 
The files should not exceed the configured buffer size (BUFSIZE), which
generally is 8 or 16 kB, otherwise they will be truncated. It is also wise
not to put any reference to local contents (e.g. images) in order to avoid
loops between the client and HAProxy when all servers are down, causing an
error to be returned instead of an image. For better HTTP compliance, it is
recommended that all header lines end with CR-LF and not LF alone.
 
The files are read at the same time as the configuration and kept in memory.
For this reason, the errors continue to be returned even when the process is
simple method for developing those files consists in associating them to the
403 status code and interrogating a blocked URL.

See also : “errorloc“, ““, “errorloc303“

Example :

errorfile 400 /etc/haproxy/errorfiles/400badreq.http
errorfile 408 /dev/null  # work around Chrome pre-connect bug
errorfile 403 /etc/haproxy/errorfiles/403forbid.http
errorfile 503 /etc/haproxy/errorfiles/503sorry.http

errorloc302

Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.
 
<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
 
Code 200 is emitted in response to requests matching a "" rule.
 
Note that both keyword return the HTTP 302 status code, which tells the
client to fetch the designated URL using the same HTTP method. This can be
quite problematic in case of non-GET methods such as POST, because the URL
sent to the client might not be allowed for something other than GET. To
work around this problem, please use "errorloc303" which send the HTTP 303
status code, indicating to the client that the URL must be fetched with a GET
request.

See also : ““, “errorloc303“

Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.
 
<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
 
Code 200 is emitted in response to requests matching a "monitor-uri" rule.
 
Note that both keyword return the HTTP 303 status code, which tells the
client to fetch the designated URL using the same HTTP GET method. This
solves the usual problems associated with "" and the 302 code. It is
possible that some very old browsers designed before HTTP/1.1 do not support
it, but no such problem has been reported till now.

See also : “errorfile“, ““, “errorloc302“

Declare the from email address to be used in both the envelope and header
of email alerts. This is the address that email alerts are sent from.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<emailaddr> is the from email address to use when sending email alerts

Also requires "email-alert mailers" and "" to be set
and if so sending email alerts is enabled for the proxy.

See also : “email-alert level“, ““, “email-alert myhostname“, ““, section 3.6 about mailers.

Declare the maximum log level of messages for which email alerts will be
sent. This acts as a filter on the sending of email alerts.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<level> One of the 8 syslog levels:
          emerg alert crit err warning notice info  debug
        The above syslog levels are ordered from lowest to highest.

By default level is alert
 
Also requires "email-alert from", "" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.
 
Alerts are sent when :
 
* An un-paused server is marked as down and <level> is alert or lower
* A paused server is marked as down and <level> is notice or lower
* A server is marked as up or enters the drain state and <level>
  is notice or lower
* "" is enabled, <level> is info or lower,
   and a health check status update occurs

See also : “email-alert from“, ““, “email-alert myhostname“, ““, section 3.6 about mailers.

Declare the mailers to be used when sending email alerts

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<mailersect> is the name of the mailers section to send email alerts.

Also requires "email-alert from" and "" to be set
and if so sending email alerts is enabled for the proxy.

See also : “email-alert from“, ““, “email-alert myhostname“, ““, section 3.6 about mailers.

Declare the to hostname address to be used when communicating with
mailers.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<hostname> is the hostname to use when communicating with mailers

By default the systems hostname is used.
 
Also requires "email-alert from", "" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.

See also : ““, “email-alert level“, ““, “email-alert to“, about mailers.

email-alert to

Declare both the recipient address in the envelope and to address in the
header of email alerts. This is the address that email alerts are sent to.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<emailaddr> is the to email address to use when sending email alerts

Also requires "" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.

See also : ““, “email-alert level“, ““, “email-alert myhostname“, about mailers.

force-persist { if | unless }

Declare a condition to force persistence on down servers

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

By default, requests are not dispatched to down servers. It is possible to
force this using "", but it is unconditional and redispatches
to a valid server if "option redispatch" is set. That leaves with very little
possibilities to force some requests to reach a server which is artificially
marked down for maintenance operations.
 
The "" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore the down status of
a server and still try to connect to it. That makes it possible to start a
server, still replying an error to the health checks, and run a specially
configured browser to test the service. Among the handy methods, one could
use a specific source IP address, or a specific cookie. The cookie also has
the advantage that it can easily be added/removed on the browser from a test
page. Once the service is validated, it is then possible to open the service
to the world by returning a valid response to health checks.
 
The forced persistence is enabled when an "if" condition is met, or unless an
"unless" condition is met. The final redispatch is always disabled when this
is used.

See also : “option redispatch“, ““, “persist“, and about ACL usage.

filter [param*]

Add the filter <name> in the filter list attached to the proxy.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<name>     is the name of the filter. Officially supported filters are
           referenced in .
 
<param*>   is a list of parameters accepted by the filter <name>. The
           parsing of these parameters are the responsibility of the
           filter. Please refer to the documentation of the corresponding
           filter (section 9) for all details on the supported parameters.

Multiple occurrences of the filter line can be used for the same proxy. The
same filter can be referenced many times if needed.

Example:

listen
  bind *:80
  filter trace name BEFORE-HTTP-COMP
  filter compression
  filter trace name AFTER-HTTP-COMP
  compression algo gzip
  compression offload
  server srv1 192.168.0.1:80

See also : .

fullconn

Specify at what backend load the servers will reach their maxconn

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<conns>   is the number of connections on the backend which will make the
          servers use the maximal number of connections.

When a server has a "
This keyword is available in sections :
Performance tuning
Bind options
" parameter specified, it means that its number
of concurrent connections will never go higher. Additionally, if it has a
"minconn" parameter, it indicates a dynamic limit following the backend's
load. The server will then always accept at least <minconn> connections,
never more than <maxconn>, and the limit will be on the ramp between both
values when the backend has less than <conns> concurrent connections. This
makes it possible to limit the load on the servers during normal loads, but
push it further for important loads without overloading the servers during
exceptional loads.
 
Since it's hard to get this value right, haproxy automatically sets it to
10% of the sum of the maxconns of all frontends that may branch to this
backend (based on "" and "default_backend" rules). That way it's
safe to leave it unset. However, "" involving dynamic names are
not counted since there is no way to know if they could match or not.

Example :

# The servers will accept between 100 and 1000 concurrent connections each
# and the maximum of 1000 will be reached when the backend reaches 10000
# connections.
backend dynamic
   fullconn   10000
   server     srv1   dyn1:80 minconn 100 maxconn 1000
   server     srv2   dyn2:80 minconn 100 maxconn 1000

See also : “maxconn

• This keyword is available in sections :
• Alphabetically sorted keywords reference
• Server and default-server options

“, “

• This keyword is available in sections :
• Peers

“

grace

Maintain a proxy operational for some time after a soft stop

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<time>    is the time (by default in milliseconds) for which the instance
          will remain operational with the frontend sockets still listening
          when a soft-stop is received via the SIGUSR1 signal.

This may be used to ensure that the services disappear in a certain order.
This was designed so that frontends which are dedicated to monitoring by an
external equipment fail immediately while other ones remain up for the time
needed by the equipment to detect the failure.
 
Note that currently, there is very little benefit in using this parameter,
and it may in fact complicate the soft-reconfiguration process more than
simplify it.

Specify the balancing factor for bounded-load consistent hashing

May be used in sections :

defaults	frontend	listen	backend
yes	no	no	yes

Arguments :

<factor> is the control for the maximum number of concurrent requests to
         send to a server, expressed as a percentage of the average number
         of concurrent requests across all of the active servers.

Specifying a "hash-balance-factor" for a server with "hash-type consistent"
enables an algorithm that prevents any one server from getting too many
requests at once, even if some hash buckets receive many more requests than
others. Setting <factor> to 0 (the default) disables the feature. Otherwise,
<factor> is a percentage greater than 100. For example, if <factor> is 150,
then no server will be allowed to have a load more than 1.5 times the average.
If server weights are used, they will be respected.
 
If the first-choice server is disqualified, the algorithm will choose another
server based on the request hash, until a server with additional capacity is
found. A higher <factor> allows more imbalance between the servers, while a
lower <factor> means that more servers will be checked on average, affecting
performance. Reasonable values are from 125 to 200.
 
This setting is also used by "balance random" which internally relies on the
consistent hashing mechanism.

See also : ““ and “hash-type“.

Specify a method to use for mapping hashes to servers

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<method> is the method used to select a server from the hash computed by
         the <function> :
 
  map-based   the hash table is a static array containing all alive servers.
              The hashes will be very smooth, will consider weights, but
              will be static in that weight changes while a server is up
              will be ignored. This means that there will be no slow start.
              Also, since a server is selected by its position in the array,
              most mappings are changed when the server count changes. This
              means that when a server goes up or down, or when a server is
              added to a farm, most connections will be redistributed to
              different servers. This can be inconvenient with caches for
              instance.
 
  consistent  the hash table is a tree filled with many occurrences of each
              server. The hash key is looked up in the tree and the closest
              server is chosen. This hash is dynamic, it supports changing
              weights while the servers are up, so it is compatible with the
              slow start feature. It has the advantage that when a server
              goes up or down, only its associations are moved. When a
              server is added to the farm, only a few part of the mappings
              are redistributed, making it an ideal method for caches.
              However, due to its principle, the distribution will never be
              very smooth and it may sometimes be necessary to adjust a
              server's weight or its ID to get a more balanced distribution.
              In order to get the same distribution on multiple load
              balancers, it is important that all servers have the exact
              same IDs. Note: consistent hash uses sdbm and avalanche if no
              hash function is specified.
 
<function> is the hash function to be used :
 
   sdbm   this function was created initially for sdbm (a public-domain
          reimplementation of ndbm) database library. It was found to do
          well in scrambling bits, causing better distribution of the keys
          and fewer splits. It also happens to be a good general hashing
          function with good distribution, unless the total server weight
          is a multiple of 64, in which case applying the avalanche
          modifier may help.
 
   djb2   this function was first proposed by Dan Bernstein many years ago
          on comp.lang.c. Studies have shown that for certain workload this
          function provides a better distribution than sdbm. It generally
          works well with text-based inputs though it can perform extremely
          poorly with numeric-only input or when the total server weight is
          a multiple of 33, unless the avalanche modifier is also used.
 
   wt6    this function was designed for haproxy while testing other
          functions in the past. It is not as smooth as the other ones, but
          is much less sensible to the input data set or to the number of
          servers. It can make sense as an alternative to sdbm+avalanche or
          djb2+avalanche for consistent hashing or when hashing on numeric
          data such as a source IP address or a visitor identifier in a URL
          parameter.
 
   crc32  this is the most common CRC32 implementation as used in Ethernet,
          gzip, PNG, etc. It is slower than the other ones but may provide
          a better distribution or less predictable results especially when
          used on strings.
 
<modifier> indicates an optional method applied after hashing the key :
 
   avalanche   This directive indicates that the result from the hash
               function above should not be used in its raw form but that
               a 4-byte full avalanche hash must be applied first. The
               purpose of this step is to mix the resulting bits from the
               previous hash in order to avoid any undesired effect when
               the input contains some limited values or when the number of
               servers is a multiple of one of the hash's components (64
               for SDBM, 33 for DJB2). Enabling avalanche tends to make the
               result less predictable, but it's also not as smooth as when
               using the original function. Some testing might be needed
               with some workloads. This hash is one of the many proposed
               by Bob Jenkins.

The default hash type is "map-based" and is recommended for most usages. The
default function is "sdbm", the selection of a function should be based on
the range of the values being hashed.

See also : ““, “hash-balance-factor“, “

• This keyword is available in sections :
• Peers

“

http-check disable-on-404

Enable a maintenance mode upon HTTP/404 response to health-checks

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When this option is set, a server which returns an HTTP code 404 will be
excluded from further load-balancing, but will still receive persistent
connections. This provides a very convenient method for Web administrators
to perform a graceful shutdown of their servers. It is also important to note
that a server which is detected as failed while it was in this mode will not
generate an alert, just a notice. If the server responds 2xx or 3xx again, it
will immediately be reinserted into the farm. The status on the stats page
reports "NOLB" for a server in this mode. It is important to note that this
option only works in conjunction with the "" option. If this option
is used with "http-check expect", then it has precedence over it so that 404
responses will still be considered as soft-stop.

See also : ““, “http-check expect“

[!]

Make HTTP health checks consider response contents or specific status codes

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<match>   is a keyword indicating how to look for a specific pattern in the
          response. The keyword may be one of "status", "rstatus",
          "string", or "rstring". The keyword may be preceded by an
          exclamation mark ("!") to negate the match. Spaces are allowed
          between the exclamation mark and the keyword. See below for more
          details on the supported keywords.
 
<pattern> is the pattern to look for. It may be a string or a regular
          expression. If the pattern contains spaces, they must be escaped
          with the usual backslash ('\').

By default, "" considers that response statuses 2xx and 3xx
are valid, and that others are invalid. When "http-check expect" is used,
it defines what is considered valid or invalid. Only one ""
statement is supported in a backend. If a server fails to respond or times
out, the check obviously fails. The available matches are :
 
  status <string> : test the exact string match for the HTTP status code.
                    A health check response will be considered valid if the
                    response's status code is exactly this string. If the
                    "status" keyword is prefixed with "!", then the response
                    will be considered invalid if the status code matches.
 
  rstatus <regex> : test a regular expression for the HTTP status code.
                    A health check response will be considered valid if the
                    response's status code matches the expression. If the
                    "rstatus" keyword is prefixed with "!", then the response
                    will be considered invalid if the status code matches.
                    This is mostly used to check for multiple codes.
 
  string <string> : test the exact string match in the HTTP response body.
                    A health check response will be considered valid if the
                    response's body contains this exact string. If the
                    "string" keyword is prefixed with "!", then the response
                    will be considered invalid if the body contains this
                    string. This can be used to look for a mandatory word at
                    the end of a dynamic page, or to detect a failure when a
                    specific error appears on the check page (e.g. a stack
                    trace).
 
  rstring <regex> : test a regular expression on the HTTP response body.
                    A health check response will be considered valid if the
                    response's body matches this expression. If the "rstring"
                    keyword is prefixed with "!", then the response will be
                    considered invalid if the body matches the expression.
                    This can be used to look for a mandatory word at the end
                    of a dynamic page, or to detect a failure when a specific
                    error appears on the check page (e.g. a stack trace).
 
It is important to note that the responses will be limited to a certain size
defined by the global "" option, which defaults to 16384 bytes.
Thus, too large responses may not contain the mandatory pattern when using
"string" or "rstring". If a large response is absolutely required, it is
possible to change the default max size by setting the global variable.
However, it is worth keeping in mind that parsing very large responses can
waste some CPU cycles, especially when regular expressions are used, and that
it is always better to focus the checks on smaller resources.
 
Also "http-check expect" doesn't support HTTP keep-alive. Keep in mind that it
will automatically append a "Connection: close" header, meaning that this
header should not be present in the request provided by "".
 
Last, if "http-check expect" is combined with "",
then this last one has precedence when the server responds with 404.

Examples :

# only accept status 200 as valid
http-check expect status 200
# consider SQL errors as errors
http-check expect ! string SQL\ Error
# consider status 5xx only as errors
http-check expect ! rstatus ^5
# check that we have a correct hexadecimal tag before /html
http-check expect rstring <!--tag:[0-9a-f]*--></html>

See also : “option httpchk“, ““

http-check send-state

Enable emission of a state header with HTTP health checks

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When this option is set, haproxy will systematically send a special header
"X-Haproxy-Server-State" with a list of parameters indicating to each server
how they are seen by haproxy. This can be used for instance when a server is
manipulated without access to haproxy and the operator needs to know whether
haproxy still sees it up or not, or if the server is the last one in a farm.
 
The header is composed of fields delimited by semi-colons, the first of which
is a word ("UP", "DOWN", "NOLB"), possibly followed by a number of valid
checks on the total number before transition, just as appears in the stats
interface. Next headers are in the form "<variable>=<value>", indicating in
no specific order some values available in the stats interface :
  - a variable "address", containing the address of the backend server.
    This corresponds to the <address> field in the server declaration. For
    unix domain sockets, it will read "unix".
 
  - a variable "", containing the port of the backend server. This
    corresponds to the <port> field in the server declaration. For unix
    domain sockets, it will read "unix".
 
  - a variable "name", containing the name of the backend followed by a slash
    ("/") then the name of the server. This can be used when a server is
    checked in multiple backends.
 
  - a variable "" containing the name of the haproxy node, as set in the
    global "node" variable, otherwise the system's hostname if unspecified.
 
  - a variable "" indicating the weight of the server, a slash ("/")
    and the total weight of the farm (just counting usable servers). This
    helps to know if other servers are available to handle the load when this
    one fails.
 
  - a variable "scur" indicating the current number of concurrent connections
    on the server, followed by a slash ("/") then the total number of
    connections on all servers of the same backend.
 
  - a variable "qcur" indicating the current number of requests in the
    server's queue.
 
Example of a header received by the application server :
  >>>  X-Haproxy-Server-State: UP 2/3; name=bck/srv2; node=lb1; weight=1/2; \
         scur=13/22; qcur=0

See also : “option httpchk“, ““

http-request [options…] [ { if | unless } ]

Access control for Layer 7 requests

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

The http-request statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Any rule may optionally be
followed by an ACL-based condition, in which case it will only be evaluated
if the condition is true.
 
The first keyword is the rule's action. The supported actions are described
below.
 
There is no limit to the number of http-request statements per instance.
 
It is important to know that http-request rules are processed very early in
the HTTP processing, just after "" rules and before "reqdel" or ""
or "reqadd" rules. That way, headers added by "add-header"/"set-header" are
visible by almost all further ACL rules.
 
Using ""/"reqdel"/"" to manipulate request headers is discouraged
in newer versions (>= 1.5). But if you need to use regular expression to
delete headers, you can still use "reqdel". Also please use
"http-request deny/allow/tarpit" instead of ""/"reqpass"/"".

Example:

acl nagios src 192.168.129.3
acl local_net src 192.168.0.0/16
acl auth_ok http_auth(L1)
http-request allow if nagios
http-request allow if local_net auth_ok
http-request auth realm Gimme if local_net auth_ok
http-request deny

Example:

acl key req.hdr(X-Add-Acl-Key) -m found
acl add path /addacl
acl del path /delacl
acl myhost hdr(Host) -f myhost.lst
http-request add-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key add
http-request del-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key del

Example:

acl value  req.hdr(X-Value) -m found
acl setmap path /setmap
acl delmap path /delmap
use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }
http-request set-map(map.lst) %[src] %[req.hdr(X-Value)] if setmap value
http-request del-map(map.lst) %[src]                     if delmap

See also : “stats http-request“, about userlists and section 7 about ACL usage.

() [ { if | unless } ]

This is used to add a new entry into an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the new entry. It performs a lookup
in the ACL before insertion, to avoid duplicated (or more) values. This
lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "add acl" command from the stats socket, but can
be triggered by an HTTP request.

http-request add-header [ { if | unless } ]

This appends an HTTP header field whose name is specified in <name> and
whose value is defined by <fmt> which follows the log-format rules (see
Custom Log Format in ). This is particularly useful to pass
connection-specific information to the server (e.g. the client's SSL
certificate), or to combine several headers into one. This rule is not
final, so it is possible to add other similar rules. Note that header
addition is performed immediately, so one rule might reuse the resulting
header from a previous rule.

http-request allow [ { if | unless } ]

This stops the evaluation of the rules and lets the request pass the check.
No further "
This keyword is available in sections :
Proxy section
" rules are evaluated.

http-request auth [realm ] [ { if | unless } ]

This stops the evaluation of the rules and immediately responds with an
HTTP 401 or 407 error code to invite the user to present a valid user name
and password. No further "
This keyword is available in sections :
Proxy section
" rules are evaluated. An optional
"realm" parameter is supported, it sets the authentication realm that is
returned with the response (typically the application's name).

Example:

acl auth_ok http_auth_group(L1) G1
http-request auth unless auth_ok

http-request cache-use [ { if | unless } ]

See  about cache setup.

http-request capture [ len | id ] [ { if | unless } ]

This captures sample expression <sample> from the request buffer, and
converts it to a string of at most <len> characters. The resulting string is
stored into the next request "" slot, so it will possibly appear next
to some captured HTTP headers. It will then automatically appear in the logs,
and it will be possible to extract it using sample fetch rules to feed it
into headers or anything. The length should be limited given that this size
will be allocated for each capture during the whole session life.
Please check section 7.3 (Fetching samples) and "" for
more information.
 
If the keyword "id
This keyword is available in sections :
Bind options
" is used instead of "len", the action tries to store the
captured string in a previously declared capture slot. This is useful to run
captures in backends. The slot id can be declared by a previous directive
"http-request capture" or with the "" keyword.
 
When using this action in a backend, double check that the relevant
frontend(s) have the required capture slots otherwise, this rule will be
ignored at run time. This can't be detected at configuration parsing time
due to HAProxy's ability to dynamically resolve backend name at runtime.

http-request del-acl() [ { if | unless } ]

This is used to delete an entry from an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It is the equivalent of the "del acl" command from the stats socket, but can
be triggered by an HTTP request.

[ { if | unless } ]

This removes all HTTP header fields whose name is specified in <name>.

http-request del-map() [ { if | unless } ]

This is used to delete an entry from a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It takes one argument: "file name" It is the equivalent of the "del map"
command from the stats socket, but can be triggered by an HTTP request.

[deny_status ] [ { if | unless } ]

This stops the evaluation of the rules and immediately rejects the request
and emits an HTTP 403 error, or optionally the status code specified as an
argument to "deny_status". The list of permitted status codes is limited to
those that can be overridden by the "errorfile" directive.
No further "
This keyword is available in sections :
Proxy section
" rules are evaluated.

http-request disable-l7-retry [ { if | unless } ]

This disables any attempt to retry the request if it fails for any other
reason than a connection failure. This can be useful for example to make
sure POST requests aren't retried on failure.

(,,[ipv4,ipv6]) :

This action performs a DNS resolution of the output of <expr> and stores
the result in the variable <var>. It uses the DNS resolvers section
pointed by <resolvers>.
It is possible to choose a resolution preference using the optional
arguments 'ipv4' or 'ipv6'.
When performing the DNS resolution, the client side connection is on
pause waiting till the end of the resolution.
If an IP address can be found, it is stored into <var>. If any kind of
error occurs, then <var> is not set.
One can use this action to discover a server IP address at run time and
based on information found in the request (IE a Host header).
If this action is used to find the server's IP address (using the
"set-dst" action), then the server IP address in the backend must be set
to 0.0.0.0.

Example:

  nameserver local 127.0.0.53:53
  nameserver google 8.8.8.8:53
  timeout retry   1s
  hold valid 10s
  hold nx 3s
  hold other 3s
  hold obsolete 0s
  accepted_payload_size 8192
frontend fe
  bind 10.42.0.1:80
  http-request do-resolve(txn.myip,mydns,ipv4) hdr(Host),lower
  http-request capture var(txn.myip) len 40
  # return 503 when the variable is not set,
  # which mean DNS resolution error
  use_backend b_503 unless { var(txn.myip) -m found }
  default_backend be
backend b_503
  # dummy backend used to return 503.
  # one can use the errorfile directive to send a nice
  # 503 error page to end users
backend be
  # rule to prevent HAProxy from reconnecting to services
  # on the local network (forged DNS name used to scan the network)
  http-request deny if { var(txn.myip) -m ip 127.0.0.0/8 10.0.0.0/8 }
  http-request set-dst var(txn.myip)
  server clear 0.0.0.0:0

NOTE: Don't forget to set the "protection" rules to ensure HAProxy won't
      be used to scan the network or worst won't loop over itself...

http-request early-hint [ { if | unless } ]

This is used to build an HTTP 103 Early Hints response prior to any other one.
This appends an HTTP header field to this response whose name is specified in
<name> and whose value is defined by <fmt> which follows the log-format rules
(see Custom Log Format in ). This is particularly useful to pass
to the client some Link headers to preload resources required to render the
HTML documents.
 
See RFC 8297 for more information.

http-request redirect [ { if | unless } ]

This performs an HTTP redirection based on a redirect rule. This is exactly
the same as the "" statement except that it inserts a redirect rule
which can be processed in the middle of other "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
" rules and that
these rules use the "" strings. See the "redirect" keyword for the
rule's syntax.

[ { if | unless } ]

This stops the evaluation of the rules and immediately closes the connection
without sending any response. It acts similarly to the
"tcp-request content reject" rules. It can be useful to force an immediate
connection closure on HTTP/2 connections.

http-request replace-header [ { if | unless } ]

This matches the value of all occurrences of header field <name> against
<match-regex>. Matching is performed case-sensitively. Matching values are
completely replaced by <replace-fmt>. Format characters are allowed in
<replace-fmt> and work like <fmt> arguments in "".
Standard back-references using the backslash ('\') followed by a number are
supported.
 
This action acts on whole header lines, regardless of the number of values
they may contain. Thus it is well-suited to process headers naturally
containing commas in their value, such as If-Modified-Since. Headers that
contain a comma-separated list of values, such as Accept, should be processed
using "http-request replace-value".

Example:

http-request replace-header Cookie foo=([^;]*);(.*) foo=\1;ip=%bi;\2
# applied to:
Cookie: foo=foobar; expires=Tue, 14-Jun-2016 01:40:45 GMT;
# outputs:
Cookie: foo=foobar;ip=192.168.1.20; expires=Tue, 14-Jun-2016 01:40:45 GMT;
# assuming the backend IP is 192.168.1.20
http-request replace-header User-Agent curl foo
# applied to:
User-Agent: curl/7.47.0
# outputs:
User-Agent: foo

[ { if | unless } ]

This works like "replace-header" except that it works on the request's path
component instead of a header. The path component starts at the first '/'
after an optional scheme+authority. It does contain the query string if any
is present. The replacement does not modify the scheme nor authority.
 
It is worth noting that regular expressions may be more expensive to evaluate
than certain ACLs, so rare replacements may benefit from a condition to avoid
performing the evaluation at all if it does not match.

Example:

# prefix /foo : turn /bar?q=1 into /foo/bar?q=1 :
http-request replace-path (.*) /foo\1
# suffix /foo : turn /bar?q=1 into /bar/foo?q=1 :
http-request replace-path ([^?]*)(\?(.*))? \1/foo\2
# strip /foo : turn /foo/bar?q=1 into /bar?q=1
http-request replace-path /foo/(.*) /\1
# or more efficient if only some requests match :
http-request replace-path /foo/(.*) /\1 if { url_beg /foo/ }

http-request replace-uri [ { if | unless } ]

This works like "replace-header" except that it works on the request's URI part
instead of a header. The URI part may contain an optional scheme, authority or
query string. These are considered to be part of the value that is matched
against.
 
It is worth noting that regular expressions may be more expensive to evaluate
than certain ACLs, so rare replacements may benefit from a condition to avoid
performing the evaluation at all if it does not match.
 
IMPORTANT NOTE: historically in HTTP/1.x, the vast majority of requests sent
by browsers use the "origin form", which differs from the "absolute form" in
that they do not contain a scheme nor authority in the URI portion. Mostly
only requests sent to proxies, those forged by hand and some emitted by
certain applications use the absolute form. As such, "replace-uri" usually
works fine most of the time in HTTP/1.x with rules starting with a "/". But
with HTTP/2, clients are encouraged to send absolute URIs only, which look
like the ones HTTP/1 clients use to talk to proxies. Such partial replace-uri
rules may then fail in HTTP/2 when they work in HTTP/1. Either the rules need
to be adapted to optionally match a scheme and authority, or replace-path
should be used.

Example:

# rewrite all "http" absolute requests to "https":
http-request replace-uri ^http://(.*) https://\1
# prefix /foo : turn /bar?q=1 into /foo/bar?q=1 :
http-request replace-uri ([^/:]*://[^/]*)?(.*) \1/foo\2

[ { if | unless } ]

This works like "replace-header" except that it matches the regex against
every comma-delimited value of the header field <name> instead of the
entire header. This is suited for all headers which are allowed to carry
more than one value. An example could be the Accept header.

Example:

http-request replace-value X-Forwarded-For ^192\.168\.(.*)$ 172.16.\1
# applied to:
X-Forwarded-For: 192.168.10.1, 192.168.13.24, 10.0.0.37
# outputs:
X-Forwarded-For: 172.16.10.1, 172.16.13.24, 10.0.0.37

http-request sc-inc-gpc0() [ { if | unless } ]

() [ { if | unless } ]

This actions increments the GPC0 or GPC1 counter according with the sticky
counter designated by <sc-id>. If an error occurs, this action silently fails
and the actions evaluation continues.

http-request sc-set-gpt0() [ { if | unless } ]

This action sets the GPT0 tag according to the sticky counter designated by
<sc-id> and the value of <int>. The expected result is a boolean. If an error
occurs, this action silently fails and the actions evaluation continues.

[ { if | unless } ]

This is used to set the destination IP address to the value of specified
expression. Useful when a proxy in front of HAProxy rewrites destination IP,
but provides the correct IP in a HTTP header; or you want to mask the IP for
privacy. If you want to connect to the new address/port, use '0.0.0.0:0' as a
server address in the backend.

Arguments:

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

Example:

http-request set-dst hdr(x-dst)
http-request set-dst dst,ipmask(24)

When possible, set-dst preserves the original destination port as long as the
address family allows it, otherwise the destination port is set to 0.

http-request set-dst-port [ { if | unless } ]

This is used to set the destination port address to the value of specified
expression. If you want to connect to the new address/port, use '0.0.0.0:0'
as a server address in the backend.

Arguments:

<expr>  Is a standard HAProxy expression formed by a sample-fetch
        followed by some converters.

Example:

http-request set-dst-port hdr(x-port)
http-request set-dst-port int(4000)

When possible, set-dst-port preserves the original destination address as
long as the address family supports a port, otherwise it forces the
destination address to IPv4 "0.0.0.0" before rewriting the port.

[ { if | unless } ]

This does the same as "http-request add-header" except that the header name
is first removed if it existed. This is useful when passing security
information to the server, where the header must not be manipulated by
external users. Note that the new value is computed before the removal so it
is possible to concatenate a value to an existing header.

Example:

http-request set-header X-Haproxy-Current-Date %T
http-request set-header X-SSL                  %[ssl_fc]
http-request set-header X-SSL-Session_ID       %[ssl_fc_session_id,hex]
http-request set-header X-SSL-Client-Verify    %[ssl_c_verify]
http-request set-header X-SSL-Client-DN        %{+Q}[ssl_c_s_dn]
http-request set-header X-SSL-Client-CN        %{+Q}[ssl_c_s_dn(cn)]
http-request set-header X-SSL-Issuer           %{+Q}[ssl_c_i_dn]
http-request set-header X-SSL-Client-NotBefore %{+Q}[ssl_c_notbefore]
http-request set-header X-SSL-Client-NotAfter  %{+Q}[ssl_c_notafter]

[ { if | unless } ]

This is used to change the log level of the current request when a certain
condition is met. Valid levels are the 8 syslog levels (see the "log
This keyword is available in sections :
Alphabetically sorted keywords reference
"
keyword) plus the special level "silent" which disables logging for this
request. This rule is not final so the last matching rule wins. This rule
can be useful to disable health checks coming from another equipment.

() [ { if | unless } ]

This is used to add a new entry into a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes 2 arguments: <key fmt>, which follows
log-format rules, used to collect MAP key, and <value fmt>, which follows
log-format rules, used to collect content for the new entry.
It performs a lookup in the MAP before insertion, to avoid duplicated (or
more) values. This lookup is done by a linear search and can be expensive
with large lists! It is the equivalent of the "set map" command from the
stats socket, but can be triggered by an HTTP request.

http-request set-mark [ { if | unless } ]

This is used to set the Netfilter MARK on all packets sent to the client to
the value passed in <mark> on platforms which support it. This value is an
unsigned 32 bit value which can be matched by netfilter and by the routing
table. It can be expressed both in decimal or hexadecimal format (prefixed by
"0x"). This can be useful to force certain packets to take a different route
(for example a cheaper network path for bulk downloads). This works on Linux
kernels 2.6.32 and above and requires admin privileges.

[ { if | unless } ]

This rewrites the request method with the result of the evaluation of format
string <fmt>. There should be very few valid reasons for having to do so as
this is more likely to break something than to fix it.

http-request set-nice [ { if | unless } ]

This sets the "" factor of the current request being processed. It only
has effect against the other requests being processed at the same time.
The default value is 0, unless altered by the "nice" setting on the "
This keyword is available in sections :
Peers
"
line. The accepted range is -1024..1024. The higher the value, the nicest
the request will be. Lower values will make the request more important than
other ones. This can be useful to improve the speed of some requests, or
lower the priority of non-important requests. Using this setting without
prior experimentation can cause some major slowdown.

http-request set-path [ { if | unless } ]

This rewrites the request path with the result of the evaluation of format
string <fmt>. The query string, if any, is left intact. If a scheme and
authority is found before the path, they are left intact as well. If the
request doesn't have a path ("*"), this one is replaced with the format.
This can be used to prepend a directory component in front of a path for
example. See also "" and "http-request set-uri".

Example :

# prepend the host name before the path
http-request set-path /%[hdr(host)]%[path]

[ { if | unless } ]

This is used to set the queue priority class of the current request.
The value must be a sample expression which converts to an integer in the
range -2047..2047. Results outside this range will be truncated.
The priority class determines the order in which queued requests are
processed. Lower values have higher priority.

http-request set-priority-offset [ { if | unless } ]

This is used to set the queue priority timestamp offset of the current
request. The value must be a sample expression which converts to an integer
in the range -524287..524287. Results outside this range will be truncated.
When a request is queued, it is ordered first by the priority class, then by
the current timestamp adjusted by the given offset in milliseconds. Lower
values have higher priority.
Note that the resulting timestamp is is only tracked with enough precision
for 524,287ms (8m44s287ms). If the request is queued long enough to where the
adjusted timestamp exceeds this value, it will be misidentified as highest
priority. Thus it is important to set "" to a value, where when
combined with the offset, does not exceed this limit.

http-request set-query [ { if | unless } ]

This rewrites the request's query string which appears after the first
question mark ("?") with the result of the evaluation of format string <fmt>.
The part prior to the question mark is left intact. If the request doesn't
contain a question mark and the new value is not empty, then one is added at
the end of the URI, followed by the new value. If a question mark was
present, it will never be removed even if the value is empty. This can be
used to add or remove parameters from the query string.
 
See also "" and "http-request set-uri".

Example:

# replace "%3D" with "=" in the query string
http-request set-query %[query,regsub(%3D,=,g)]

[ { if | unless } ]

This is used to set the source IP address to the value of specified
expression. Useful when a proxy in front of HAProxy rewrites source IP, but
provides the correct IP in a HTTP header; or you want to mask source IP for
privacy.

Arguments :

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

Example:

http-request set-src hdr(x-forwarded-for)
http-request set-src src,ipmask(24)

When possible, set-src preserves the original source port as long as the
address family allows it, otherwise the source port is set to 0.

http-request set-src-port [ { if | unless } ]

This is used to set the source port address to the value of specified
expression.

Arguments:

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

Example:

http-request set-src-port hdr(x-port)
http-request set-src-port int(4000)

When possible, set-src-port preserves the original source address as long as
the address family supports a port, otherwise it forces the source address to
IPv4 "0.0.0.0" before rewriting the port.

[ { if | unless } ]

This is used to set the TOS or DSCP field value of packets sent to the client
to the value passed in <tos> on platforms which support this. This value
represents the whole 8 bits of the IP TOS field, and can be expressed both in
decimal or hexadecimal format (prefixed by "0x"). Note that only the 6 higher
bits are used in DSCP or TOS, and the two lower bits are always 0. This can
be used to adjust some routing behavior on border routers based on some
information from the request.
 
See RFC 2474, 2597, 3260 and 4594 for more information.

http-request set-uri [ { if | unless } ]

This rewrites the request URI with the result of the evaluation of format
string <fmt>. The scheme, authority, path and query string are all replaced
at once. This can be used to rewrite hosts in front of proxies, or to
perform complex modifications to the URI such as moving parts between the
path and the query string.
See also "" and "http-request set-query".

() [ { if | unless } ]

This is used to set the contents of a variable. The variable is declared
inline.

Arguments:

<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed are:
              "proc" : the variable is shared with the whole process
              "sess" : the variable is shared with the whole session
              "txn"  : the variable is shared with the transaction
                       (request and response)
              "req"  : the variable is shared only during request
                       processing
              "res"  : the variable is shared only during response
                       processing
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9'
            and '_'.
 
<expr>      Is a standard HAProxy expression formed by a sample-fetch
            followed by some converters.

Example:

http-request set-var(req.my_var) req.fhdr(user-agent),lower

[ { if | unless } ]

This action is used to trigger sending of a group of SPOE messages. To do so,
the SPOE engine used to send messages must be defined, as well as the SPOE
group to send. Of course, the SPOE engine must refer to an existing SPOE
filter. If not engine name is provided on the SPOE filter line, the SPOE
agent name must be used.

Arguments:

<engine-name>  The SPOE engine name.
 
<group-name>   The SPOE group name as specified in the engine
               configuration.

http-request silent-drop [ { if | unless } ]

This stops the evaluation of the rules and makes the client-facing connection
suddenly disappear using a system-dependent way that tries to prevent the
client from being notified. The effect it then that the client still sees an
established connection while there's none on HAProxy. The purpose is to
achieve a comparable effect to "tarpit" except that it doesn't use any local
resource at all on the machine running HAProxy. It can resist much higher
loads than "tarpit", and slow down stronger attackers. It is important to
understand the impact of using this mechanism. All stateful equipment placed
between the client and HAProxy (firewalls, proxies, load balancers) will also
keep the established connection for a long time and may suffer from this
action.
On modern Linux systems running with enough privileges, the TCP_REPAIR socket
option is used to block the emission of a TCP reset. On other systems, the
socket's TTL is reduced to 1 so that the TCP reset doesn't pass the first
router, though it's still delivered to local networks. Do not use it unless
you fully understand how it works.

[deny_status ] [ { if | unless } ]

This stops the evaluation of the rules and immediately blocks the request
without responding for a delay specified by "timeout tarpit" or
"" if the former is not set. After that delay, if the client
is still connected, an HTTP error 500 (or optionally the status code
specified as an argument to "deny_status") is returned so that the client
does not suspect it has been tarpitted. Logs will report the flags "PT".
The goal of the tarpit rule is to slow down robots during an attack when
they're limited on the number of concurrent requests. It can be very
efficient against very dumb robots, and will significantly reduce the load
on firewalls compared to a "deny" rule. But when facing "correctly"
developed robots, it can make things worse by forcing haproxy and the front
firewall to support insane number of concurrent connections.
See also the "silent-drop" action.

http-request track-sc0 [table

] [ { if | unless } ]

[table

] [ { if | unless } ]

http-request track-sc2 [table

] [ { if | unless } ]

This enables tracking of sticky counters from current request. These rules do
not stop evaluation and do not change default action. The number of counters
that may be simultaneously tracked by the same connection is set in
MAX_SESS_STKCTR at build time (reported in haproxy -vv) which defaults to 3,
so the track-sc number is between 0 and (MAX_SESS_STCKTR-1). The first
"track-sc0" rule executed enables tracking of the counters of the specified
table as the first set. The first "track-sc1" rule executed enables tracking
of the counters of the specified table as the second set. The first
"track-sc2" rule executed enables tracking of the counters of the specified
table as the third set. It is a recommended practice to use the first set of
counters for the per-frontend counters and the second set for the per-backend
ones. But this is just a guideline, all may be used everywhere.

Arguments :

<key>   is mandatory, and is a sample expression rule as described in
        . It describes what elements of the incoming request or
        connection will be analyzed, extracted, combined, and used to
        select which table entry to update the counters.
 
<table> is an optional table to be used instead of the default one, which
        is the stick-table declared in the current proxy. All the counters
        for the matches and updates for the key will then be performed in
        that table until the session ends.

Once a "track-sc*" rule is executed, the key is looked up in the table and if
it is not found, an entry is allocated for it. Then a pointer to that entry
is kept during all the session's life, and this entry's counters are updated
as often as possible, every time the session's counters are updated, and also
systematically when the session ends. Counters are only updated for events
that happen after the tracking has been started. As an exception, connection
counters and request counters are systematically updated so that they reflect
useful information.
 
If the entry tracks concurrent connection counters, one connection is counted
for as long as the entry is tracked, and the entry will not expire during
that time. Tracking counters also provides a performance advantage over just
checking the keys, because only one table lookup is performed for all ACL
checks that make use of it.

http-request unset-var() [ { if | unless } ]

This is used to unset a variable. See above for details about <var-name>.

Example:

http-request unset-var(req.my_var)

[ { if | unless } ]

This directive executes the configured HTTP service to reply to the request
and stops the evaluation of the rules. An HTTP service may choose to reply by
sending any valid HTTP response or it may immediately close the connection
without sending any response. Outside natives services, for instance the
Prometheus exporter, it is possible to write your own services in Lua. No
further "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
" rules are evaluated.

Arguments :

<service-name>  is mandatory. It is the service to call

Example:

http-request use-service prometheus-exporter if { path /metrics }

[ { if | unless } ]

This will delay the processing of the request until the SSL handshake
happened. This is mostly useful to delay processing early data until we're
sure they are valid.

http-response [ { if | unless } ]

Access control for Layer 7 responses

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

The http-response statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Any rule may optionally be
followed by an ACL-based condition, in which case it will only be evaluated
if the condition is true. Since these rules apply on responses, the backend
rules are applied first, followed by the frontend's rules.
 
The first keyword is the rule's action. The supported actions are described
below.
 
There is no limit to the number of http-response statements per instance.
It is important to know that http-response rules are processed very early in
the HTTP processing, before "" or "rsprep" or "" rules. That way,
headers added by "add-header"/"set-header" are visible by almost all further
ACL rules.
 
Using "rspadd"/""/"rsprep" to manipulate request headers is discouraged
in newer versions (>= 1.5). But if you need to use regular expression to
delete headers, you can still use "". Also please use
"http-response deny" instead of "".

Example:

acl key_acl res.hdr(X-Acl-Key) -m found
acl myhost hdr(Host) -f myhost.lst
http-response add-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl
http-response del-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl

Example:

acl value  res.hdr(X-Value) -m found
use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }
http-response set-map(map.lst) %[src] %[res.hdr(X-Value)] if value
http-response del-map(map.lst) %[src]                     if ! value

See also : “http-request

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, about userlists and section 7 about ACL usage.

() [ { if | unless } ]

This is used to add a new entry into an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the new entry. It performs a lookup
in the ACL before insertion, to avoid duplicated (or more) values.
This lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "add acl" command from the stats socket, but can
be triggered by an HTTP response.

http-response add-header [ { if | unless } ]

This appends an HTTP header field whose name is specified in <name> and whose
value is defined by <fmt> which follows the log-format rules (see Custom Log
Format in ). This may be used to send a cookie to a client for
example, or to pass some internal information.
This rule is not final, so it is possible to add other similar rules.
Note that header addition is performed immediately, so one rule might reuse
the resulting header from a previous rule.

http-response allow [ { if | unless } ]

This stops the evaluation of the rules and lets the response pass the check.
No further "
This keyword is available in sections :
Proxy section
" rules are evaluated for the current section.

http-response cache-store [ { if | unless } ]

See  about cache setup.

http-response capture id [ { if | unless } ]

This captures sample expression <sample> from the response buffer, and
converts it to a string. The resulting string is stored into the next request
"" slot, so it will possibly appear next to some captured HTTP
headers. It will then automatically appear in the logs, and it will be
possible to extract it using sample fetch rules to feed it into headers or
anything. Please check section 7.3 (Fetching samples) and
"" for more information.
 
The keyword "id
This keyword is available in sections :
Bind options
" is the id of the capture slot which is used for storing the
string. The capture slot must be defined in an associated frontend.
This is useful to run captures in backends. The slot id can be declared by a
previous directive "http-response capture" or with the ""
keyword.
 
When using this action in a backend, double check that the relevant
frontend(s) have the required capture slots otherwise, this rule will be
ignored at run time. This can't be detected at configuration parsing time
due to HAProxy's ability to dynamically resolve backend name at runtime.

http-response del-acl() [ { if | unless } ]

This is used to delete an entry from an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It is the equivalent of the "del acl" command from the stats socket, but can
be triggered by an HTTP response.

[ { if | unless } ]

This removes all HTTP header fields whose name is specified in <name>.

http-response del-map() [ { if | unless } ]

This is used to delete an entry from a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It takes one argument: "file name" It is the equivalent of the "del map"
command from the stats socket, but can be triggered by an HTTP response.

[ { if | unless } ]

This stops the evaluation of the rules and immediately rejects the response
and emits an HTTP 502 error. No further "http-response
This keyword is available in sections :
Alphabetically sorted keywords reference
" rules are evaluated.

[ { if | unless } ]

This performs an HTTP redirection based on a redirect rule.
This supports a format string similarly to "http-request redirect" rules,
with the exception that only the "location" type of redirect is possible on
the response. See the "" keyword for the rule's syntax. When a
redirect rule is applied during a response, connections to the server are
closed so that no data can be forwarded from the server to the client.

http-response replace-header [ { if | unless } ]

This works like "" except that it works on the
server's response instead of the client's request.

Example:

http-response replace-header Set-Cookie (C=[^;]*);(.*) \1;ip=%bi;\2
# applied to:
Set-Cookie: C=1; expires=Tue, 14-Jun-2016 01:40:45 GMT
# outputs:
Set-Cookie: C=1;ip=192.168.1.20; expires=Tue, 14-Jun-2016 01:40:45 GMT
# assuming the backend IP is 192.168.1.20.

http-response replace-value [ { if | unless } ]

This works like "" except that it works on the
server's response instead of the client's request.

Example:

http-response replace-value Cache-control ^public$ private
# applied to:
Cache-Control: max-age=3600, public
# outputs:
Cache-Control: max-age=3600, private

http-response sc-inc-gpc0() [ { if | unless } ]

() [ { if | unless } ]

This action increments the GPC0 or GPC1 counter according with the sticky
counter designated by <sc-id>. If an error occurs, this action silently fails
and the actions evaluation continues.

http-response sc-set-gpt0() [ { if | unless } ]

This action sets the GPT0 tag according to the sticky counter designated by
<sc-id> and the value of <int>. The expected result is a boolean. If an error
occurs, this action silently fails and the actions evaluation continues.

[ { if | unless } ]

This action is used to trigger sending of a group of SPOE messages. To do so,
the SPOE engine used to send messages must be defined, as well as the SPOE
group to send. Of course, the SPOE engine must refer to an existing SPOE
filter. If not engine name is provided on the SPOE filter line, the SPOE
agent name must be used.

Arguments:

<engine-name>  The SPOE engine name.
 
<group-name>   The SPOE group name as specified in the engine
               configuration.

http-response set-header [ { if | unless } ]

This does the same as "add-header" except that the header name is first
removed if it existed. This is useful when passing security information to
the server, where the header must not be manipulated by external users.

[ { if | unless } ]

This is used to change the log level of the current request when a certain
condition is met. Valid levels are the 8 syslog levels (see the "log
This keyword is available in sections :
Alphabetically sorted keywords reference
"
keyword) plus the special level "silent" which disables logging for this
request. This rule is not final so the last matching rule wins. This rule can
be useful to disable health checks coming from another equipment.

()

This is used to add a new entry into a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes 2 arguments: <key fmt>, which follows
log-format rules, used to collect MAP key, and <value fmt>, which follows
log-format rules, used to collect content for the new entry. It performs a
lookup in the MAP before insertion, to avoid duplicated (or more) values.
This lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "set map" command from the stats socket, but can
be triggered by an HTTP response.

http-response set-mark [ { if | unless } ]

[ { if | unless } ]

This sets the "nice" factor of the current request being processed.
It only has effect against the other requests being processed at the same
time. The default value is 0, unless altered by the "" setting on the
"bind
This keyword is available in sections :
Alphabetically sorted keywords reference
" line. The accepted range is -1024..1024. The higher the value, the
nicest the request will be. Lower values will make the request more important
than other ones. This can be useful to improve the speed of some requests, or
lower the priority of non-important requests. Using this setting without
prior experimentation can cause some major slowdown.

[reason ] [ { if | unless } ]

This replaces the response status code with <status> which must be an integer
between 100 and 999. Optionally, a custom reason text can be provided defined
by <str>, or the default reason for the specified code will be used as a
fallback.

Example:

# return "431 Request Header Fields Too Large"
http-response set-status 431
# return "503 Slow Down", custom reason
http-response set-status 503 reason "Slow Down".

http-response set-tos [ { if | unless } ]

This is used to set the TOS or DSCP field value of packets sent to the client
to the value passed in <tos> on platforms which support this.
This value represents the whole 8 bits of the IP TOS field, and can be
expressed both in decimal or hexadecimal format (prefixed by "0x"). Note that
only the 6 higher bits are used in DSCP or TOS, and the two lower bits are
always 0. This can be used to adjust some routing behavior on border routers
based on some information from the request.
 
See RFC 2474, 2597, 3260 and 4594 for more information.

() [ { if | unless } ]

This is used to set the contents of a variable. The variable is declared
inline.

Arguments:

<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed are:
              "proc" : the variable is shared with the whole process
              "sess" : the variable is shared with the whole session
              "txn"  : the variable is shared with the transaction
                       (request and response)
              "req"  : the variable is shared only during request
                       processing
              "res"  : the variable is shared only during response
                       processing
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9', '.'
            and '_'.
 
<expr>      Is a standard HAProxy expression formed by a sample-fetch
            followed by some converters.

Example:

http-response set-var(sess.last_redir) res.hdr(location)

[ { if | unless } ]

This stops the evaluation of the rules and makes the client-facing connection
suddenly disappear using a system-dependent way that tries to prevent the
client from being notified. The effect it then that the client still sees an
established connection while there's none on HAProxy. The purpose is to
achieve a comparable effect to "tarpit" except that it doesn't use any local
resource at all on the machine running HAProxy. It can resist much higher
loads than "tarpit", and slow down stronger attackers. It is important to
understand the impact of using this mechanism. All stateful equipment placed
between the client and HAProxy (firewalls, proxies, load balancers) will also
keep the established connection for a long time and may suffer from this
action.
On modern Linux systems running with enough privileges, the TCP_REPAIR socket
option is used to block the emission of a TCP reset. On other systems, the
socket's TTL is reduced to 1 so that the TCP reset doesn't pass the first
router, though it's still delivered to local networks. Do not use it unless
you fully understand how it works.

http-response track-sc0 [table

] [ { if | unless } ]

[table

] [ { if | unless } ]

http-response track-sc2 [table

] [ { if | unless } ]

This enables tracking of sticky counters from current response. Please refer
to "http-request track-sc" for a complete description. The only difference
from "http-request track-sc" is the <key> sample expression can only make use
of samples in response (e.g. res.*, status etc.) and samples below Layer 6
(e.g. SSL-related samples, see ). If the sample is not
supported, haproxy will fail and warn while parsing the config.

http-response unset-var() [ { if | unless } ]

This is used to unset a variable. See "" for details
about <var-name>.

Example:

http-response unset-var(sess.last_redir)

http-reuse { never | safe | aggressive | always }

Declare how idle HTTP connections may be shared between requests

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

By default, a connection established between haproxy and the backend server
which is considered safe for reuse is moved back to the server's idle
connections pool so that any other request can make use of it. This is the
"safe" strategy below.
 
The argument indicates the desired connection reuse strategy :
 
  - "never"  : idle connections are never shared between sessions. This mode
               may be enforced to cancel a different strategy inherited from
               a defaults section or for troubleshooting. For example, if an
               old bogus application considers that multiple requests over
               the same connection come from the same client and it is not
               possible to fix the application, it may be desirable to
               disable connection sharing in a single backend. An example of
               such an application could be an old haproxy using cookie
               insertion in tunnel mode and not checking any request past the
               first one.
 
  - "safe"   : this is the default and the recommended strategy. The first
               request of a session is always sent over its own connection,
               and only subsequent requests may be dispatched over other
               existing connections. This ensures that in case the server
               closes the connection when the request is being sent, the
               browser can decide to silently retry it. Since it is exactly
               equivalent to regular keep-alive, there should be no side
               effects.
 
  - "aggressive" : this mode may be useful in webservices environments where
               all servers are not necessarily known and where it would be
               appreciable to deliver most first requests over existing
               connections. In this case, first requests are only delivered
               over existing connections that have been reused at least once,
               proving that the server correctly supports connection reuse.
               It should only be used when it's sure that the client can
               retry a failed request once in a while and where the benefit
               of aggressive connection reuse significantly outweighs the
               downsides of rare connection failures.
 
  - "always" : this mode is only recommended when the path to the server is
               known for never breaking existing connections quickly after
               releasing them. It allows the first request of a session to be
               sent to an existing connection. This can provide a significant
               performance increase over the "safe" strategy when the backend
               is a cache farm, since such components tend to show a
               consistent behavior and will benefit from the connection
               sharing. It is recommended that the "" timeout
               remains low in this mode so that no dead connections remain
               usable. In most cases, this will lead to the same performance
               gains as "aggressive" but with more risks. It should only be
               used when it improves the situation over "aggressive".
 
When http connection sharing is enabled, a great care is taken to respect the
connection properties and compatibility. Specifically :
  - connections made with "usesrc" followed by a client-dependent value
    ("client", "clientip", "hdr_ip") are marked private and never shared;
 
  - connections sent to a server with a TLS SNI extension are marked private
    and are never shared;
 
  - connections with certain bogus authentication schemes (relying on the
    connection) like NTLM are detected, marked private and are never shared;
 
A connection pool is involved and configurable with "".
 
Note: connection reuse improves the accuracy of the "server maxconn" setting,
because almost no new connection will be established while idle connections
remain available. This is particularly true with the "always" strategy.

See also : “option http-keep-alive“, “server maxconn”

[

]

Add the server name to a request. Use the header string given by <header>

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<header>  The header string to use to send the server name

The "http-send-name-header" statement causes the header field named <header>
to be set to the name of the target server at the moment the request is about
to be sent on the wire. Any existing occurrences of this header are removed.
Upon retries and redispatches, the header field is updated to always reflect
the server being attempted to connect to. Given that this header is modified
very late in the connection setup, it may have unexpected effects on already
modified headers. For example using it with transport-level header such as
connection, content-length, transfer-encoding and so on will likely result in
invalid requests being sent to the server. Additionally it has been reported
that this directive is currently being used as a way to overwrite the Host
header field in outgoing requests; while this trick has been known to work
as a side effect of the feature for some time, it is not officially supported
and might possibly not work anymore in a future version depending on the
technical difficulties this feature induces. A long-term solution instead
consists in fixing the application which required this trick so that it binds
to the correct host name.

See also : “

• This keyword is available in sections :
• Peers

“

id

Set a persistent ID to a proxy.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments : none

Set a persistent ID for the proxy. This ID must be unique and positive.
An unused ID will automatically be assigned if unset. The first assigned
value will be 1. This ID is currently only returned in statistics.

{ if | unless }

Declare a condition to ignore persistence

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

By default, when cookie persistence is enabled, every requests containing
the cookie are unconditionally persistent (assuming the target server is up
and running).
 
The "ignore-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore persistence.
This is sometimes useful to load balance requests for static files, which
often don't require persistence. This can also be used to fully disable
persistence for a specific User-Agent (for example, some web crawler bots).
 
The persistence is ignored when an "if" condition is met, or unless an
"unless" condition is met.

Example:

acl url_static  path_end         .gif .png .jpg .css .js
ignore-persist  if url_static

See also : ““, “cookie

• This keyword is available in sections :
• Server and default-server options

“, and section 7 about ACL usage.

{ global | local | none }

Allow seamless reload of HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

This directive points HAProxy to a file where server state from previous
running process has been saved. That way, when starting up, before handling
traffic, the new process can apply old states to servers exactly has if no
reload occurred. The purpose of the "load-server-state-from-file" directive is
to tell haproxy which file to use. For now, only 2 arguments to either prevent
loading state or load states from a file containing all backends and servers.
The state file can be generated by running the command "show servers state"
over the stats socket and redirect output.
 
The format of the file is versioned and is very specific. To understand it,
please read the documentation of the "show servers state" command (chapter
9.3 of Management Guide).

Arguments:

global     load the content of the file pointed by the global directive
           named "".
 
local      load the content of the file pointed by the directive
           "server-state-file-name" if set. If not set, then the backend
           name is used as a file name.
 
none       don't load any stat for this backend

Notes:
  - server's IP address is preserved across reloads by default, but the
    order can be changed thanks to the server's "" setting. This
    means that an IP address change performed on the CLI at run time will
    be preserved, and that any change to the local resolver (e.g. /etc/hosts)
    will possibly not have any effect if the state file is in use.
 
  - server's weight is applied from previous running process unless it has
    has changed between previous and new configuration files.

Example:

Minimal configuration
global
 stats socket /tmp/socket
 server-state-file /tmp/server_state
defaults
 load-server-state-from-file global
backend bk
 server s1 127.0.0.1:22 check weight 11
 server s2 127.0.0.1:22 check weight 12

Then one can run :
 
  socat /tmp/socket - <<< "show servers state" > /tmp/server_state
 
Content of the file /tmp/server_state would be like this:
 
  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0

Example:

Minimal configuration
global
 stats socket /tmp/socket
 server-state-base /etc/haproxy/states
defaults
 load-server-state-from-file local
backend bk
 server s1 127.0.0.1:22 check weight 11
 server s2 127.0.0.1:22 check weight 12

Then one can run :
 
  socat /tmp/socket - <<< "show servers state bk" > /etc/haproxy/states/bk
 
Content of the file /etc/haproxy/states/bk would be like this:
 
  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0

See also: “server-state-file“, ““, and “show servers state”

log global

[len ] [format ] [sample :] [ []]

no log

Enable per-instance logging of events and traffic.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Prefix :
  no         should be used when the logger list must be flushed. For example,
             if you don't want to inherit from the default logger list. This
             prefix does not allow arguments.

Arguments :

global     should be used when the instance's logging parameters are the
           same as the global ones. This is the most common usage. "global"
           replaces <address>, <facility> and <level> with those of the log
           entries found in the "global" section. Only one ""
           statement may be used per instance, and this form takes no other
           parameter.
 
<address>  indicates where to send the logs. It takes the same format as
           for the "global" section's logs, and can be one of :
 
           - An IPv4 address optionally followed by a colon (':') and a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).
 
           - An IPv6 address followed by a colon (':') and optionally a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).
 
           - A filesystem path to a UNIX domain socket, keeping in mind
             considerations for chroot (be sure the path is accessible
             inside the chroot) and uid/gid (be sure the path is
             appropriately writable).
 
           - A file descriptor number in the form "fd@<number>", which may
             point to a pipe, terminal, or socket. In this case unbuffered
             logs are used and one writev() call per log is performed. This
             is a bit expensive but acceptable for most workloads. Messages
             sent this way will not be truncated but may be dropped, in
             which case the DroppedLogs counter will be incremented. The
             writev() call is atomic even on pipes for messages up to
             PIPE_BUF size, which POSIX recommends to be at least 512 and
             which is 4096 bytes on most modern operating systems. Any
             larger message may be interleaved with messages from other
             processes.  Exceptionally for debugging purposes the file
             descriptor may also be directed to a file, but doing so will
             significantly slow haproxy down as non-blocking calls will be
             ignored. Also there will be no way to purge nor rotate this
             file without restarting the process. Note that the configured
             syslog format is preserved, so the output is suitable for use
             with a TCP syslog server. See also the "short" and "raw"
             formats below.
 
           - "stdout" / "stderr", which are respectively aliases for "fd@1"
             and "fd@2", see above.
 
           You may want to reference some environment variables in the
           address parameter, see section 2.3 about environment variables.
 
<length>   is an optional maximum line length. Log lines larger than this
           value will be truncated before being sent. The reason is that
           syslog servers act differently on log line length. All servers
           support the default value of 1024, but some servers simply drop
           larger lines while others do log them. If a server supports long
           lines, it may make sense to set this value here in order to avoid
           truncating long lines. Similarly, if a server drops long lines,
           it is preferable to truncate them before sending them. Accepted
           values are 80 to 65535 inclusive. The default value of 1024 is
           generally fine for all standard usages. Some specific cases of
           long captures or JSON-formatted logs may require larger values.
 
<ranges>   A list of comma-separated ranges to identify the logs to sample.
           This is used to balance the load of the logs to send to the log
           server. The limits of the ranges cannot be null. They are numbered
           from 1. The size or period (in number of logs) of the sample must
           be set with <sample_size> parameter.
 
<sample_size>
           The size of the sample in number of logs to consider when balancing
           their logging loads. It is used to balance the load of the logs to
           send to the syslog server. This size must be greater or equal to the
           maximum of the high limits of the ranges.
           (see also <ranges> parameter).
 
<format> is the log format used when generating syslog messages. It may be
         one of the following :
 
  rfc3164   The RFC3164 syslog message format. This is the default.
            (https://tools.ietf.org/html/rfc3164)
 
  rfc5424   The RFC5424 syslog message format.
            (https://tools.ietf.org/html/rfc5424)
 
  short     A message containing only a level between angle brackets such as
            '<3>', followed by the text. The PID, date, time, process name
            and system name are omitted. This is designed to be used with a
            local log server. This format is compatible with what the
            systemd logger consumes.
 
  raw       A message containing only the text. The level, PID, date, time,
            process name and system name are omitted. This is designed to
            be used in containers or during development, where the severity
            only depends on the file descriptor used (stdout/stderr).
 
<facility> must be one of the 24 standard syslog facilities :
 
               kern   user   mail   daemon auth   syslog lpr    news
               uucp   cron   auth2  ftp    ntp    audit  alert  cron2
               local0 local1 local2 local3 local4 local5 local6 local7
 
           Note that the facility is ignored for the "short" and "raw"
           formats, but still required as a positional field. It is
           recommended to use "" in this case to make it clear that
           it's only supposed to be used locally.
 
<level>    is optional and can be specified to filter outgoing messages. By
           default, all messages are sent. If a level is specified, only
           messages with a severity at least as important as this level
           will be sent. An optional minimum level can be specified. If it
           is set, logs emitted with a more severe level than this one will
           be capped to this level. This is used to avoid sending "emerg"
           messages on all terminals on some default syslog configurations.
           Eight levels are known :
 
             emerg  alert  crit   err    warning notice info  debug

It is important to keep in mind that it is the frontend which decides what to
log from a connection, and that in case of content switching, the log entries
from the backend will be ignored. Connections are logged at level "info".
 
However, backend log declaration define how and where servers status changes
will be logged. Level "notice" will be used to indicate a server going up,
"warning" will be used for termination signals and definitive service
termination, and "alert" will be used for when a server goes down.
 
Note : According to RFC3164, messages are truncated to 1024 bytes before
       being emitted.

Example :

log global
log stdout format short daemon          # send log to systemd
log stdout format raw daemon            # send everything to stdout
log stderr format raw daemon notice     # send important events to stderr
log 127.0.0.1:514 local0 notice         # only send important events
log 127.0.0.1:514 local0 notice notice  # same but limit output level
log "${LOCAL_SYSLOG}:514" local0 notice   # send to local server

log-format

Specifies the log format string to use for traffic logs

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

This directive specifies the log format string that will be used for all logs
resulting from traffic passing through the frontend using this line. If the
directive is used in a defaults section, all subsequent frontends will use
the same log format. Please see  which covers the log format
string in depth.
 
"log-format" directive overrides previous "", "log-format" and
"" directives.

log-format-sd

Specifies the RFC5424 structured-data log format string

defaults	frontend	listen	backend
yes	yes	yes	no

This directive specifies the RFC5424 structured-data log format string that
will be used for all logs resulting from traffic passing through the frontend
using this line. If the directive is used in a defaults section, all
subsequent frontends will use the same log format. Please see 
which covers the log format string in depth.
 
See https://tools.ietf.org/html/rfc5424#section-6.3 for more information
about the RFC5424 structured-data part.
 
Note : This log format string will be used only for loggers that have set
       log format to "rfc5424".

Example :

log-format-sd [exampleSDID@1234\ bytes=\"%B\"\ status=\"%ST\"]

log-tag

Specifies the log tag to use for all outgoing logs

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Sets the tag field in the syslog header to this string. It defaults to the
log-tag set in the global section, otherwise the program name as launched
from the command line, which usually is "haproxy". Sometimes it can be useful
to differentiate between multiple processes running on the same host, or to
differentiate customer instances running in the same process. In the backend,
logs about servers up/down will use this tag. As a hint, it can be convenient
to set a log-tag related to a hosted customer in a defaults section then put
all the frontends and backends for that customer, then start another customer
in a new defaults section. See also the global "
This keyword is available in sections :
Process management and security
" directive.

max-keep-alive-queue

Set the maximum server queue size for maintaining keep-alive connections

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

HTTP keep-alive tries to reuse the same server connection whenever possible,
but sometimes it can be counter-productive, for example if a server has a lot
of connections while other ones are idle. This is especially true for static
servers.
 
The purpose of this setting is to set a threshold on the number of queued
connections at which haproxy stops trying to reuse the same server and prefers
to find another one. The default value, -1, means there is no limit. A value
of zero means that keep-alive requests will never be queued. For very close
servers which can be reached with a low latency and which are not sensible to
breaking keep-alive, a low value is recommended (e.g. local static server can
use a value of 10 or less). For remote servers suffering from a high latency,
higher values might be needed to cover for the latency and/or the cost of
picking a different server.
 
Note that this has no impact on responses which are maintained to the same
server consecutively to a 401 response. They will still go to the same server
even if they have to be queued.

See also : ““, “option prefer-last-server“, server “

• This keyword is available in sections :
• Performance tuning
• Bind options

“ and cookie persistence.

max-session-srv-conns

Set the maximum number of outgoing connections we can keep idling for a given
client session. The default is 5 (it precisely equals MAX_SRV_LIST which is
defined at build time).

Fix the maximum number of concurrent connections on a frontend

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<conns>   is the maximum number of concurrent connections the frontend will
          accept to serve. Excess connections will be queued by the system
          in the socket's listen queue and will be served once a connection
          closes.

If the system supports it, it can be useful on big sites to raise this limit
very high so that haproxy manages connection queues, instead of leaving the
clients with unanswered connection attempts. This value should not exceed the
global maxconn. Also, keep in mind that a connection contains two buffers
of tune.bufsize (16kB by default) each, as well as some other data resulting
in about 33 kB of RAM being consumed per established connection. That means
that a medium system equipped with 1GB of RAM can withstand around
20000-25000 concurrent connections if properly tuned.
 
Also, when <conns> is set to large values, it is possible that the servers
are not sized to accept such loads, and for this reason it is generally wise
to assign them some reasonable connection limits.
 
When this value is set to zero, which is the default, the global "maxconn
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options
"
value is used.

See also : “

• This keyword is available in sections :
• Peers

“, global section’s “maxconn

• This keyword is available in sections :
• Alphabetically sorted keywords reference
• Server and default-server options

“, ““

mode { tcp|http|health }

Set the running mode or protocol of the instance

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

tcp       The instance will work in pure TCP mode. A full-duplex connection
          will be established between clients and servers, and no layer 7
          examination will be performed. This is the default mode. It
          should be used for SSL, SSH, SMTP, ...
 
http      The instance will work in HTTP mode. The client request will be
          analyzed in depth before connecting to any server. Any request
          which is not RFC-compliant will be rejected. Layer 7 filtering,
          processing and switching will be possible. This is the mode which
          brings HAProxy most of its value.
 
health    The instance will work in "health" mode. It will just reply "OK"
          to incoming connections and close the connection. Alternatively,
          If the "" option is set, "HTTP/1.0 200 OK" will be sent
          instead. Nothing will be logged in either case. This mode is used
          to reply to external components health checks. This mode is
          deprecated and should not be used anymore as it is possible to do
          the same and even better by combining TCP or HTTP modes with the
          "monitor" keyword.

When doing content switching, it is mandatory that the frontend and the
backend are in the same mode (generally HTTP), otherwise the configuration
will be refused.

Example :

defaults http_instances
    mode http

See also : ““, “monitor-net“

{ if | unless }

Add a condition to report a failure to a monitor HTTP request.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

if <cond>     the monitor request will fail if the condition is satisfied,
              and will succeed otherwise. The condition should describe a
              combined test which must induce a failure if all conditions
              are met, for instance a low number of servers both in a
              backend and its backup.
 
unless <cond> the monitor request will succeed only if the condition is
              satisfied, and will fail otherwise. Such a condition may be
              based on a test on the presence of a minimum number of active
              servers in a list of backends.

This statement adds a condition which can force the response to a monitor
request to report a failure. By default, when an external component queries
the URI dedicated to monitoring, a 200 response is returned. When one of the
conditions above is met, haproxy will return 503 instead of 200. This is
very useful to report a site failure to an external component which may base
routing advertisements between multiple sites on the availability reported by
haproxy. In this case, one would rely on an ACL involving the "nbsrv
This keyword is available in sections :
Fetching samples from internal states
"
criterion. Note that "" only works in HTTP mode. Both status
messages may be tweaked using "errorfile" or "" if needed.

Example:

frontend www
   mode http
   acl site_dead nbsrv(dynamic) lt 2
   acl site_dead nbsrv(static)  lt 2
   monitor-uri   /site_alive
   monitor fail  if site_dead

See also : “monitor-net“, ““, “errorfile“, ““

monitor-net

Declare a source network which is limited to monitor requests

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<source>  is the source IPv4 address or network which will only be able to
          get monitor responses to any request. It can be either an IPv4
          address, a host name, or an address followed by a slash ('/')
          followed by a mask.

In TCP mode, any connection coming from a source matching <source> will cause
the connection to be immediately closed without any log. This allows another
equipment to probe the port and verify that it is still listening, without
forwarding the connection to a remote server.
 
In HTTP mode, a connection coming from a source matching <source> will be
accepted, the following response will be sent without waiting for a request,
then the connection will be closed : "HTTP/1.0 200 OK". This is normally
enough for any front-end HTTP probe to detect that the service is UP and
running without forwarding the request to a backend server. Note that this
response is sent in raw format, without any transformation. This is important
as it means that it will not be SSL-encrypted on SSL listeners.
 
Monitor requests are processed very early, just after tcp-request connection
ACLs which are the only ones able to block them. These connections are short
lived and never wait for any data from the client. They cannot be logged, and
it is the intended purpose. They are only used to report HAProxy's health to
an upper component, nothing more. Please note that "" rules do
not apply to connections intercepted by "monitor-net".
 
Last, please note that only one "" statement can be specified in
a frontend. If more than one is found, only the last one will be considered.

Example :

# addresses .252 and .253 are just probing us.
frontend www
    monitor-net 192.168.0.252/31

See also : “monitor fail“, ““

monitor-uri

Intercept a URI used by external components' monitor requests

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<uri>     is the exact URI which we want to intercept to return HAProxy's
          health status instead of forwarding the request.

When an HTTP request referencing <uri> will be received on a frontend,
HAProxy will not forward it nor log it, but instead will return either
"HTTP/1.0 200 OK" or "HTTP/1.0 503 Service unavailable", depending on failure
conditions defined with "". This is normally enough for any
front-end HTTP probe to detect that the service is UP and running without
forwarding the request to a backend server. Note that the HTTP method, the
version and all headers are ignored, but the request must at least be valid
at the HTTP level. This keyword may only be used with an HTTP-mode frontend.
 
Monitor requests are processed very early, just after the request is parsed
and even before any "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
" or "" rulesets. The only rulesets
applied before are the tcp-request ones. They cannot be logged either, and it
is the intended purpose. They are only used to report HAProxy's health to an
upper component, nothing more. However, it is possible to add any number of
conditions using "monitor fail" and ACLs so that the result can be adjusted
to whatever check can be imagined (most often the number of available servers
in a backend).

Example :

# Use /haproxy_test to report haproxy's status
frontend www
    mode http
    monitor-uri /haproxy_test

See also : ““, “monitor-net“

no option abortonclose

Enable or disable early dropping of aborted requests pending in queues.

May be used in sections :

Arguments : none

In presence of very high loads, the servers will take some time to respond.
The per-instance connection queue will inflate, and the response time will
increase respective to the size of the queue times the average per-session
response time. When clients will wait for more than a few seconds, they will
often hit the "STOP" button on their browser, leaving a useless request in
the queue, and slowing down other users, and the servers as well, because the
request will eventually be served, then aborted at the first error
encountered while delivering the response.
 
As there is no way to distinguish between a full STOP and a simple output
close on the client side, HTTP agents should be conservative and consider
that the client might only have closed its output channel while waiting for
the response. However, this introduces risks of congestion when lots of users
do the same, and is completely useless nowadays because probably no client at
all will close the session while waiting for the response. Some HTTP agents
support this behavior (Squid, Apache, HAProxy), and others do not (TUX, most
hardware-based load balancers). So the probability for a closed input channel
to represent a user hitting the "STOP" button is close to 100%, and the risk
of being the single component to break rare but valid traffic is extremely
low, which adds to the temptation to be able to abort a session early while
still not served and not pollute the servers.
 
In HAProxy, the user can choose the desired behavior using the option
"". By default (without the option) the behavior is HTTP
compliant and aborted requests will be served. But when the option is
specified, a session with an incoming channel closed will be aborted while
it is still possible, either pending in the queue for a connection slot, or
during the connection establishment if the server has not yet acknowledged
the connection request. This considerably reduces the queue size and the load
on saturated servers when users are tempted to click on STOP, which in turn
reduces the response time for other users.
 
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “timeout queue“ and server’s “

• This keyword is available in sections :
• Performance tuning
• Bind options

“ and “maxqueue“ parameters

no option accept-invalid-http-request

Enable or disable relaxing of HTTP request parsing

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. Similarly, the
list of characters allowed to appear in a URI is well defined by RFC3986, and
chars 0-31, 32 (space), 34 ('"'), 60 ('<'), 62 ('>'), 92 ('\'), 94 ('^'), 96
('`'), 123 ('{'), 124 ('|'), 125 ('}'), 127 (delete) and anything above are
not allowed at all. HAProxy always blocks a number of them (0..32, 127). The
remaining ones are blocked by default unless this option is enabled. This
option also relaxes the test on the HTTP version, it allows HTTP/0.9 requests
to pass through (no version specified) and multiple digits for both the major
and the minor version.

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
requests, but the complete request will be captured in order to permit later
analysis using the "show errors" request on the UNIX stats socket. Similarly,
requests containing invalid chars in the URI part will be logged. Doing this
also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““ and “show errors” on the stats socket.

option accept-invalid-http-response

Enable or disable relaxing of HTTP response parsing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. This option also
relaxes the test on the HTTP version format, it allows multiple digits for
both the major and the minor version.

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
responses, but the complete response will be captured in order to permit
later analysis using the "show errors" request on the UNIX stats socket.
Doing this also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option accept-invalid-http-request“ and “show errors” on the stats socket.

no option allbackups

Use either all backup servers at a time or only the first one

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

By default, the first operational backup server gets all traffic when normal
servers are all down. Sometimes, it may be preferred to use multiple backups
at once, because one will not be enough. When "" is enabled,
the load balancing will be performed among all backup servers when all normal
ones are unavailable. The same load balancing algorithm will be used and the
servers' weights will be respected. Thus, there will not be any priority
order between the backup servers anymore.

This option is mostly used with static server farms dedicated to return a
"sorry" page when an application is completely offline.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

option checkcache

Analyze all server responses and block responses with cacheable cookies

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

Some high-level frameworks set application cookies everywhere and do not
always let enough control to the developer to manage how the responses should
be cached. When a session cookie is returned on a cacheable object, there is a
high risk of session crossing or stealing between users traversing the same
caches. In some situations, it is better to block the response than to let
some sensitive session information go in the wild.

The option "checkcache" enables deep inspection of all server responses for
strict compliance with HTTP specification in terms of cacheability. It
carefully checks "Cache-control", "Pragma" and "Set-cookie" headers in server
response to check if there's a risk of caching a cookie on a client-side
proxy. When this option is enabled, the only responses which can be delivered
to the client are :
  - all those without "Set-Cookie" header;
  - all those with a return code other than 200, 203, 204, 206, 300, 301,
    404, 405, 410, 414, 501, provided that the server has not set a
    "Cache-control: public" header field;
  - all those that result from a request using a method other than GET, HEAD,
    OPTIONS, TRACE, provided that the server has not set a 'Cache-Control:
    public' header field;
  - those with a 'Pragma: no-cache' header
  - those with a 'Cache-control: private' header
  - those with a 'Cache-control: no-store' header
  - those with a 'Cache-control: max-age=0' header
  - those with a 'Cache-control: s-maxage=0' header
  - those with a 'Cache-control: no-cache' header
  - those with a 'Cache-control: no-cache=""' header
  - those with a 'Cache-control: no-cache="set-cookie,' header
    (allowing other fields after set-cookie)

If a response doesn't respect these requirements, then it will be blocked
just as if it was from an "rspdeny" filter, with an "HTTP 502 bad gateway".
The session state shows "PH--" meaning that the proxy blocked the response
during headers processing. Additionally, an alert will be sent in the logs so
that admins are informed that there's something to be fixed.

Due to the high impact on the application, the application should be tested
in depth with the option enabled before going to production. It is also a
good practice to always activate it during tests, even if it is not used in
production, as it will report potentially dangerous application behaviors.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

no option clitcpka

Enable or disable the sending of TCP keepalive packets on the client side

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "" enables the emission of TCP keep-alive probes on the
client side of a connection, which should help when session expirations are
noticed between HAProxy and a client.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option srvtcpka“, ““

option contstats

Enable continuous traffic statistics updates

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

By default, counters used for statistics calculation are incremented
only when a session finishes. It works quite well when serving small
objects, but with big ones (for example large images or archives) or
with A/V streaming, a graph generated from haproxy counters looks like
a hedgehog. With this option enabled counters get incremented frequently
along the session, typically every 5 seconds, which is often enough to
produce clean graphs. Recounting touches a hotpath directly so it is not
not enabled by default, as it can cause a lot of wakeups for very large
session counts and cause a small performance drop.

no option dontlog-normal

Enable or disable logging of normal, successful connections

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

There are large sites dealing with several thousand connections per second
and for which logging is a major pain. Some of them are even forced to turn
logs off and cannot debug production issues. Setting this option ensures that
normal connections, those which experience no error, no timeout, no retry nor
redispatch, will not be logged. This leaves disk space for anomalies. In HTTP
mode, the response status code is checked and return codes 5xx will still be
logged.

It is strongly discouraged to use this option as most of the time, the key to
complex issues is in the normal logs which will not be logged here. If you
need to separate logs, see the "" option instead.

See also : “log

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, ““, “log-separate-errors“ and about logging.

option dontlognull

Enable or disable logging of null connections

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

In certain environments, there are components which will regularly connect to
various systems to ensure that they are still alive. It can be the case from
another load balancer as well as from monitoring systems. By default, even a
simple port probe or scan will produce a log. If those connections pollute
the logs too much, it is possible to enable option "dontlognull" to indicate
that a connection on which no data has been transferred will not be logged,
which typically corresponds to those probes. Note that errors will still be
returned to the client and accounted for in the stats. If this is not what is
desired, option http-ignore-probes can be used instead.

It is generally recommended not to use this option in uncontrolled
environments (e.g. internet), otherwise scans and other malicious activities
would not be logged.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “

• This keyword is available in sections :
• Process management and security

“, “http-ignore-probes“, ““, “monitor-uri“, and about logging.

option forwardfor [ except ] [ header ] [ if-none ]

Enable insertion of the X-Forwarded-For header to requests sent to servers

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<network> is an optional argument used to disable this option for sources
          matching <network>
<name>    an optional argument to specify a different "X-Forwarded-For"
          header name.

Since HAProxy works in reverse-proxy mode, the servers see its IP address as
their client address. This is sometimes annoying when the client's IP address
is expected in server logs. To solve this problem, the well-known HTTP header
"X-Forwarded-For" may be added by HAProxy to all requests sent to the server.
This header contains a value representing the client's IP address. Since this
header is always appended at the end of the existing header list, the server
must be configured to always use the last occurrence of this header only. See
the server's manual to find how to enable use of this standard header. Note
that only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.

The keyword "header" may be used to supply a different header name to replace
the default "X-Forwarded-For". This can be useful where you might already
have a "X-Forwarded-For" header from a different application (e.g. stunnel),
and you need preserve it. Also if your backend server doesn't use the
"X-Forwarded-For" header and requires different one (e.g. Zeus Web Servers
require "X-Cluster-Client-IP").

Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.

Alternatively, the keyword "if-none" states that the header will only be
added if it is not present. This should only be used in perfectly trusted
environment, as this might cause a security issue if headers reaching haproxy
are under the control of the end-user.

This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined. In the case of the "if-none" argument, if at least one of
the frontend or the backend does not specify it, it wants the addition to be
mandatory, so it wins.

Example :

# Public HTTP address also used by stunnel on the same machine
frontend www
    mode http
    option forwardfor except 127.0.0.1  # stunnel already adds the header

# Those servers want the IP Address in X-Client
backend www
    mode http
    option forwardfor header X-Client

See also : ““, “option http-server-close“, ““

option h1-case-adjust-bogus-client

Enable or disable the case adjustment of HTTP/1 headers sent to bogus clients

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

When HAProxy receives an HTTP/1 response, its header names are converted to
lower case and manipulated and sent this way to the clients. If a client is
known to violate the HTTP standards and to fail to process a response coming
from HAProxy, it is possible to transform the lower case header names to a
different format when the response is formatted and sent to the client, by
enabling this option and specifying the list of headers to be reformatted
using the global directives "h1-case-adjust" or "". This
must only be a temporary workaround for the time it takes the client to be
fixed, because clients which require such workarounds might be vulnerable to
content smuggling attacks and must absolutely be fixed.

Please note that this option will not affect standards-compliant clients.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also: “option h1-case-adjust-bogus-server“, ““, “h1-case-adjust-file“.

no option h1-case-adjust-bogus-server

Enable or disable the case adjustment of HTTP/1 headers sent to bogus servers

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

When HAProxy receives an HTTP/1 request, its header names are converted to
lower case and manipulated and sent this way to the servers. If a server is
known to violate the HTTP standards and to fail to process a request coming
from HAProxy, it is possible to transform the lower case header names to a
different format when the request is formatted and sent to the server, by
enabling this option and specifying the list of headers to be reformatted
using the global directives "" or "h1-case-adjust-file". This
must only be a temporary workaround for the time it takes the server to be
fixed, because servers which require such workarounds might be vulnerable to
content smuggling attacks and must absolutely be fixed.

Please note that this option will not affect standards-compliant servers.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also: ““, “h1-case-adjust“, ““.

option http-buffer-request

Enable or disable waiting for whole HTTP request body before proceeding

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

It is sometimes desirable to wait for the body of an HTTP request before
taking a decision. This is what is being done by "balance url_param" for
example. The first use case is to buffer requests from slow clients before
connecting to the server. Another use case consists in taking the routing
decision based on the request body's contents. This option placed in a
frontend or backend forces the HTTP processing to wait until either the whole
body is received, or the request buffer is full, or the first chunk is
complete in case of chunked encoding. It can have undesired side effects with
some applications abusing HTTP by expecting unbuffered transmissions between
the frontend and the backend, so this should definitely not be used by
default.

See also : ““, “timeout http-request“

no option http-ignore-probes

Enable or disable logging of null connections and request timeouts

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

Recently some browsers started to implement a "pre-connect" feature
consisting in speculatively connecting to some recently visited web sites
just in case the user would like to visit them. This results in many
connections being established to web sites, which end up in 408 Request
Timeout if the timeout strikes first, or 400 Bad Request when the browser
decides to close them first. These ones pollute the log and feed the error
counters. There was already "" but it's insufficient in
this case. Instead, this option does the following things :
   - prevent any 400/408 message from being sent to the client if nothing
     was received over a connection before it was closed;
   - prevent any log from being emitted in this situation;
   - prevent any error counter from being incremented

That way the empty connection is silently ignored. Note that it is better
not to use this unless it is clear that it is needed, because it will hide
real problems. The most common reason for not receiving a request and seeing
a 408 is due to an MTU inconsistency between the client and an intermediary
element such as a VPN, which blocks too large packets. These issues are
generally seen with POST requests as well as GET with large cookies. The logs
are often the only way to detect them.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “log

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, ““, “errorfile“, and about logging.

option http-keep-alive

Enable or disable HTTP keep-alive from client to server

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "" or "option http-tunnel".
This option allows to set back the keep-alive mode, which can be useful when
another mode was used in a defaults section.

Setting "" enables HTTP keep-alive mode on the client-
and server- sides. This provides the lowest latency on the client side (slow
network) and the fastest session reuse on the server side at the expense
of maintaining idle connections to the servers. In general, it is possible
with this option to achieve approximately twice the request rate that the
"http-server-close" option achieves on small objects. There are mainly two
situations where this option may be useful :

  - when the server is non-HTTP compliant and authenticates the connection
    instead of requests (e.g. NTLM authentication)

  - when the cost of establishing the connection to the server is significant
    compared to the cost of retrieving the associated object from the server.

This last case can happen when the server is a fast static server of cache.
In this case, the server will need to be properly tuned to support high enough
connection counts because connections will last until the client sends another
request.

If the client request has to go to another backend or another server due to
content switching or the load balancing algorithm, the idle connection will
immediately be closed and a new one re-opened. Option "" is
available to try optimize server selection so that if the server currently
attached to an idle connection is usable, it will be used.

At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "timeout http-keep-alive" or "" if
not set.

This option disables and replaces any previous "option httpclose", "option
http-server-close" or "". When backend and frontend options
differ, all of these 4 options have precedence over "option http-keep-alive".

See also : ““,, “option http-server-close“, ““, “option http-pretend-keepalive“, and “1.1. The HTTP transaction model”.

no option http-no-delay

Instruct the system to favor low interactive delays over performance in HTTP

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

In HTTP, each payload is unidirectional and has no notion of interactivity.
Any agent is expected to queue data somewhat for a reasonably low delay.
There are some very rare server-to-server applications that abuse the HTTP
protocol and expect the payload phase to be highly interactive, with many
interleaved data chunks in both directions within a single request. This is
absolutely not supported by the HTTP specification and will not work across
most proxies or servers. When such applications attempt to do this through
haproxy, it works but they will experience high delays due to the network
optimizations which favor performance by instructing the system to wait for
enough data to be available in order to only send full packets. Typical
delays are around 200 ms per round trip. Note that this only happens with
abnormal uses. Normal uses such as CONNECT requests nor WebSockets are not
affected.

When "" is present in either the frontend or the backend
used by a connection, all such optimizations will be disabled in order to
make the exchanges as fast as possible. Of course this offers no guarantee on
the functionality, as it may break at any other place. But if it works via
HAProxy, it will work as fast as possible. This option should never be used
by default, and should never be used at all unless such a buggy application
is discovered. The impact of using this option is an increase of bandwidth
usage and CPU usage, which may significantly lower performance in high
latency environments.

See also : “option http-buffer-request“

no option http-pretend-keepalive

Define whether haproxy will announce keepalive to the server or not

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When running with "" or "option httpclose", haproxy
adds a "Connection: close" header to the request forwarded to the server.
Unfortunately, when some servers see this header, they automatically refrain
from using the chunked encoding for responses of unknown length, while this
is totally unrelated. The immediate effect is that this prevents haproxy from
maintaining the client connection alive. A second effect is that a client or
a cache could receive an incomplete response without being aware of it, and
consider the response complete.

By setting "", haproxy will make the server
believe it will keep the connection alive. The server will then not fall back
to the abnormal undesired above. When haproxy gets the whole response, it
will close the connection with the server just as it would do with the
"option httpclose". That way the client gets a normal response and the
connection is correctly closed on the server side.

It is recommended not to enable this option by default, because most servers
will more efficiently close the connection themselves after the last packet,
and release its buffers slightly earlier. Also, the added packet on the
network could slightly reduce the overall peak performance. However it is
worth noting that when this option is enabled, haproxy will have slightly
less work to do. So if haproxy is the bottleneck on the whole architecture,
enabling this option might save a few CPU cycles.

This option may be set in backend and listen sections. Using it in a frontend
section will be ignored and a warning will be reported during startup. It is
a backend related option, so there is no real reason to set it on a
frontend. This option may be combined with "", which will
cause keepalive to be announced to the server and close to be announced to
the client. This practice is discouraged though.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option httpclose“, ““, and “option http-keep-alive“

no option http-server-close

Enable or disable HTTP connection closing on the server side

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "", "option httpclose" or "".
Setting "option http-server-close" enables HTTP connection-close mode on the
server side while keeping the ability to support HTTP keep-alive and
pipelining on the client side. This provides the lowest latency on the client
side (slow network) and the fastest session reuse on the server side to save
server resources, similarly to "".  It also permits
non-keepalive capable servers to be served in keep-alive mode to the clients
if they conform to the requirements of RFC7230. Please note that some servers
do not always conform to those requirements when they see "Connection: close"
in the request. The effect will be that keep-alive will never be used. A
workaround consists in enabling "option http-pretend-keepalive".

At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "" or "timeout http-request" if
not set.

This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
It disables and replaces any previous "", "option http-tunnel"
or "". Please check section 4 ("Proxies") to see how
this option combines with others when frontend and backend options differ.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““, “option http-pretend-keepalive“, ““, and “1.1. The HTTP transaction model”.

option http-tunnel (deprecated)

(deprecated)

Disable or enable HTTP connection processing after first transaction.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

Warning : Because it cannot work in HTTP/2, this option is deprecated and it
is only supported on legacy HTTP frontends. In HTX, it is ignored and a
warning is emitted during HAProxy startup.

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "" or "option http-tunnel".

Option "" disables any HTTP processing past the first request and
the first response. This is the mode which was used by default in versions
1.0 to 1.5-dev21. It is the mode with the lowest processing overhead, which
is normally not needed anymore unless in very specific cases such as when
using an in-house protocol that looks like HTTP but is not compatible, or
just to log one request per client in order to reduce log size. Note that
everything which works at the HTTP level, including header parsing/addition,
cookie processing or content switching will only work for the first request
and will be ignored after the first response.

This option may be set on frontend and listen sections. Using it on a backend
section will be ignored and a warning will be reported during the startup. It
is a frontend related option, so there is no real reason to set it on a
backend.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option httpclose“, ““, “option http-keep-alive“, and “1.1. The HTTP transaction model”.

no option http-use-proxy-header

Make use of non-standard Proxy-Connection header instead of Connection

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

While RFC7230 explicitly states that HTTP/1.1 agents must use the
Connection header to indicate their wish of persistent or non-persistent
connections, both browsers and proxies ignore this header for proxied
connections and make use of the undocumented, non-standard Proxy-Connection
header instead. The issue begins when trying to put a load balancer between
browsers and such proxies, because there will be a difference between what
haproxy understands and what the client and the proxy agree on.

By setting this option in a frontend, haproxy can automatically switch to use
that non-standard header if it sees proxied requests. A proxied request is
defined here as one where the URI begins with neither a '/' nor a '*'. This
is incompatible with the HTTP tunnel mode. Note that this option can only be
specified in a frontend and will affect the request along its whole life.

Also, when this option is set, a request which requires authentication will
automatically switch to use proxy authentication headers if it is itself a
proxied request. That makes it possible to check or enforce authentication in
front of an existing proxy.

This option should normally never be used, except in front of a proxy.

See also : ““, and “option http-server-close“.

no option http-use-htx

Switch to the new HTX internal representation for HTTP protocol elements

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

Historically, the HTTP protocol is processed as-is. Inserting, deleting, or
modifying a header field requires to rewrite the affected part in the buffer
and to move the buffer's tail accordingly. This mode is known as the legacy
HTTP mode. Since this principle has deep roots in haproxy, the HTTP/2
protocol is converted to HTTP/1.1 before being processed this way. It also
results in the inability to establish HTTP/2 connections to servers because
of the loss of HTTP/2 semantics in the HTTP/1 representation.

HTX is the name of a totally new native internal representation for the HTTP
protocol, that is agnostic to the version and aims at preserving semantics
all along the chain. It relies on a fast parsing, tokenizing and indexing of
the protocol elements so that no more memory moves are necessary and that
most elements are directly accessed. It supports using either HTTP/1 or
HTTP/2 on any side regardless of the other side's version. It also supports
upgrades from TCP to HTTP and implicit ones from HTTP/1 to HTTP/2 (matching
the HTTP/2 preface).

This option indicates that HTX needs to be used. Since the version 2.0-dev3,
the HTX is the default mode. To switch back on the legacy HTTP mode, the
option must be explicitly disabled using the "no" prefix. For prior versions,
the feature has incomplete functional coverage, so it is not enabled by
default.

See also : “mode http”

option httpchk

option httpchk

Enable HTTP protocol to check on the servers health

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<method>  is the optional HTTP method used with the requests. When not set,
          the "OPTIONS" method is used, as it generally requires low server
          processing and is easy to filter out from the logs. Any method
          may be used, though it is not recommended to invent non-standard
          ones.

<uri>     is the URI referenced in the HTTP requests. It defaults to " / "
          which is accessible by default on almost any server, but may be
          changed to any other URI. Query strings are permitted.

<version> is the optional HTTP version string. It defaults to "HTTP/1.0"
          but some servers might behave incorrectly in HTTP 1.0, so turning
          it to HTTP/1.1 may sometimes help. Note that the Host field is
          mandatory in HTTP/1.1, and as a trick, it is possible to pass it
          after "\r\n" following the version string.

By default, server health checks only consist in trying to establish a TCP
connection. When "" is specified, a complete HTTP request is
sent once the TCP connection is established, and responses 2xx and 3xx are
considered valid, while all other ones indicate a server failure, including
the lack of any response.

The port and interval are specified in the server configuration.

This option does not necessarily require an HTTP backend, it also works with
plain TCP backends. This is particularly useful to check simple scripts bound
to some dedicated ports using the inetd daemon.

Examples :

# Relay HTTPS traffic to Apache instance and check service availability
# using HTTP request "OPTIONS * HTTP/1.1" on port 80.
backend https_relay
    mode tcp
    option httpchk OPTIONS * HTTP/1.1\r\nHost:\ www
    server apache1 192.168.1.1:443 check port 80

See also : “option ssl-hello-chk“, ““, “option mysql-check“, ““, “http-check“ and the ““, “port“ and ““ server options.

option httpclose

Enable or disable HTTP connection closing

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "" or "option http-tunnel".

If "" is set, HAProxy will close connections with the server
and the client as soon as the request and the response are received. It will
also check if a "Connection: close" header is already set in each direction,
and will add one if missing. Any "Connection" header different from "close"
will also be removed.

This option may also be combined with "option http-pretend-keepalive", which
will disable sending of the "Connection: close" header, but will still cause
the connection to be closed once the whole response is received.

This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
It disables and replaces any previous "",
"option http-keep-alive" or "". Please check section 4
("Proxies") to see how this option combines with others when frontend and
backend options differ.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““ and “1.1. The HTTP transaction model”.

option httplog [ clf ]

Enable logging of HTTP request, session state and timers

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

clf       if the "clf" argument is added, then the output format will be
          the CLF format instead of HAProxy's default HTTP format. You can
          use this when you need to feed HAProxy's logs through a specific
          log analyzer which only support the CLF format and which is not
          extensible.

By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"", each log line turns into a much richer format including,
but not limited to, the HTTP request, the connection timers, the session
status, the connections numbers, the captured headers and cookies, the
frontend, backend and server name, and of course the source address and
ports.

Specifying only "option httplog" will automatically clear the 'clf' mode
if it was set by default.

"" overrides any previous "log-format" directive.

See also : about logging.

option http_proxy

Enable or disable plain HTTP proxy mode

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

It sometimes happens that people need a pure HTTP proxy which understands
basic proxy requests without caching nor any fancy feature. In this case,
it may be worth setting up an HAProxy instance with the "option http_proxy"
set. In this mode, no server is declared, and the connection is forwarded to
the IP address and port found in the URL after the "http://" scheme.

No host address resolution is performed, so this only works when pure IP
addresses are passed. Since this option's usage perimeter is rather limited,
it will probably be used only by experts who know they need exactly it. This
is incompatible with the HTTP tunnel mode.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Example :

# this backend understands HTTP proxy requests and forwards them directly.
backend direct_forward
    option httpclose
    option http_proxy

See also : ““

option independent-streams

Enable or disable independent timeout processing for both directions

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

By default, when data is sent over a socket, both the write timeout and the
read timeout for that socket are refreshed, because we consider that there is
activity on that socket, and we have no other means of guessing if we should
receive data or not.

While this default behavior is desirable for almost all applications, there
exists a situation where it is desirable to disable it, and only refresh the
read timeout if there are incoming data. This happens on sessions with large
timeouts and low amounts of exchanged data such as telnet session. If the
server suddenly disappears, the output data accumulates in the system's
socket buffers, both timeouts are correctly refreshed, and there is no way
to know the server does not receive them, so we don't timeout. However, when
the underlying protocol always echoes sent data, it would be enough by itself
to detect the issue using the read timeout. Note that this problem does not
happen with more verbose protocols because data won't accumulate long in the
socket buffers.

When this option is set on the frontend, it will disable read timeout updates
on data sent to the client. There probably is little use of this case. When
the option is set on the backend, it will disable read timeout updates on
data sent to the server. Doing so will typically break large HTTP posts from
slow lines, so use it with caution.

Note: older versions used to call this setting "option independant-streams"
      with a spelling mistake. This spelling is still supported but
      deprecated.

See also : “timeout client“, ““ and “timeout tunnel“

Use LDAPv3 health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

It is possible to test that the server correctly talks LDAPv3 instead of just
testing that it accepts the TCP connection. When this option is set, an
LDAPv3 anonymous simple bind message is sent to the server, and the response
is analyzed to find an LDAPv3 bind response message.

The server is considered valid only when the LDAP response contains success
resultCode (http://tools.ietf.org/html/rfc4511#section-4.1.9).

Logging of bind requests is server dependent see your documentation how to
configure it.

Example :

option ldap-check

See also : “option httpchk“

Use external processes for server health checks

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

It is possible to test the health of a server using an external command.
This is achieved by running the executable set using "external-check
command".

Requires the "external-check
This keyword is available in sections :
Alphabetically sorted keywords reference
" global to be set.

See also : “

• This keyword is available in sections :
• Process management and security

“, “external-check command“, ““

option log-health-checks

Enable or disable logging of health checks status updates

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

By default, failed health check are logged if server is UP and successful
health checks are logged if server is DOWN, so the amount of additional
information is limited.

When this option is enabled, any change of the health check status or to
the server's health will be logged, so that it becomes possible to know
that a server was failing occasional checks before crashing, or exactly when
it failed to respond a valid HTTP status, then when the port started to
reject connections, then when the server stopped responding at all.

Note that status changes not caused by health checks (e.g. enable/disable on
the CLI) are intentionally not logged by this option.

See also: “option httpchk“, ““, “option mysql-check“, ““, “option redis-check“, ““, “option tcp-check“, “

• This keyword is available in sections :
• Process management and security

“ and section 8 about logging.

no option log-separate-errors

Change log level for non-completely successful connections

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

Sometimes looking for errors in logs is not easy. This option makes haproxy
raise the level of logs containing potentially interesting information such
as errors, timeouts, retries, redispatches, or HTTP status codes 5xx. The
level changes from "info" to "err". This makes it possible to log them
separately to a different file with most syslog daemons. Be careful not to
remove them from the original file, otherwise you would lose ordering which
provides very important information.

Using this option, large sites dealing with several thousand connections per
second may log normal traffic to a rotating buffer and only archive smaller
error logs.

See also : “

• This keyword is available in sections :
• Process management and security

“, “dontlognull“, ““ and section 8 about logging.

no option logasap

Enable or disable early logging of HTTP requests

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

By default, HTTP requests are logged upon termination so that the total
transfer time and the number of bytes appear in the logs. When large objects
are being transferred, it may take a while before the request appears in the
logs. Using "", the request gets logged as soon as the server
sends the complete headers. The only missing information in the logs will be
the total number of bytes which will indicate everything except the amount
of data transferred, and the total time which will not take the transfer
time into account. In such a situation, it's a good practice to capture the
"Content-Length" response header so that the logs at least indicate how many
bytes are expected to be transferred.

Examples :

  listen http_proxy 0.0.0.0:80
      mode http
      option httplog
      option logasap
      log 192.168.2.200 local3

>>> Feb  6 12:14:14 localhost \
      haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in \
      static/srv1 9/10/7/14/+30 200 +243 - - ---- 3/1/1/1/0 1/0 \
      "GET /image.iso HTTP/1.0"

See also : “option httplog“, ““, and section 8 about logging.

[ user [ post-41 ] ]

Use MySQL health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<username> This is the username which will be used when connecting to MySQL
           server.
post-41    Send post v4.1 client compatible checks

If you specify a username, the check consists of sending two MySQL packet,
one Client Authentication packet, and one QUIT packet, to correctly close
MySQL session. We then parse the MySQL Handshake Initialization packet and/or
Error packet. It is a basic but useful test which does not produce error nor
aborted connect on the server. However, it requires adding an authorization
in the MySQL table, like this :

    USE mysql;
    INSERT INTO user (Host,User) values ('<ip_of_haproxy>','<username>');
    FLUSH PRIVILEGES;

If you don't specify a username (it is deprecated and not recommended), the
check only consists in parsing the Mysql Handshake Initialization packet or
Error packet, we don't send anything in this mode. It was reported that it
can generate lockout if check is too frequent and/or if there is not enough
traffic. In fact, you need in this case to check MySQL "max_connect_errors"
value as if a connection is established successfully within fewer than MySQL
"max_connect_errors" attempts after a previous connection was interrupted,
the error count for the host is cleared to zero. If HAProxy's server get
blocked, the "FLUSH HOSTS" statement is the only way to unblock it.

Remember that this does not check database presence nor database consistency.
To do this, you can use an external check with xinetd for example.

The check requires MySQL >=3.22, for older version, please use TCP check.

Most often, an incoming MySQL server needs to see the client's IP address for
various purposes, including IP privilege matching and connection logging.
When possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source
This keyword is available in sections :
Server and default-server options
" keyword,
which requires the transparent proxy feature to be compiled in, and the MySQL
server to route the client via the machine hosting haproxy.

See also: ““

option nolinger

Enable or disable immediate session resource cleaning after close

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

When clients or servers abort connections in a dirty way (e.g. they are
physically disconnected), the session timeouts triggers and the session is
closed. But it will remain in FIN_WAIT1 state for some time in the system,
using some resources and possibly limiting the ability to establish newer
connections.

When this happens, it is possible to activate "option nolinger" which forces
the system to immediately remove any socket's pending data on close. Thus,
the session is instantly purged from the system's tables. This usually has
side effects such as increased number of TCP resets due to old retransmits
getting immediately rejected. Some firewalls may sometimes complain about
this too.

For this reason, it is not recommended to use this option when not absolutely
needed. You know that you need it when you have thousands of FIN_WAIT1
sessions on your system (TIME_WAIT ones do not count).

This option may be used both on frontends and backends, depending on the side
where it is required. Use it on the frontend for clients, and on the backend
for servers.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

[ except ] [ header ]

Enable insertion of the X-Original-To header to requests sent to servers

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<network> is an optional argument used to disable this option for sources
          matching <network>
<name>    an optional argument to specify a different "X-Original-To"
          header name.

Since HAProxy can work in transparent mode, every request from a client can
be redirected to the proxy and HAProxy itself can proxy every request to a
complex SQUID environment and the destination host from SO_ORIGINAL_DST will
be lost. This is annoying when you want access rules based on destination ip
addresses. To solve this problem, a new HTTP header "X-Original-To" may be
added by HAProxy to all requests sent to the server. This header contains a
value representing the original destination IP address. Since this must be
configured to always use the last occurrence of this header only. Note that
only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.

The keyword "header" may be used to supply a different header name to replace
the default "X-Original-To". This can be useful where you might already
have a "X-Original-To" header from a different application, and you need
preserve it. Also if your backend server doesn't use the "X-Original-To"
header and requires different one.

Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.

This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined.

Examples :

# Original Destination address
frontend www
    mode http
    option originalto except 127.0.0.1

# Those servers want the IP Address in X-Client-Dst
backend www
    mode http
    option originalto header X-Client-Dst

See also : “option httpclose“, ““.

option persist

Enable or disable forced persistence on down servers

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When an HTTP request reaches a backend with a cookie which references a dead
server, by default it is redispatched to another server. It is possible to
force the request to be sent to the dead server first using "option persist"
if absolutely needed. A common use case is when servers are under extreme
load and spend their time flapping. In this case, the users would still be
directed to the server they opened the session on, in the hope they would be
correctly served. It is recommended to use "" in conjunction
with this option so that in the event it would not be possible to connect to
the server at all (server definitely dead), the client would finally be
redirected to another valid server.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option redispatch“, ““, “force-persist“

[ user ]

Use PostgreSQL health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<username> This is the username which will be used when connecting to
           PostgreSQL server.

The check sends a PostgreSQL StartupMessage and waits for either
Authentication request or ErrorResponse message. It is a basic but useful
test which does not produce error nor aborted connect on the server.
This check is identical with the "mysql-check".

See also: ““

option prefer-last-server

Allow multiple load balanced requests to remain on the same server

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When the load balancing algorithm in use is not deterministic, and a previous
request was sent to a server to which haproxy still holds a connection, it is
sometimes desirable that subsequent requests on a same session go to the same
server as much as possible. Note that this is different from persistence, as
we only indicate a preference which haproxy tries to apply without any form
of warranty. The real use is for keep-alive connections sent to servers. When
this option is used, haproxy will try to reuse the same connection that is
attached to the server instead of rebalancing to another server, causing a
close of the connection. This can make sense for static file servers. It does
not make much sense to use this in combination with hashing algorithms. Note,
haproxy already automatically tries to stick to a server which sends a 401 or
to a proxy which sends a 407 (authentication required), when the load
balancing algorithm is not deterministic. This is mandatory for use with the
broken NTLM authentication challenge, and significantly helps in
troubleshooting some faulty applications. Option prefer-last-server might be
desirable in these environments as well, to avoid redistributing the traffic
after every other response.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also: “option http-keep-alive“

option redispatch

Enable or disable session redistribution in case of connection failure

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<interval> The optional integer value that controls how often redispatches
           occur when retrying connections. Positive value P indicates a
           redispatch is desired on every Pth retry, and negative value
           N indicate a redispatch is desired on the Nth retry prior to the
           last retry. For example, the default of -1 preserves the
           historical behavior of redispatching on the last retry, a
           positive value of 1 would indicate a redispatch on every retry,
           and a positive value of 3 would indicate a redispatch on every
           third retry. You can disable redispatches with a value of 0.

In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.

Specifying "option redispatch" will allow the proxy to break cookie or
consistent hash based persistence and redistribute them to a working server.

It also allows to retry connections to another server in case of multiple
connection failures. Of course, it requires having "" set to a nonzero
value.

This form is the preferred form, which replaces both the "redispatch" and
"" keywords.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “redispatch“, ““, “force-persist“

Use redis health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

It is possible to test that the server correctly talks REDIS protocol instead
of just testing that it accepts the TCP connection. When this option is set,
a PING redis command is sent to the server, and the response is analyzed to
find the "+PONG" response message.

Example :

option redis-check

See also : “option httpchk“, ““, “tcp-check expect“

option smtpchk

Use SMTP health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<hello>   is an optional argument. It is the "hello" command to use. It can
          be either "HELO" (for SMTP) or "EHLO" (for ESMTP). All other
          values will be turned into the default command ("HELO").

<domain>  is the domain name to present to the server. It may only be
          specified (and is mandatory) if the hello command has been
          specified. By default, "localhost" is used.

When "" is set, the health checks will consist in TCP
connections followed by an SMTP command. By default, this command is
"HELO localhost". The server's return code is analyzed and only return codes
starting with a "2" will be considered as valid. All other responses,
including a lack of response will constitute an error and will indicate a
dead server.

This test is meant to be used with SMTP servers or relays. Depending on the
request, it is possible that some servers do not log each connection attempt,
so you may want to experiment to improve the behavior. Using telnet on port
25 is often easier than adjusting the configuration.

Most often, an incoming SMTP server needs to see the client's IP address for
various purposes, including spam filtering, anti-spoofing and logging. When
possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source
This keyword is available in sections :
Server and default-server options
" keyword,
which requires the transparent proxy feature to be compiled in.

Example :

option smtpchk HELO mydomain.org

See also : ““, “source

• This keyword is available in sections :
• Server and default-server options

“

no option socket-stats

Enable or disable collecting & providing separate statistics for each socket.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

no option splice-auto

Enable or disable automatic kernel acceleration on sockets in both directions

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

When this option is enabled either on a frontend or on a backend, haproxy
will automatically evaluate the opportunity to use kernel tcp splicing to
forward data between the client and the server, in either direction. HAProxy
uses heuristics to estimate if kernel splicing might improve performance or
not. Both directions are handled independently. Note that the heuristics used
are not much aggressive in order to limit excessive use of splicing. This
option requires splicing to be enabled at compile time, and may be globally
disabled with the global option "". Since splice uses pipes, using it
requires that there are enough spare pipes.

Important note: kernel-based TCP splicing is a Linux-specific feature which
first appeared in kernel 2.6.25. It offers kernel-based acceleration to
transfer data between sockets without copying these data to user-space, thus
providing noticeable performance gains and CPU cycles savings. Since many
early implementations are buggy, corrupt data and/or are inefficient, this
feature is not enabled by default, and it should be used with extreme care.
While it is not possible to detect the correctness of an implementation,
2.6.29 is the first version offering a properly working implementation. In
case of doubt, splicing may be globally disabled using the global "nosplice"
keyword.

Example :

option splice-auto

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““, “option splice-response“, and global options ““ and “maxpipes“

no option splice-request

Enable or disable automatic kernel acceleration on sockets for requests

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

When this option is enabled either on a frontend or on a backend, haproxy
will use kernel tcp splicing whenever possible to forward data going from
the client to the server. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "".
Since splice uses pipes, using it requires that there are enough spare pipes.

Important note: see "option splice-auto" for usage limitations.

Example :

option splice-request

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““, “option splice-response“, and global options ““ and “maxpipes“

no option splice-response

Enable or disable automatic kernel acceleration on sockets for responses

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

When this option is enabled either on a frontend or on a backend, haproxy
will use kernel tcp splicing whenever possible to forward data going from
the server to the client. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "".
Since splice uses pipes, using it requires that there are enough spare pipes.

Important note: see "option splice-auto" for usage limitations.

Example :

option splice-response

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : ““, “option splice-request“, and global options ““ and “maxpipes“

Use SPOP health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
no	no	no	yes

Arguments : none

It is possible to test that the server correctly talks SPOP protocol instead
of just testing that it accepts the TCP connection. When this option is set,
a HELLO handshake is performed between HAProxy and the server, and the
response is analyzed to check no error is reported.

Example :

option spop-check

See also : “option httpchk“

no option srvtcpka

Enable or disable the sending of TCP keepalive packets on the server side

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "" enables the emission of TCP keep-alive probes on the
server side of a connection, which should help when session expirations are
noticed between HAProxy and a server.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option clitcpka“, ““

option ssl-hello-chk

Use SSLv3 client hello health checks for server testing

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

When some SSL-based protocols are relayed in TCP mode through HAProxy, it is
possible to test that the server correctly talks SSL instead of just testing
that it accepts the TCP connection. When "" is set, pure
SSLv3 client hello messages are sent once the connection is established to
the server, and the response is analyzed to find an SSL server hello message.
The server is considered valid only when the response contains this server
hello message.

All servers tested till there correctly reply to SSLv3 client hello messages,
and most servers tested do not even log the requests containing only hello
messages, which is appreciable.

Note that this check works even when SSL support was not built into haproxy
because it forges the SSL message. When SSL support is available, it is best
to use native SSL health checks instead of this one.

See also: “option httpchk“, ““

option tcp-check

Perform health checks using tcp-check send/expect sequences

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

This health check method is intended to be combined with "" command
lists in order to support send/expect types of health check sequences.

TCP checks currently support 4 modes of operations :
  - no "tcp-check" directive : the health check only consists in a connection
    attempt, which remains the default mode.

  - "" or "tcp-check send-binary" only is mentioned : this is
    used to send a string along with a connection opening. With some
    protocols, it helps sending a "QUIT" message for example that prevents
    the server from logging a connection error for each health check. The
    check result will still be based on the ability to open the connection
    only.

  - "" only is mentioned : this is used to test a banner.
    The connection is opened and haproxy waits for the server to present some
    contents which must validate some rules. The check result will be based
    on the matching between the contents and the rules. This is suited for
    POP, IMAP, SMTP, FTP, SSH, TELNET.

  - both "tcp-check send" and "" are mentioned : this is
    used to test a hello-type protocol. HAProxy sends a message, the server
    responds and its response is analyzed. the check result will be based on
    the matching between the response contents and the rules. This is often
    suited for protocols which require a binding or a request/response model.
    LDAP, MySQL, Redis and SSL are example of such protocols, though they
    already all have their dedicated checks with a deeper understanding of
    the respective protocols.
    In this mode, many questions may be sent and many answers may be
    analyzed.

  A fifth mode can be used to insert comments in different steps of the
  script.

  For each tcp-check rule you create, you can add a "comment" directive,
  followed by a string. This string will be reported in the log and stderr
  in debug mode. It is useful to make user-friendly error reporting.
  The "comment" is of course optional.

Examples :

# perform a POP check (analyze only server's banner)
option tcp-check
tcp-check expect string +OK\ POP3\ ready comment POP\ protocol

# perform an IMAP check (analyze only server's banner)
option tcp-check
tcp-check expect string *\ OK\ IMAP4\ ready comment IMAP\ protocol

# look for the redis master server after ensuring it speaks well
# redis protocol, then it exits properly.
# (send a command then analyze the response 3 times)
option tcp-check
tcp-check comment PING\ phase
tcp-check send PING\r\n
tcp-check expect string +PONG
tcp-check comment role\ check
tcp-check send info\ replication\r\n
tcp-check expect string role:master
tcp-check comment QUIT\ phase
tcp-check send QUIT\r\n
tcp-check expect string +OK

forge a HTTP request, then analyze the response
(send many headers before analyzing)
option tcp-check
tcp-check comment forge\ and\ send\ HTTP\ request
tcp-check send HEAD\ /\ HTTP/1.1\r\n
tcp-check send Host:\ www.mydomain.com\r\n
tcp-check send User-Agent:\ HAProxy\ tcpcheck\r\n
tcp-check send \r\n
tcp-check expect rstring HTTP/1\..\ (2..|3..) comment check\ HTTP\ response

See also : “tcp-check expect“, ““

option tcp-smart-accept

Enable or disable the saving of one ACK packet during the accept sequence

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

When an HTTP connection request comes in, the system acknowledges it on
behalf of HAProxy, then the client immediately sends its request, and the
system acknowledges it too while it is notifying HAProxy about the new
connection. HAProxy then reads the request and responds. This means that we
have one TCP ACK sent by the system for nothing, because the request could
very well be acknowledged by HAProxy when it sends its response.

For this reason, in HTTP mode, HAProxy automatically asks the system to avoid
sending this useless ACK on platforms which support it (currently at least
Linux). It must not cause any problem, because the system will send it anyway
after 40 ms if the response takes more time than expected to come.

During complex network debugging sessions, it may be desirable to disable
this optimization because delayed ACKs can make troubleshooting more complex
when trying to identify where packets are delayed. It is then possible to
fall back to normal behavior by specifying "no option tcp-smart-accept".

It is also possible to force it for non-HTTP proxies by simply specifying
"". For instance, it can make sense with some services
such as SMTP where the server speaks first.

It is recommended to avoid forcing this option in a defaults section. In case
of doubt, consider setting it back to automatic values by prepending the
"default" keyword before it, or disabling it using the "no" keyword.

See also : “option tcp-smart-connect“

no option tcp-smart-connect

Enable or disable the saving of one ACK packet during the connect sequence

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

On certain systems (at least Linux), HAProxy can ask the kernel not to
immediately send an empty ACK upon a connection request, but to directly
send the buffer request instead. This saves one packet on the network and
thus boosts performance. It can also be useful for some servers, because they
immediately get the request along with the incoming connection.

This feature is enabled when "" is set in a backend.
It is not enabled by default because it makes network troubleshooting more
complex.

It only makes sense to enable it with protocols where the client speaks first
such as HTTP. In other situations, if there is no data to send in place of
the ACK, a normal ACK is sent.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

See also : “option tcp-smart-accept“

Enable or disable the sending of TCP keepalive packets on both sides

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "tcpka" enables the emission of TCP keep-alive probes on both
the client and server sides of a connection. Note that this is meaningful
only in "defaults" or "listen" sections. If this option is used in a
frontend, only the client side will get keep-alives, and if this option is
used in a backend, only the server side will get keep-alives. For this
reason, it is strongly recommended to explicitly use "" and
"option srvtcpka" when the configuration is split between frontends and
backends.

See also : ““, “option srvtcpka“

Enable advanced logging of TCP connections with session state and timers

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments : none

By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"option tcplog", each log line turns into a much richer format including, but
not limited to, the connection timers, the session status, the connections
numbers, the frontend, backend and server name, and of course the source
address and ports. This option is useful for pure TCP proxies in order to
find which of the client or server disconnects or times out. For normal HTTP
proxies, it's better to use "" which is even more complete.

"option tcplog" overrides any previous "" directive.

See also : “option httplog“, and about logging.

option transparent

Enable client-side transparent proxying

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

This option was introduced in order to provide layer 7 persistence to layer 3
load balancers. The idea is to use the OS's ability to redirect an incoming
connection for a remote address to a local process (here HAProxy), and let
this process know what address was initially requested. When this option is
used, sessions without cookies will be forwarded to the original destination
IP address of the incoming request (which should match that of another
equipment), while requests with cookies will still be forwarded to the
appropriate server.

Note that contrary to a common belief, this option does NOT make HAProxy
present the client's IP to the server when establishing the connection.

See also: the “usesrc” argument of the “source

• This keyword is available in sections :
• Server and default-server options

“ keyword, and the ““ option of the “bind

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“ keyword.

Executable to run when performing an external-check

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<command> is the external command to run

The arguments passed to the to the command are:

<proxy_address> <proxy_port> <server_address> <server_port>

The <proxy_address> and <proxy_port> are derived from the first listener
that is either IPv4, IPv6 or a UNIX socket. In the case of a UNIX socket
listener the proxy_address will be the path of the socket and the
<proxy_port> will be the string "NOT_USED". In a backend section, it's not
possible to determine a listener, and both <proxy_address> and <proxy_port>
will have the string value "NOT_USED".

Some values are also provided through environment variables.

Environment variables :
  HAPROXY_PROXY_ADDR      The first bind address if available (or empty if not
                          applicable, for example in a "backend" section).

  HAPROXY_PROXY_ID        The backend id.

  HAPROXY_PROXY_NAME      The backend name.

  HAPROXY_PROXY_PORT      The first bind port if available (or empty if not
                          applicable, for example in a "backend" section or
                          for a UNIX socket).

  HAPROXY_SERVER_ADDR     The server address.

  HAPROXY_SERVER_CURCONN  The current number of connections on the server.

  HAPROXY_SERVER_ID       The server id.

  HAPROXY_SERVER_MAXCONN  The server max connections.

  HAPROXY_SERVER_NAME     The server name.

  HAPROXY_SERVER_PORT     The server port if available (or empty for a UNIX
                          socket).

  PATH                    The PATH environment variable used when executing
                          the command may be set using "external-check path".

See also "2.3. Environment variables" for other variables.

If the command executed and exits with a zero status then the check is
considered to have passed, otherwise the check is considered to have
failed.

Example :

external-check command /bin/true

See also : “

• This keyword is available in sections :
• Process management and security

“, “option external-check“, ““

external-check path

The value of the PATH environment variable used when running an external-check

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<path> is the path used when executing external command to run

The default path is "".

Example :

external-check path "/usr/bin:/bin"

See also : “

• This keyword is available in sections :
• Process management and security

“, “option external-check“, ““

persist rdp-cookie

()

Enable RDP cookie-based persistence

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<name>    is the optional name of the RDP cookie to check. If omitted, the
          default cookie name "msts" will be used. There currently is no
          valid reason to change this name.

This statement enables persistence based on an RDP cookie. The RDP cookie
contains all information required to find the server in the list of known
servers. So when this option is set in the backend, the request is analyzed
and if an RDP cookie is found, it is decoded. If it matches a known server
which is still UP (or if "option persist" is set), then the connection is
forwarded to this server.

Note that this only makes sense in a TCP backend, but for this to work, the
frontend must have waited long enough to ensure that an RDP cookie is present
in the request buffer. This is the same requirement as with the "rdp-cookie"
load-balancing method. Thus it is highly recommended to put all statements in
a single "listen" section.

Also, it is important to understand that the terminal server will emit this
RDP cookie only if it is configured for "token redirection mode", which means
that the "IP address redirection" option is disabled.

Example :

listen tse-farm
    bind :3389
    # wait up to 5s for an RDP cookie in the request
    tcp-request inspect-delay 5s
    tcp-request content accept if RDP_COOKIE
    # apply RDP cookie persistence
    persist rdp-cookie
    # if server is unknown, let's balance on the same cookie.
    # alternatively, "balance leastconn" may be useful too.
    balance rdp-cookie
    server srv1 1.1.1.1:3389
    server srv2 1.1.1.2:3389

See also : “balance rdp-cookie”, ““, the “req_rdp_cookie” ACL and the rdp_cookie pattern fetch function.

rate-limit sessions

Set a limit on the number of new sessions accepted per second on a frontend

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<rate>    The <rate> parameter is an integer designating the maximum number
          of new sessions per second to accept on the frontend.

When the frontend reaches the specified number of new sessions per second, it
stops accepting new connections until the rate drops below the limit again.
During this time, the pending sessions will be kept in the socket's backlog
(in system buffers) and haproxy will not even be aware that sessions are
pending. When applying very low limit on a highly loaded service, it may make
sense to increase the socket's backlog using the "
This keyword is available in sections :
Alphabetically sorted keywords reference
" keyword.

This feature is particularly efficient at blocking connection-based attacks
or service abuse on fragile servers. Since the session rate is measured every
millisecond, it is extremely accurate. Also, the limit applies immediately,
no delay is needed at all to detect the threshold.

Example :

Limit the connection rate on SMTP to 10 per second max
listen smtp
    mode tcp
    bind :25
    rate-limit sessions 10
    server smtp1 127.0.0.1:1025

Note : when the maximum rate is reached, the frontend's status is not changed
       but its sockets appear as "WAITING" in the statistics if the
       "socket-stats" option is enabled.

See also : the “

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“ keyword and the “fe_sess_rate“ ACL criterion.

[code ] [{if | unless} ]

redirect prefix [code ] [{if | unless} ]

[code ] [{if | unless} ]

Return an HTTP redirection if/unless a condition is matched

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

If/unless the condition is matched, the HTTP request will lead to a redirect
response. If no condition is specified, the redirect applies unconditionally.

Arguments :

<loc>     With "redirect location", the exact value in <loc> is placed into
          the HTTP "Location" header. When used in an "
This keyword is available in sections :
Proxy section
" rule,
          <loc> value follows the log-format rules and can include some
          dynamic values (see Custom Log Format in section 8.2.4).

<pfx>     With "", the "Location" header is built from the
          concatenation of <pfx> and the complete URI path, including the
          query string, unless the "drop-query" option is specified (see
          below). As a special case, if <pfx> equals exactly "/", then
          nothing is inserted before the original URI. It allows one to
          redirect to the same URL (for instance, to insert a cookie). When
          used in an "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
" rule, <pfx> value follows the log-format
          rules and can include some dynamic values (see Custom Log Format
          in ).

<sch>     With "redirect scheme", then the "Location" header is built by
          concatenating <sch> with "://" then the first occurrence of the
          "Host" header, and then the URI path, including the query string
          unless the "drop-query" option is specified (see below). If no
          path is found or if the path is "*", then "/" is used instead. If
          no "Host" header is found, then an empty host component will be
          returned, which most recent browsers interpret as redirecting to
          the same host. This directive is mostly used to redirect HTTP to
          HTTPS. When used in an "
This keyword is available in sections :
Proxy section
" rule, <sch> value follows
          the log-format rules and can include some dynamic values (see
          Custom Log Format in section 8.2.4).

<code>    The code is optional. It indicates which type of HTTP redirection
          is desired. Only codes 301, 302, 303, 307 and 308 are supported,
          with 302 used by default if no code is specified. 301 means
          "Moved permanently", and a browser may cache the Location. 302
          means "Moved temporarily" and means that the browser should not
          cache the redirection. 303 is equivalent to 302 except that the
          browser will fetch the location with a GET method. 307 is just
          like 302 but makes it clear that the same method must be reused.
          Likewise, 308 replaces 301 if the same method must be used.

<option>  There are several options which can be specified to adjust the
          expected behavior of a redirection :

  - "drop-query"
    When this keyword is used in a prefix-based redirection, then the
    location will be set without any possible query-string, which is useful
    for directing users to a non-secure page for instance. It has no effect
    with a location-type redirect.

  - "append-slash"
    This keyword may be used in conjunction with "drop-query" to redirect
    users who use a URL not ending with a '/' to the same one with the '/'.
    It can be useful to ensure that search engines will only see one URL.
    For this, a return code 301 is preferred.

  - "set-cookie NAME[=value]"
    A "Set-Cookie" header will be added with NAME (and optionally "=value")
    to the response. This is sometimes used to indicate that a user has
    been seen, for instance to protect against some types of DoS. No other
    cookie option is added, so the cookie will be a session cookie. Note
    that for a browser, a sole cookie name without an equal sign is
    different from a cookie with an equal sign.

  - "clear-cookie NAME[=]"
    A "Set-Cookie" header will be added with NAME (and optionally "="), but
    with the "Max-Age" attribute set to zero. This will tell the browser to
    delete this cookie. It is useful for instance on logout pages. It is
    important to note that clearing the cookie "NAME" will not remove a
    cookie set with "NAME=value". You have to clear the cookie "NAME=" for
    that, because the browser makes the difference.

Example:

Move the login URL only to HTTPS.
acl clear      dst_port  80
acl secure     dst_port  8080
acl login_page url_beg   /login
acl logout     url_beg   /logout
acl uid_given  url_reg   /login?userid=[^&]+
acl cookie_set hdr_sub(cookie) SEEN=1

redirect prefix   https://mysite.com set-cookie SEEN=1 if !cookie_set
redirect prefix   https://mysite.com           if login_page !secure
redirect prefix   http://mysite.com drop-query if login_page !uid_given
redirect location http://mysite.com/           if !login_page secure
redirect location / clear-cookie USERID=       if logout

Example:

Send redirects for request for articles without a '/'.
acl missing_slash path_reg ^/article/[^/]*$
redirect code 301 prefix / drop-query append-slash if missing_slash

Example:

Redirect all HTTP traffic to HTTPS when SSL is handled by haproxy.
redirect scheme https if !{ ssl_fc }

Example:

Append 'www.' prefix in front of all hosts not having it
http-request redirect code 301 location      \
  http://www.%[hdr(host)]%[capture.req.uri]  \
  unless { hdr_beg(host) -i www }

See  about ACL usage.

redispatch (deprecated)

Enable or disable session redistribution in case of connection failure

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.

Specifying "" will allow the proxy to break their persistence and
redistribute them to a working server.

It also allows to retry last connection to another server in case of multiple
connection failures. Of course, it requires having "retries" set to a nonzero
value.

This form is deprecated, do not use it in any new configuration, use the new
"" instead.

See also : “option redispatch“

[{if | unless} ] (deprecated)

Add a header at the end of the HTTP request

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP request.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.

Example :

Add "X-Proto: SSL" to requests coming via port 81
acl is-ssl  dst_port       81
reqadd      X-Proto:\ SSL  if is-ssl

See also: “rspadd“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

reqallow [{if | unless} ] (deprecated)

[{if | unless} ] (ignore case) (deprecated)

Definitely allow an HTTP request if a line matches a regular expression

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqallow" keyword strictly matches case while ""
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will mark the request as allowed, even if any later test would
result in a deny. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

Example :

# allow www.* but refuse *.local
reqiallow ^Host:\ www\.
reqideny  ^Host:\ .*\.local

See also: “reqdeny“, ““, “http-request

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, about HTTP header manipulation, and section 7 about ACLs.

[{if | unless} ] (deprecated)

reqidel [{if | unless} ] (ignore case) (deprecated)

May be used in sections :

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The ""
          keyword strictly matches case while "reqidel" ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any header line matching extended regular expression <search> in the request
will be completely deleted. Most common use of this is to remove unwanted
and/or dangerous headers or cookies from a request before passing it to the
next servers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.

Example :

# remove X-Forwarded-For header and SERVER cookie
reqidel ^X-Forwarded-For:.*
reqidel ^Cookie:.*SERVER=

See also: ““, “reqrep“, ““, “http-request

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, about HTTP header manipulation, and section 7 about ACLs.

[{if | unless} ] (deprecated)

reqideny [{if | unless} ] (ignore case) (deprecated)

Deny an HTTP request if a line matches a regular expression

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "" keyword strictly matches case while "reqideny" ignores
          case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will mark the request as denied, even if any later test would
result in an allow. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.

A denied request will generate an "HTTP 403 forbidden" response once the
complete request has been parsed. This is consistent with what is practiced
using ACLs.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

Example :

# refuse *.local, then allow www.*
reqideny  ^Host:\ .*\.local
reqiallow ^Host:\ www\.

See also: ““, “rspdeny“, ““, “http-request

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, about HTTP header manipulation, and section 7 about ACLs.

[{if | unless} ] (deprecated)

reqipass [{if | unless} ] (ignore case) (deprecated)

Ignore any HTTP request line matching a regular expression in next rules

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "" keyword strictly matches case while "reqipass" ignores
          case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will skip next rules, without assigning any deny or allow verdict.
The test applies both to the request line and to request headers. Keep in
mind that URLs in request line are case-sensitive while header names are not.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

Example :

# refuse *.local, then allow www.*, but ignore "www.private.local"
reqipass  ^Host:\ www.private\.local
reqideny  ^Host:\ .*\.local
reqiallow ^Host:\ www\.

See also: ““, “reqdeny“, ““, “http-request

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“, about HTTP header manipulation, and section 7 about ACLs.

[{if | unless} ] (deprecated)

reqirep [{if | unless} ] (ignore case) (deprecated)

Replace a regular expression with a string in an HTTP request line

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The ""
          keyword strictly matches case while "reqirep" ignores case.

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). References to matched
          pattern groups are possible using the common \N form, with N
          being a single digit between 0 and 9. Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any line matching extended regular expression <search> in the request (both
the request line and header lines) will be completely replaced with <string>.
Most common use of this is to rewrite URLs or domain names in "Host" headers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that URLs in
request line are case-sensitive while header names are not.

Example :

# replace "/static/" with "/" at the beginning of any request path.
reqrep ^([^\ :]*)\ /static/(.*)     \1\ /\2
# replace "www.mydomain.com" with "www" in the host name.
reqirep ^Host:\ www.mydomain.com   Host:\ www

See also: ““, “reqdel“, ““, “tune.bufsize“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

reqtarpit [{if | unless} ] (deprecated)

[{if | unless} ] (ignore case) (deprecated)

Tarpit an HTTP request containing a line matching a regular expression

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqtarpit" keyword strictly matches case while ""
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will be tarpitted, which means that it will connect to nowhere, will
be kept open for a pre-defined time, then will return an HTTP error 500 so
that the attacker does not suspect it has been tarpitted. The status 500 will
be reported in the logs, but the completion flags will indicate "PT". The
delay is defined by "timeout tarpit", or "" if the former is
not set.

The goal of the tarpit is to slow down robots attacking servers with
identifiable requests. Many robots limit their outgoing number of connections
and stay connected waiting for a reply which can take several minutes to
come. Depending on the environment and attack, it may be particularly
efficient at reducing the load on the network and firewalls.

Examples :

# ignore user-agents reporting any flavor of "Mozilla" or "MSIE", but
# block all others.
reqipass   ^User-Agent:\.*(Mozilla|MSIE)
reqitarpit ^User-Agent:

# block bad guys
acl badguys src 10.1.0.3 172.16.13.20/28
reqitarpit . if badguys

See also: “reqallow“, ““, “reqpass“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

retries

Set the number of retries to perform on a server after a connection failure

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<value>   is the number of times a connection attempt should be retried on
          a server when a connection either is refused or times out. The
          default value is 3.

It is important to understand that this value applies to the number of
connection attempts, not full requests. When a connection has effectively
been established to a server, there will be no more retry.

In order to avoid immediate reconnections to a server which is restarting,
a turn-around timer of min("", one second) is applied before
a retry occurs.

When "option redispatch" is set, the last retry may be performed on another
server even if a cookie references a different server.

See also : ““

retry-on [list of keywords]

Specify when to attempt to automatically retry a failed request

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<keywords>  is a list of keywords or HTTP status codes, each representing a
            type of failure event on which an attempt to retry the request
            is desired. Please read the notes at the bottom before changing
            this setting. The following keywords are supported :

  none              never retry

  conn-failure      retry when the connection or the SSL handshake failed
                    and the request could not be sent. This is the default.

  empty-response    retry when the server connection was closed after part
                    of the request was sent, and nothing was received from
                    the server. This type of failure may be caused by the
                    request timeout on the server side, poor network
                    condition, or a server crash or restart while
                    processing the request.

  junk-response     retry when the server returned something not looking
                    like a complete HTTP response. This includes partial
                    responses headers as well as non-HTTP contents. It
                    usually is a bad idea to retry on such events, which
                    may be caused a configuration issue (wrong server port)
                    or by the request being harmful to the server (buffer
                    overflow attack for example).

  response-timeout  the server timeout stroke while waiting for the server
                    to respond to the request. This may be caused by poor
                    network condition, the reuse of an idle connection
                    which has expired on the path, or by the request being
                    extremely expensive to process. It generally is a bad
                    idea to retry on such events on servers dealing with
                    heavy database processing (full scans, etc) as it may
                    amplify denial of service attacks.

  0rtt-rejected     retry requests which were sent over early data and were
                    rejected by the server. These requests are generally
                    considered to be safe to retry.

  <status>          any HTTP status code among "404" (Not Found), "408"
                    (Request Timeout), "425" (Too Early), "500" (Server
                    Error), "501" (Not Implemented), "502" (Bad Gateway),
                    "503" (Service Unavailable), "504" (Gateway Timeout).

  all-retryable-errors
                    retry request for any error that are considered
                    retryable. This currently activates "conn-failure",
                    "empty-response", "junk-response", "response-timeout",
                    "0rtt-rejected", "500", "502", "503", and "504".

Using this directive replaces any previous settings with the new ones; it is
not cumulative.

Please note that using anything other than "none" and "conn-failure" requires
to allocate a buffer and copy the whole request into it, so it has memory and
performance impacts. Requests not fitting in a single buffer will never be
retried (see the global tune.bufsize setting).

You have to make sure the application has a replay protection mechanism built
in such as a unique transaction IDs passed in requests, or that replaying the
same request has no consequence, or it is very dangerous to use any retry-on
value beside "conn-failure" and "none". Static file servers and caches are
generally considered safe against any type of retry. Using a status code can
be useful to quickly leave a server showing an abnormal behavior (out of
memory, file system issues, etc), but in this case it may be a good idea to
immediately redispatch the connection to another server (please see "option
redispatch" for this). Last, it is important to understand that most causes
of failures are the requests themselves and that retrying a request causing a
server to misbehave will often make the situation even worse for this server,
or for the whole service in case of redispatch.

Unless you know exactly how the application deals with replayed requests, you
should not use this directive.

The default is "conn-failure".

See also: ““, “option redispatch“, ““

rspadd [{if | unless} ] (deprecated)

Add a header at the end of the HTTP response

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP response.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.

See also: ““ “reqadd“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

rspdel [{if | unless} ] (deprecated)

[{if | unless} ] (ignore case) (deprecated)

Delete all headers matching a regular expression in an HTTP response

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rspdel" keyword strictly matches case while ""
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any header line matching extended regular expression <search> in the response
will be completely deleted. Most common use of this is to remove unwanted
and/or sensitive headers or cookies from a response before passing it to the
client.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.

Example :

# remove the Server header from responses
rspidel ^Server:.*

See also: “rspadd“, ““, “reqdel“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

rspdeny [{if | unless} ] (deprecated)

[{if | unless} ] (ignore case) (deprecated)

Block an HTTP response if a line matches a regular expression

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rspdeny" keyword strictly matches case while ""
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A response containing any line which matches extended regular expression
<search> will mark the request as denied. The test applies both to the
response line and to response headers. Keep in mind that header names are not
case-sensitive.

Main use of this keyword is to prevent sensitive information leak and to
block the response before it reaches the client. If a response is denied, it
will be replaced with an HTTP 502 error so that the client never retrieves
any sensitive data.

It is easier, faster and more powerful to use ACLs to write access policies.
Rspdeny should be avoided in new designs.

Example :

# Ensure that no content type matching ms-word will leak
rspideny  ^Content-type:\.*/ms-word

See also: “reqdeny“, ““, “block“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation and about ACLs.

rsprep [{if | unless} ] (deprecated)

[{if | unless} ] (ignore case) (deprecated)

Replace a regular expression with a string in an HTTP response line

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rsprep" keyword strictly matches case while ""
          ignores case.

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). References to matched
          pattern groups are possible using the common \N form, with N
          being a single digit between 0 and 9. Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any line matching extended regular expression <search> in the response (both
the response line and header lines) will be completely replaced with
<string>. Most common use of this is to rewrite Location headers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that header names
are not case-sensitive.

Example :

# replace "Location: 127.0.0.1:8080" with "Location: www.mydomain.com"
rspirep ^Location:\ 127.0.0.1:8080    Location:\ www.mydomain.com

See also: “rspadd“, ““, “reqrep“, “

• This keyword is available in sections :
• Proxy section

“, section 6 about HTTP header manipulation, and about ACLs.

server

[:[port]] [param*]

Declare a server in a backend

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<name>    is the internal name assigned to this server. This name will
          appear in logs and alerts. If "" is
          set, it will be added to the request header sent to the server.

<address> is the IPv4 or IPv6 address of the server. Alternatively, a
          resolvable hostname is supported, but this name will be resolved
          during start-up. Address "0.0.0.0" or "*" has a special meaning.
          It indicates that the connection will be forwarded to the same IP
          address as the one from the client connection. This is useful in
          transparent proxy architectures where the client's connection is
          intercepted and haproxy must forward to the original destination
          address. This is more or less what the "transparent" keyword does
          except that with a server it's possible to limit concurrency and
          to report statistics. Optionally, an address family prefix may be
          used before the address to force the family regardless of the
          address format, which can be useful to specify a path to a unix
          socket with no slash ('/'). Currently supported prefixes are :
                - 'ipv4@'  -> address is always IPv4
                - 'ipv6@'  -> address is always IPv6
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only)
                - 'sockpair@' -> address is the FD of a connected unix
                  socket or of a socketpair. During a connection, the
                  backend creates a pair of connected sockets, and passes
                  one of them over the FD. The bind part will use the
                  received socket as the client FD. Should be used
                  carefully.
          You may want to reference some environment variables in the
          address parameter, see  about environment
          variables. The "init-addr" setting can be used to modify the way
          IP addresses should be resolved upon startup.

<port>    is an optional port specification. If set, all connections will
          be sent to this port. If unset, the same port the client
          connected to will be used. The port may also be prefixed by a "+"
          or a "-". In this case, the server's port will be determined by
          adding this value to the client's port.

<param*>  is a list of parameters for this server. The "
This keyword is available in sections :
Peers
" keywords
          accepts an important number of options and has a complete section
          dedicated to it. Please refer to section 5 for more details.

Examples :

server first  10.1.1.1:1080 cookie first  check inter 1000
server second 10.1.1.2:1080 cookie second check inter 1000
server transp ipv4@
server backup "${SRV_BACKUP}:1080" backup
server www1_dc1 "${LAN_DC1}.101:80"
server www1_dc2 "${LAN_DC2}.101:80"

Note: regarding Linux's abstract namespace sockets, HAProxy uses the whole
      sun_path length is used for the address length. Some other programs
      such as socat use the string length only by default. Pass the option
      ",unix-tightsocklen=0" to any abstract socket definition in socat to
      make it compatible with HAProxy's.

See also: “

• This keyword is available in sections :
• Peers

“, “http-send-name-header“ and about server options

server-state-file-name []

Set the server state file to read, load and apply to servers available in
this backend. It only applies when the directive ""
is set to "local". When <file> is not provided or if this directive is not
set, then backend name is used. If <file> starts with a slash '/', then it is
considered as an absolute path. Otherwise, <file> is concatenated to the
global directive "server-state-file-base".

Example:

The minimal configuration below would make HAProxy look for the state server file '/etc/haproxy/states/bk':
global
  server-state-file-base /etc/haproxy/states

backend bk
  load-server-state-from-file

See also: “server-state-file-base”, “load-server-state-from-file“, and “show servers state”

[:] [params*]

Set a template to initialize servers with shared parameters.
The names of these servers are built from <prefix> and <num | range> parameters.

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments:

<prefix>  A prefix for the server names to be built.

<num | range>
          If <num> is provided, this template initializes <num> servers
          with 1 up to <num> as server name suffixes. A range of numbers
          <num_low>-<num_high> may also be used to use <num_low> up to
          <num_high> as server name suffixes.

<fqdn>    A FQDN for all the servers this template initializes.

<port>    Same meaning as "server
This keyword is available in sections :
Alphabetically sorted keywords reference
" <port> argument (see "
This keyword is available in sections :
Peers
" keyword).

<params*>
          Remaining server parameters among all those supported by "server
This keyword is available in sections :
Alphabetically sorted keywords reference
"
          keyword.

Examples:

# Initializes 3 servers with srv1, srv2 and srv3 as names,
# google.com as FQDN, and health-check enabled.
server-template srv 1-3 google.com:80 check

# or
server-template srv 3 google.com:80 check

# would be equivalent to:
server srv1 google.com:80 check
server srv2 google.com:80 check
server srv3 google.com:80 check

[:] [usesrc { [:] | client | clientip } ]

source [:] [usesrc { [:] | hdr_ip([,]) } ]

[:] [interface ]

Set the source address for outgoing connections

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<addr>    is the IPv4 address HAProxy will bind to before connecting to a
          server. This address is also used as a source for health checks.

          The default value of 0.0.0.0 means that the system will select
          the most appropriate address to reach its destination. Optionally
          an address family prefix may be used before the address to force
          the family regardless of the address format, which can be useful
          to specify a path to a unix socket with no slash ('/'). Currently
          supported prefixes are :
            - 'ipv4@' -> address is always IPv4
            - 'ipv6@' -> address is always IPv6
            - 'unix@' -> address is a path to a local unix socket
            - 'abns@' -> address is in abstract namespace (Linux only)
          You may want to reference some environment variables in the
          address parameter, see section 2.3 about environment variables.

<port>    is an optional port. It is normally not needed but may be useful
          in some very specific contexts. The default value of zero means
          the system will select a free port. Note that port ranges are not
          supported in the backend. If you want to force port ranges, you
          have to specify them on each "
This keyword is available in sections :
Peers
" line.

<addr2>   is the IP address to present to the server when connections are
          forwarded in full transparent proxy mode. This is currently only
          supported on some patched Linux kernels. When this address is
          specified, clients connecting to the server will be presented
          with this address, while health checks will still use the address
          <addr>.

<port2>   is the optional port to present to the server when connections
          are forwarded in full transparent proxy mode (see <addr2> above).
          The default value of zero means the system will select a free
          port.

<hdr>     is the name of a HTTP header in which to fetch the IP to bind to.
          This is the name of a comma-separated header list which can
          contain multiple IP addresses. By default, the last occurrence is
          used. This is designed to work with the X-Forwarded-For header
          and to automatically bind to the client's IP address as seen
          by previous proxy, typically Stunnel. In order to use another
          occurrence from the last one, please see the <occ> parameter
          below. When the header (or occurrence) is not found, no binding
          is performed so that the proxy's default IP address is used. Also
          keep in mind that the header name is case insensitive, as for any
          HTTP header.

<occ>     is the occurrence number of a value to be used in a multi-value
          header. This is to be used in conjunction with "hdr_ip(<hdr>)",
          in order to specify which occurrence to use for the source IP
          address. Positive values indicate a position from the first
          occurrence, 1 being the first one. Negative values indicate
          positions relative to the last one, -1 being the last one. This
          is helpful for situations where an X-Forwarded-For header is set
          at the entry point of an infrastructure and must be used several
          proxy layers away. When this value is not specified, -1 is
          assumed. Passing a zero here disables the feature.

<name>    is an optional interface name to which to bind to for outgoing
          traffic. On systems supporting this features (currently, only
          Linux), this allows one to bind all traffic to the server to
          this interface even if it is not the one the system would select
          based on routing tables. This should be used with extreme care.
          Note that using this option requires root privileges.

The "source
This keyword is available in sections :
Server and default-server options
" keyword is useful in complex environments where a specific
address only is allowed to connect to the servers. It may be needed when a
private address must be used through a public gateway for instance, and it is
known that the system cannot determine the adequate source address by itself.

An extension which is available on certain patched Linux kernels may be used
through the "usesrc" optional keyword. It makes it possible to connect to the
servers with an IP address which does not belong to the system itself. This
is called "full transparent proxy mode". For this to work, the destination
servers have to route their traffic back to this address through the machine
running HAProxy, and IP forwarding must generally be enabled on this machine.

In this "full transparent proxy" mode, it is possible to force a specific IP
address to be presented to the servers. This is not much used in fact. A more
common use is to tell HAProxy to present the client's IP address. For this,
there are two methods :

  - present the client's IP and port addresses. This is the most transparent
    mode, but it can cause problems when IP connection tracking is enabled on
    the machine, because a same connection may be seen twice with different
    states. However, this solution presents the huge advantage of not
    limiting the system to the 64k outgoing address+port couples, because all
    of the client ranges may be used.

  - present only the client's IP address and select a spare port. This
    solution is still quite elegant but slightly less transparent (downstream
    firewalls logs will not match upstream's). It also presents the downside
    of limiting the number of concurrent connections to the usual 64k ports.
    However, since the upstream and downstream ports are different, local IP
    connection tracking on the machine will not be upset by the reuse of the
    same session.

This option sets the default source for all servers in the backend. It may
also be specified in a "defaults" section. Finer source address specification
is possible at the server level using the "
This keyword is available in sections :
Alphabetically sorted keywords reference
" server option. Refer to
section 5 for more information.

In order to work, "usesrc" requires root privileges.

Examples :

backend private
    # Connect to the servers using our 192.168.1.200 source address
    source 192.168.1.200

backend transparent_ssl1
    # Connect to the SSL farm from the client's source address
    source 192.168.1.200 usesrc clientip

backend transparent_ssl2
    # Connect to the SSL farm from the client's source address and port
    # not recommended if IP conntrack is present on the local machine.
    source 192.168.1.200 usesrc client

backend transparent_ssl3
    # Connect to the SSL farm from the client's source address. It
    # is more conntrack-friendly.
    source 192.168.1.200 usesrc clientip

backend transparent_smtp
    # Connect to the SMTP farm from the client's source address/port
    # with Tproxy version 4.
    source 0.0.0.0 usesrc clientip

backend transparent_http
    # Connect to the servers using the client's IP as seen by previous
    # proxy.
    source 0.0.0.0 usesrc hdr_ip(x-forwarded-for,-1)

See also : the “

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“ server option in section 5, the Tproxy patches for the Linux kernel on www.balabit.com, the “

• This keyword is available in sections :
• Peers

“ keyword.

srvtimeout (deprecated)

Set the maximum inactivity time on the server side.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the server is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase of the server's response, when it has to send the
headers, as it directly represents the server's processing time for the
request. To find out what value to put there, it's often good to start with
what would be considered as unacceptable response times, then check the logs
to observe the response time distribution, and adjust the value accordingly.

The value is specified in milliseconds by default, but can be in any other
unit if the number is suffixed by the unit, as specified at the top of this
document. In TCP mode (and to a lesser extent, in HTTP mode), it is highly
recommended that the client timeout remains equal to the server timeout in
order to avoid complex situations to debug. Whatever the expected server
response times, it is a good practice to cover at least one or several TCP
packet losses by specifying timeouts that are slightly above multiples of 3
seconds (e.g. 4 or 5 seconds minimum).

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of expired sessions in
the system if the system's timeouts are not configured either.

This parameter is provided for compatibility but is currently deprecated.
Please use "" instead.

See also : “timeout server“, ““, “timeout client“ and ““.

stats admin { if | unless }

Enable statistics admin level if/unless a condition is matched

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

This statement enables the statistics admin level if/unless a condition is
matched.

The admin level allows to enable/disable servers from the web interface. By
default, statistics page is read-only for security reasons.

Note : Consider not using this feature in multi-process mode (nbproc > 1)
       unless you know what you do : memory is not shared between the
       processes, which can result in random behaviors.

Currently, the POST request is limited to the buffer size minus the reserved
buffer space, which means that if the list of servers is too long, the
request won't be processed. It is recommended to alter few servers at a
time.

Example :

# statistics admin level only for localhost
backend stats_localhost
    stats enable
    stats admin if LOCALHOST

Example :

# statistics admin level always enabled because of the authentication
backend stats_auth
    stats enable
    stats auth  admin:AdMiN123
    stats admin if TRUE

Example :

# statistics admin level depends on the authenticated user
userlist stats-auth
    group admin    users admin
    user  admin    insecure-password AdMiN123
    group readonly users haproxy
    user  haproxy  insecure-password haproxy

backend stats_auth
    stats enable
    acl AUTH       http_auth(stats-auth)
    acl AUTH_ADMIN http_auth_group(stats-auth) admin
    stats http-request auth unless AUTH
    stats admin if AUTH_ADMIN

See also : ““, “stats auth“, ““, “nbproc

• This keyword is available in sections :
• Fetching samples from internal states

“, ““, section 3.4 about userlists and about ACL usage.

stats auth :

Enable statistics with authentication and grant access to an account

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<user>    is a user name to grant access to

<passwd>  is the cleartext password associated to this user

This statement enables statistics with default settings, and restricts access
to declared users only. It may be repeated as many times as necessary to
allow as many users as desired. When a user tries to access the statistics
without a valid account, a "401 Forbidden" response will be returned so that
the browser asks the user to provide a valid user and password. The real
which will be returned to the browser is configurable using "".

Since the authentication method is HTTP Basic Authentication, the passwords
circulate in cleartext on the network. Thus, it was decided that the
configuration file would also use cleartext passwords to remind the users
that those ones should not be sensitive and not shared with any other account.

It is also possible to reduce the scope of the proxies which appear in the
report using "stats scope".

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : ““, “stats realm“, ““, “stats uri“

Enable statistics reporting with default settings

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

This statement enables statistics reporting with default settings defined
at build time. Unless stated otherwise, these settings are used :
  - stats uri   : /haproxy?stats
  - stats realm : "HAProxy Statistics"
  - stats auth  : no authentication
  - stats scope : no restriction

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : “stats auth“, ““, “stats uri“

Enable statistics and hide HAProxy version reporting

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

By default, the stats page reports some useful status information along with
the statistics. Among them is HAProxy's version. However, it is generally
considered dangerous to report precise version to anyone, as it can help them
target known weaknesses with specific attacks. The "stats hide-version"
statement removes the version from the statistics report. This is recommended
for public sites or any site with a weak login/password.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : ““, “stats enable“, ““, “stats uri“

{ allow | deny | auth [realm ] } [ { if | unless } ]

Access control for statistics

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

As "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
", these set of options allow to fine control access to
statistics. Each option may be followed by if/unless and acl.
First option with matched condition (or option without condition) is final.
For "deny" a 403 error will be returned, for "allow" normal processing is
performed, for "auth" a 401/407 error code is returned so the client
should be asked to enter a username and password.

There is no fixed limit to the number of http-request statements per
instance.

See also : “

• This keyword is available in sections :
• Proxy section

“, section 3.4 about userlists and about ACL usage.

stats realm

Enable statistics and set authentication realm

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<realm>   is the name of the HTTP Basic Authentication realm reported to
          the browser. The browser uses it to display it in the pop-up
          inviting the user to enter a valid username and password.

The realm is read as a single word, so any spaces in it should be escaped
using a backslash ('\').

This statement is useful only in conjunction with "" since it is
only related to authentication.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : “stats auth“, ““, “stats uri“

Enable statistics with automatic refresh

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<delay>   is the suggested refresh delay, specified in seconds, which will
          be returned to the browser consulting the report page. While the
          browser is free to apply any delay, it will generally respect it
          and refresh the page this every seconds. The refresh interval may
          be specified in any other non-default time unit, by suffixing the
          unit after the value, as explained at the top of this document.

This statement is useful on monitoring displays with a permanent page
reporting the load balancer's activity. When set, the HTML report page will
include a link "refresh"/"stop refresh" so that the user can select whether
he wants automatic refresh of the page or not.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : “stats auth“, ““, “stats realm“, ““

stats scope { | “.” }

Enable statistics and limit access scope

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<name>    is the name of a listen, frontend or backend section to be
          reported. The special name "." (a single dot) designates the
          section in which the statement appears.

When this statement is specified, only the sections enumerated with this
statement will appear in the report. All other ones will be hidden. This
statement may appear as many times as needed if multiple sections need to be
reported. Please note that the name checking is performed as simple string
comparisons, and that it is never checked that a give section name really
exists.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : ““, “stats enable“, ““, “stats uri“

[ ]

Enable reporting of a description on the statistics page.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

  <desc>    is an optional description to be reported. If unspecified, the
            description from global section is automatically used instead.

This statement is useful for users that offer shared services to their
customers, where node or description should be different for each customer.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters. By default description is not shown.

Example :

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats show-desc Master node for Europe, Asia, Africa
    stats uri       /admin?stats
    stats refresh   5s

See also: “show-node”, “stats enable“, ““ and “description

• This keyword is available in sections :
• Alphabetically sorted keywords reference

“ in global section.

Enable reporting additional information on the statistics page

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments : none

Enable reporting additional information on the statistics page :
  - cap: capabilities (proxy)
  - mode: one of tcp, http or health (proxy)
  - id: SNMP ID (proxy, socket, server)
  - IP (socket, server)
  - cookie (backend, server)

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters. Default behavior is not to show this information.

See also: “stats enable“, ““.

stats show-node [ ]

Enable reporting of a host name on the statistics page.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments:

<name>    is an optional name to be reported. If unspecified, the
          node name from global section is automatically used instead.

This statement is useful for users that offer shared services to their
customers, where node or description might be different on a stats page
provided for each customer. Default behavior is not to show host name.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example:

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats show-node Europe-1
    stats uri       /admin?stats
    stats refresh   5s

See also: “show-desc”, ““, “stats uri“, and ““ in global section.

stats uri

Enable statistics and define the URI prefix to access them

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<prefix>  is the prefix of any URI which will be redirected to stats. This
          prefix may contain a question mark ('?') to indicate part of a
          query string.

The statistics URI is intercepted on the relayed traffic, so it appears as a
page within the normal application. It is strongly advised to ensure that the
selected URI will never appear in the application, otherwise it will never be
possible to reach it in the application.

The default URI compiled in haproxy is "/haproxy?stats", but this may be
changed at build time, so it's better to always explicitly specify it here.
It is generally a good idea to include a question mark in the URI so that
intermediate proxies refrain from caching the results. Also, since any string
beginning with the prefix will be accepted as a stats request, the question
mark helps ensuring that no valid URI will begin with the same words.

It is sometimes very convenient to use "/" as the URI prefix, and put that
statement in a "listen" instance of its own. That makes it easy to dedicate
an address or a port to statistics only.

Though this statement alone is enough to enable statistics reporting, it is
recommended to set all other settings in order to avoid relying on default
unobvious parameters.

Example :

# public access (limited to this backend only)
backend public_www
    server srv1 192.168.0.1:80
    stats enable
    stats hide-version
    stats scope   .
    stats uri     /admin?stats
    stats realm   HAProxy\ Statistics
    stats auth    admin1:AdMiN123
    stats auth    admin2:AdMiN321

# internal monitoring access (unlimited)
backend private_monitoring
    stats enable
    stats uri     /admin?stats
    stats refresh 5s

See also : ““, “stats enable“, ““

stick match [table

] [{if | unless} ]

Define a request pattern matching condition to stick a user to a server

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<pattern>  is a sample expression rule as described in . It
           describes what elements of the incoming request or connection
           will be analyzed in the hope to find a matching entry in a
           stickiness table. This rule is mandatory.

<table>    is an optional stickiness table name. If unspecified, the same
           backend's table is used. A stickiness table is declared using
           the "stick-table" statement.

<cond>     is an optional matching condition. It makes it possible to match
           on a certain criterion only when other conditions are met (or
           not met). For instance, it could be used to match on a source IP
           address except when a request passes through a known proxy, in
           which case we'd match on a header containing that IP address.

Some protocols or applications require complex stickiness rules and cannot
always simply rely on cookies nor hashing. The "" statement
describes a rule to extract the stickiness criterion from an incoming request
or connection. See section 7 for a complete list of possible patterns and
transformation rules.

The table has to be declared using the "" statement. It must be of
a type compatible with the pattern. By default it is the one which is present
in the same backend. It is possible to share a table with other backends by
referencing it using the "table" keyword. If another table is referenced,
the server's ID inside the backends are used. By default, all server IDs
start at 1 in each backend, so the server ordering is enough. But in case of
doubt, it is highly recommended to force server IDs using their "
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options
" setting.

It is possible to restrict the conditions where a "" statement
will apply, using "if" or "unless" followed by a condition. See section 7 for
ACL based conditions.

There is no limit on the number of "" statements. The first that
applies and matches will cause the request to be directed to the same server
as was used for the request which created the entry. That way, multiple
matches can be used as fallbacks.

The stick rules are checked after the persistence cookies, so they will not
affect stickiness if a cookie has already been used to select a server. That
way, it becomes very easy to insert cookies and match on IP addresses in
order to maintain stickiness between HTTP and HTTPS.

Note : Consider not using this feature in multi-process mode (nbproc > 1)
       unless you know what you do : memory is not shared between the
       processes, which can result in random behaviors.

Example :

# forward SMTP users to the same server they just used for POP in the
# last 30 minutes
backend pop
    mode tcp
    balance roundrobin
    stick store-request src
    stick-table type ip size 200k expire 30m
    server s1 192.168.1.1:110
    server s2 192.168.1.1:110

backend smtp
    mode tcp
    balance roundrobin
    stick match src table pop
    server s1 192.168.1.1:25
    server s2 192.168.1.1:25

See also : “stick-table“, ““, “nbproc

• This keyword is available in sections :
• Fetching samples from internal states

“, ““ and section 7 about ACLs and samples fetching.

[table

] [{if | unless} ]

Define a request pattern to associate a user to a server

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Note : This form is exactly equivalent to "stick match" followed by
       "", all with the same arguments. Please refer
       to both keywords for details. It is only provided as a convenience
       for writing more maintainable configurations.

Note : Consider not using this feature in multi-process mode (nbproc > 1)
       unless you know what you do : memory is not shared between the
       processes, which can result in random behaviors.

Examples :

# The following form ...
stick on src table pop if !localhost

# ...is strictly equivalent to this one :
stick match src table pop if !localhost
stick store-request src table pop if !localhost


# Use cookie persistence for HTTP, and stick on source address for HTTPS as
# well as HTTP without cookie. Share the same table between both accesses.
backend http
    mode http
    balance roundrobin
    stick on src table https
    cookie SRV insert indirect nocache
    server s1 192.168.1.1:80 cookie s1
    server s2 192.168.1.1:80 cookie s2

backend https
    mode tcp
    balance roundrobin
    stick-table type ip size 200k expire 30m
    stick on src
    server s1 192.168.1.1:443
    server s2 192.168.1.1:443

See also : “stick match“, ““, “nbproc

• This keyword is available in sections :
• Fetching samples from internal states

“ and ““.

stick store-request [table

] [{if | unless} ]

Define a request pattern used to create an entry in a stickiness table

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<pattern>  is a sample expression rule as described in . It
           describes what elements of the incoming request or connection
           will be analyzed, extracted and stored in the table once a
           server is selected.

<table>    is an optional stickiness table name. If unspecified, the same
           backend's table is used. A stickiness table is declared using
           the "stick-table" statement.

<cond>     is an optional storage condition. It makes it possible to store
           certain criteria only when some conditions are met (or not met).
           For instance, it could be used to store the source IP address
           except when the request passes through a known proxy, in which
           case we'd store a converted form of a header containing that IP
           address.

Some protocols or applications require complex stickiness rules and cannot
always simply rely on cookies nor hashing. The "" statement
describes a rule to decide what to extract from the request and when to do
it, in order to store it into a stickiness table for further requests to
match it using the "stick match" statement. Obviously the extracted part must
make sense and have a chance to be matched in a further request. Storing a
client's IP address for instance often makes sense. Storing an ID found in a
URL parameter also makes sense. Storing a source port will almost never make
any sense because it will be randomly matched. See  for a complete
list of possible patterns and transformation rules.

The table has to be declared using the "stick-table" statement. It must be of
a type compatible with the pattern. By default it is the one which is present
in the same backend. It is possible to share a table with other backends by
referencing it using the "" keyword. If another table is referenced,
the server's ID inside the backends are used. By default, all server IDs
start at 1 in each backend, so the server ordering is enough. But in case of
doubt, it is highly recommended to force server IDs using their "id
This keyword is available in sections :
Bind options
" setting.

It is possible to restrict the conditions where a "stick store-request"
statement will apply, using "if" or "unless" followed by a condition. This
condition will be evaluated while parsing the request, so any criteria can be
used. See  for ACL based conditions.

There is no limit on the number of "stick store-request" statements, but
there is a limit of 8 simultaneous stores per request or response. This
makes it possible to store up to 8 criteria, all extracted from either the
request or the response, regardless of the number of rules. Only the 8 first
ones which match will be kept. Using this, it is possible to feed multiple
tables at once in the hope to increase the chance to recognize a user on
another protocol or access method. Using multiple store-request rules with
the same table is possible and may be used to find the best criterion to rely
on, by arranging the rules by decreasing preference order. Only the first
extracted criterion for a given table will be stored. All subsequent store-
request rules referencing the same table will be skipped and their ACLs will
not be evaluated.

The "store-request" rules are evaluated once the server connection has been
established, so that the table will contain the real server that processed
the request.

Note : Consider not using this feature in multi-process mode (nbproc > 1)
       unless you know what you do : memory is not shared between the
       processes, which can result in random behaviors.

Example :

# forward SMTP users to the same server they just used for POP in the
# last 30 minutes
backend pop
    mode tcp
    balance roundrobin
    stick store-request src
    stick-table type ip size 200k expire 30m
    server s1 192.168.1.1:110
    server s2 192.168.1.1:110

backend smtp
    mode tcp
    balance roundrobin
    stick match src table pop
    server s1 192.168.1.1:25
    server s2 192.168.1.1:25

See also : ““, “stick on“, “

• This keyword is available in sections :
• Process management and security

“, “bind-process“ and about ACLs and sample fetching.

stick-table type {ip | integer | string [len ] | binary [len ]} size [expire ] [nopurge] [peers ] [store ]*

Configure the stickiness table for the current section

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

 ip         a table declared with "type ip" will only store IPv4 addresses.
            This form is very compact (about 50 bytes per entry) and allows
            very fast entry lookup and stores with almost no overhead. This
            is mainly used to store client source IP addresses.

 ipv6       a table declared with "type ipv6" will only store IPv6 addresses.
            This form is very compact (about 60 bytes per entry) and allows
            very fast entry lookup and stores with almost no overhead. This
            is mainly used to store client source IP addresses.

 integer    a table declared with "type integer" will store 32bit integers
            which can represent a client identifier found in a request for
            instance.

 string     a table declared with "type string" will store substrings of up
            to <len> characters. If the string provided by the pattern
            extractor is larger than <len>, it will be truncated before
            being stored. During matching, at most <len> characters will be
            compared between the string in the table and the extracted
            pattern. When not specified, the string is automatically limited
            to 32 characters.

 binary     a table declared with "type binary" will store binary blocks
            of <len> bytes. If the block provided by the pattern
            extractor is larger than <len>, it will be truncated before
            being stored. If the block provided by the sample expression
            is shorter than <len>, it will be padded by 0. When not
            specified, the block is automatically limited to 32 bytes.

 <length>   is the maximum number of characters that will be stored in a
            "string" type table (See type "string" above). Or the number
            of bytes of the block in "binary" type table. Be careful when
            changing this parameter as memory usage will proportionally
            increase.

 <size>     is the maximum number of entries that can fit in the table. This
            value directly impacts memory usage. Count approximately
            50 bytes per entry, plus the size of a string if any. The size
            supports suffixes "k", "m", "g" for 2^10, 2^20 and 2^30 factors.

 [nopurge]  indicates that we refuse to purge older entries when the table
            is full. When not specified and the table is full when haproxy
            wants to store an entry in it, it will flush a few of the oldest
            entries in order to release some space for the new ones. This is
            most often the desired behavior. In some specific cases, it
            be desirable to refuse new entries instead of purging the older
            ones. That may be the case when the amount of data to store is
            far above the hardware limits and we prefer not to offer access
            to new clients than to reject the ones already connected. When
            using this parameter, be sure to properly set the "expire"
            parameter (see below).

 <peersect> is the name of the peers section to use for replication. Entries
            which associate keys to server IDs are kept synchronized with
            the remote peers declared in this section. All entries are also
            automatically learned from the local peer (old process) during a
            soft restart.

            NOTE : each peers section may be referenced only by tables
                   belonging to the same unique process.

 <expire>   defines the maximum duration of an entry in the table since it
            was last created, refreshed or matched. The expiration delay is
            defined using the standard time format, similarly as the various
            timeouts. The maximum duration is slightly above 24 days. See
             for more information. If this delay is not specified,
            the session won't automatically expire, but older entries will
            be removed once full. Be sure not to use the "nopurge" parameter
            if not expiration delay is specified.

<data_type> is used to store additional information in the stick-table. This
            may be used by ACLs in order to control various criteria related
            to the activity of the client matching the stick-table. For each
            item specified here, the size of each entry will be inflated so
            that the additional data can fit. Several data types may be
            stored with an entry. Multiple data types may be specified after
            the "store" keyword, as a comma-separated list. Alternatively,
            it is possible to repeat the "store" keyword followed by one or
            several data types. Except for the "server_id" type which is
            automatically detected and enabled, all data types must be
            explicitly declared to be stored. If an ACL references a data
            type which is not stored, the ACL will simply not match. Some
            data types require an argument which must be passed just after
            the type between parenthesis. See below for the supported data
            types and their arguments.

The data types that can be stored with an entry are the following :
  - server_id : this is an integer which holds the numeric ID of the server a
    request was assigned to. It is used by the "stick match", "stick store",
    and "" rules. It is automatically enabled when referenced.

  - gpc0 : first General Purpose Counter. It is a positive 32-bit integer
    integer which may be used for anything. Most of the time it will be used
    to put a special tag on some entries, for instance to note that a
    specific behavior was detected and must be known for future matches.

  - gpc0_rate(<period>) : increment rate of the first General Purpose Counter
    over a period. It is a positive 32-bit integer integer which may be used
    for anything. Just like <gpc0>, it counts events, but instead of keeping
    a cumulative number, it maintains the rate at which the counter is
    incremented. Most of the time it will be used to measure the frequency of
    occurrence of certain events (e.g. requests to a specific URL).

  - gpc1 : second General Purpose Counter. It is a positive 32-bit integer
    integer which may be used for anything. Most of the time it will be used
    to put a special tag on some entries, for instance to note that a
    specific behavior was detected and must be known for future matches.

  - gpc1_rate(<period>) : increment rate of the second General Purpose Counter
    over a period. It is a positive 32-bit integer integer which may be used
    for anything. Just like <gpc1>, it counts events, but instead of keeping
    a cumulative number, it maintains the rate at which the counter is
    incremented. Most of the time it will be used to measure the frequency of
    occurrence of certain events (e.g. requests to a specific URL).

  - conn_cnt : Connection Count. It is a positive 32-bit integer which counts
    the absolute number of connections received from clients which matched
    this entry. It does not mean the connections were accepted, just that
    they were received.

  - conn_cur : Current Connections. It is a positive 32-bit integer which
    stores the concurrent connection counts for the entry. It is incremented
    once an incoming connection matches the entry, and decremented once the
    connection leaves. That way it is possible to know at any time the exact
    number of concurrent connections for an entry.

  - conn_rate(<period>) : frequency counter (takes 12 bytes). It takes an
    integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    incoming connection rate over that period, in connections per period. The
    result is an integer which can be matched using ACLs.

  - sess_cnt : Session Count. It is a positive 32-bit integer which counts
    the absolute number of sessions received from clients which matched this
    entry. A session is a connection that was accepted by the layer 4 rules.

  - sess_rate(<period>) : frequency counter (takes 12 bytes). It takes an
    integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    incoming session rate over that period, in sessions per period. The
    result is an integer which can be matched using ACLs.

  - http_req_cnt : HTTP request Count. It is a positive 32-bit integer which
    counts the absolute number of HTTP requests received from clients which
    matched this entry. It does not matter whether they are valid requests or
    not. Note that this is different from sessions when keep-alive is used on
    the client side.

  - http_req_rate(<period>) : frequency counter (takes 12 bytes). It takes an
    integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    HTTP request rate over that period, in requests per period. The result is
    an integer which can be matched using ACLs. It does not matter whether
    they are valid requests or not. Note that this is different from sessions
    when keep-alive is used on the client side.

  - http_err_cnt : HTTP Error Count. It is a positive 32-bit integer which
    counts the absolute number of HTTP requests errors induced by clients
    which matched this entry. Errors are counted on invalid and truncated
    requests, as well as on denied or tarpitted requests, and on failed
    authentications. If the server responds with 4xx, then the request is
    also counted as an error since it's an error triggered by the client
    (e.g. vulnerability scan).

  - http_err_rate(<period>) : frequency counter (takes 12 bytes). It takes an
    integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    HTTP request error rate over that period, in requests per period (see
    http_err_cnt above for what is accounted as an error). The result is an
    integer which can be matched using ACLs.

  - bytes_in_cnt : client to server byte count. It is a positive 64-bit
    integer which counts the cumulative number of bytes received from clients
    which matched this entry. Headers are included in the count. This may be
    used to limit abuse of upload features on photo or video servers.

  - bytes_in_rate(<period>) : frequency counter (takes 12 bytes). It takes an
    integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    incoming bytes rate over that period, in bytes per period. It may be used
    to detect users which upload too much and too fast. Warning: with large
    uploads, it is possible that the amount of uploaded data will be counted
    once upon termination, thus causing spikes in the average transfer speed
    instead of having a smooth one. This may partially be smoothed with
    "option contstats" though this is not perfect yet. Use of byte_in_cnt is
    recommended for better fairness.

  - bytes_out_cnt : server to client byte count. It is a positive 64-bit
    integer which counts the cumulative number of bytes sent to clients which
    matched this entry. Headers are included in the count. This may be used
    to limit abuse of bots sucking the whole site.

  - bytes_out_rate(<period>) : frequency counter (takes 12 bytes). It takes
    an integer parameter <period> which indicates in milliseconds the length
    of the period over which the average is measured. It reports the average
    outgoing bytes rate over that period, in bytes per period. It may be used
    to detect users which download too much and too fast. Warning: with large
    transfers, it is possible that the amount of transferred data will be
    counted once upon termination, thus causing spikes in the average
    transfer speed instead of having a smooth one. This may partially be
    smoothed with "" though this is not perfect yet. Use of
    byte_out_cnt is recommended for better fairness.

There is only one stick-table per proxy. At the moment of writing this doc,
it does not seem useful to have multiple tables per proxy. If this happens
to be required, simply create a dummy backend with a stick-table in it and
reference it.

It is important to understand that stickiness based on learning information
has some limitations, including the fact that all learned associations are
lost upon restart unless peers are properly configured to transfer such
information upon restart (recommended). In general it can be good as a
complement but not always as an exclusive stickiness.

Last, memory requirements may be important when storing many data types.
Indeed, storing all indicators above at once in each entry requires 116 bytes
per entry, or 116 MB for a 1-million entries table. This is definitely not
something that can be ignored.

Example:

# Keep track of counters of up to 1 million IP addresses over 5 minutes
# and store a general purpose counter and the average connection rate
# computed over a sliding window of 30 seconds.
stick-table type ip size 1m expire 5m store gpc0,conn_rate(30s)

See also : “stick match“, ““, “stick store-request“, about time format and section 7 about ACLs.

[table

] [{if | unless} ]

Define a response pattern used to create an entry in a stickiness table

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<pattern>  is a sample expression rule as described in section 7.3. It
           describes what elements of the response or connection will
           be analyzed, extracted and stored in the table once a
           server is selected.

<table>    is an optional stickiness table name. If unspecified, the same
           backend's table is used. A stickiness table is declared using
           the "" statement.

<cond>     is an optional storage condition. It makes it possible to store
           certain criteria only when some conditions are met (or not met).
           For instance, it could be used to store the SSL session ID only
           when the response is a SSL server hello.

Some protocols or applications require complex stickiness rules and cannot
always simply rely on cookies nor hashing. The "stick store-response"
statement  describes a rule to decide what to extract from the response and
when to do it, in order to store it into a stickiness table for further
requests to match it using the "" statement. Obviously the
extracted part must make sense and have a chance to be matched in a further
request. Storing an ID found in a header of a response makes sense.
See section 7 for a complete list of possible patterns and transformation
rules.

The table has to be declared using the "" statement. It must be of
a type compatible with the pattern. By default it is the one which is present
in the same backend. It is possible to share a table with other backends by
referencing it using the "table" keyword. If another table is referenced,
the server's ID inside the backends are used. By default, all server IDs
start at 1 in each backend, so the server ordering is enough. But in case of
doubt, it is highly recommended to force server IDs using their "
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options
" setting.

It is possible to restrict the conditions where a ""
statement will apply, using "if" or "unless" followed by a condition. This
condition will be evaluated while parsing the response, so any criteria can
be used. See section 7 for ACL based conditions.

There is no limit on the number of "" statements, but
there is a limit of 8 simultaneous stores per request or response. This
makes it possible to store up to 8 criteria, all extracted from either the
request or the response, regardless of the number of rules. Only the 8 first
ones which match will be kept. Using this, it is possible to feed multiple
tables at once in the hope to increase the chance to recognize a user on
another protocol or access method. Using multiple store-response rules with
the same table is possible and may be used to find the best criterion to rely
on, by arranging the rules by decreasing preference order. Only the first
extracted criterion for a given table will be stored. All subsequent store-
response rules referencing the same table will be skipped and their ACLs will
not be evaluated. However, even if a store-request rule references a table, a
store-response rule may also use the same table. This means that each table
may learn exactly one element from the request and one element from the
response at once.

The table will contain the real server that processed the request.

Example :

# Learn SSL session ID from both request and response and create affinity.
backend https
    mode tcp
    balance roundrobin
    # maximum SSL session ID length is 32 bytes.
    stick-table type binary len 32 size 30k expire 30m

    acl clienthello req_ssl_hello_type 1
    acl serverhello rep_ssl_hello_type 2

    # use tcp content accepts to detects ssl client and server hello.
    tcp-request inspect-delay 5s
    tcp-request content accept if clienthello

    # no timeout on response inspect delay by default.
    tcp-response content accept if serverhello

    # SSL session ID (SSLID) may be present on a client or server hello.
    # Its length is coded on 1 byte at offset 43 and its value starts
    # at offset 44.

    # Match and learn on request if client hello.
    stick on payload_lv(43,1) if clienthello

    # Learn on response if server hello.
    stick store-response payload_lv(43,1) if serverhello

    server s1 192.168.1.1:443
    server s2 192.168.1.1:443

See also : “stick-table“, ““, and section 7 about ACLs and pattern extraction.

[params*]

Opens a new connection

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

When an application lies on more than a single TCP port or when HAProxy
load-balance many services in a single backend, it makes sense to probe all
the services individually before considering a server as operational.

When there are no TCP port configured on the server line neither server port
directive, then the 'tcp-check connect port <port>' must be the first step
of the sequence.

In a tcp-check ruleset a 'connect' is required, it is also mandatory to start
the ruleset with a 'connect' rule. Purpose is to ensure admin know what they
do.

Parameters :
  They are optional and can be used to describe how HAProxy should open and
  use the TCP connection.

  port      if not set, check port or server port is used.
            It tells HAProxy where to open the connection to.
            <port> must be a valid TCP port source integer, from 1 to 65535.

  send-proxy   send a PROXY protocol string

  ssl          opens a ciphered connection

Examples:

# check HTTP and HTTPs services on a server.
# first open port 80 thanks to server line port directive, then
# tcp-check opens port 443, ciphered and run a request on it:
option tcp-check
tcp-check connect
tcp-check send GET\ /\ HTTP/1.0\r\n
tcp-check send Host:\ haproxy.1wt.eu\r\n
tcp-check send \r\n
tcp-check expect rstring (2..|3..)
tcp-check connect port 443 ssl
tcp-check send GET\ /\ HTTP/1.0\r\n
tcp-check send Host:\ haproxy.1wt.eu\r\n
tcp-check send \r\n
tcp-check expect rstring (2..|3..)
server www 10.0.0.1 check port 80

# check both POP and IMAP from a single server:
option tcp-check
tcp-check connect port 110
tcp-check expect string +OK\ POP3\ ready
tcp-check connect port 143
tcp-check expect string *\ OK\ IMAP4\ ready
server mail 10.0.0.1 check

See also : “option tcp-check“, ““, “tcp-check expect“

[!]

Specify data to be collected and analyzed during a generic health check

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<match>   is a keyword indicating how to look for a specific pattern in the
          response. The keyword may be one of "string", "rstring" or
          binary.
          The keyword may be preceded by an exclamation mark ("!") to negate
          the match. Spaces are allowed between the exclamation mark and the
          keyword. See below for more details on the supported keywords.

<pattern> is the pattern to look for. It may be a string or a regular
          expression. If the pattern contains spaces, they must be escaped
          with the usual backslash ('\').
          If the match is set to binary, then the pattern must be passed as
          a series of hexadecimal digits in an even number. Each sequence of
          two digits will represent a byte. The hexadecimal digits may be
          used upper or lower case.

The available matches are intentionally similar to their http-check cousins :

  string <string> : test the exact string matches in the response buffer.
                    A health check response will be considered valid if the
                    response's buffer contains this exact string. If the
                    "string" keyword is prefixed with "!", then the response
                    will be considered invalid if the body contains this
                    string. This can be used to look for a mandatory pattern
                    in a protocol response, or to detect a failure when a
                    specific error appears in a protocol banner.

  rstring <regex> : test a regular expression on the response buffer.
                    A health check response will be considered valid if the
                    response's buffer matches this expression. If the
                    "rstring" keyword is prefixed with "!", then the response
                    will be considered invalid if the body matches the
                    expression.

  binary <hexstring> : test the exact string in its hexadecimal form matches
                       in the response buffer. A health check response will
                       be considered valid if the response's buffer contains
                       this exact hexadecimal string.
                       Purpose is to match data on binary protocols.

It is important to note that the responses will be limited to a certain size
defined by the global "tune.chksize" option, which defaults to 16384 bytes.
Thus, too large responses may not contain the mandatory pattern when using
"string", "rstring" or binary. If a large response is absolutely required, it
is possible to change the default max size by setting the global variable.
However, it is worth keeping in mind that parsing very large responses can
waste some CPU cycles, especially when regular expressions are used, and that
it is always better to focus the checks on smaller resources. Also, in its
current state, the check will not find any string nor regex past a null
character in the response. Similarly it is not possible to request matching
the null character.

Examples :

# perform a POP check
option tcp-check
tcp-check expect string +OK\ POP3\ ready

# perform an IMAP check
option tcp-check
tcp-check expect string *\ OK\ IMAP4\ ready

# look for the redis master server
option tcp-check
tcp-check send PING\r\n
tcp-check expect string +PONG
tcp-check send info\ replication\r\n
tcp-check expect string role:master
tcp-check send QUIT\r\n
tcp-check expect string +OK

See also : ““, “tcp-check connect“, ““, “tcp-check send-binary“, ““, tune.chksize

tcp-check send

Specify a string to be sent as a question during a generic health check

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

<data> : the data to be sent as a question during a generic health check
         session. For now, <data> must be a string.

Examples :

# look for the redis master server
option tcp-check
tcp-check send info\ replication\r\n
tcp-check expect string role:master

See also : ““, “tcp-check connect“, ““, “tcp-check send-binary“, tune.chksize

Specify a hex digits string to be sent as a binary question during a raw
tcp health check

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

<data> : the data to be sent as a question during a generic health check
         session. For now, <data> must be a string.
<hexstring> : test the exact string in its hexadecimal form matches in the
               response buffer. A health check response will be considered
               valid if the response's buffer contains this exact
               hexadecimal string.
               Purpose is to send binary data to ask on binary protocols.

Examples :

# redis check in binary
option tcp-check
tcp-check send-binary 50494e470d0a # PING\r\n
tcp-check expect binary 2b504F4e47 # +PONG

See also : “option tcp-check“, ““, “tcp-check expect“, ““, tune.chksize

tcp-request connection [{if | unless} ]

Perform an action on an incoming connection depending on a layer 4 condition

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<action>    defines the action to perform if the condition applies. See
            below.

<condition> is a standard layer4-only ACL-based condition (see ).

Immediately after acceptance of a new incoming connection, it is possible to
evaluate some conditions to decide whether this connection must be accepted
or dropped or have its counters tracked. Those conditions cannot make use of
any data contents because the connection has not been read from yet, and the
buffers are not yet allocated. This is used to selectively and very quickly
accept or drop connections from various sources with a very low overhead. If
some contents need to be inspected in order to take the decision, the
"tcp-request content" statements must be used instead.

The "" rules are evaluated in their exact declaration
order. If no rule matches or if there is no rule, the default action is to
accept the incoming connection. There is no specific limit to the number of
rules which may be inserted.

Four types of actions are supported :
  - accept :
      accepts the connection if the condition is true (when used with "if")
      or false (when used with "unless"). The first such rule executed ends
      the rules evaluation.

  - reject :
      rejects the connection if the condition is true (when used with "if")
      or false (when used with "unless"). The first such rule executed ends
      the rules evaluation. Rejected connections do not even become a
      session, which is why they are accounted separately for in the stats,
      as "denied connections". They are not considered for the session
      rate-limit and are not logged either. The reason is that these rules
      should only be used to filter extremely high connection rates such as
      the ones encountered during a massive DDoS attack. Under these extreme
      conditions, the simple action of logging each event would make the
      system collapse and would considerably lower the filtering capacity. If
      logging is absolutely desired, then "tcp-request content" rules should
      be used instead, as "" rules will not log either.

  - expect-proxy layer4 :
      configures the client-facing connection to receive a PROXY protocol
      header before any byte is read from the socket. This is equivalent to
      having the "accept-proxy" keyword on the "
This keyword is available in sections :
Peers
" line, except that using
      the TCP rule allows the PROXY protocol to be accepted only for certain
      IP address ranges using an ACL. This is convenient when multiple layers
      of load balancers are passed through by traffic coming from public
      hosts.

  - expect-netscaler-cip layer4 :
      configures the client-facing connection to receive a NetScaler Client
      IP insertion protocol header before any byte is read from the socket.
      This is equivalent to having the "accept-netscaler-cip" keyword on the
      "
This keyword is available in sections :
Peers
" line, except that using the TCP rule allows the PROXY protocol
      to be accepted only for certain IP address ranges using an ACL. This
      is convenient when multiple layers of load balancers are passed
      through by traffic coming from public hosts.

  - capture <sample> len <length> :
      This only applies to "tcp-request content" rules. It captures sample
      expression <sample> from the request buffer, and converts it to a
      string of at most <len> characters. The resulting string is stored into
      the next request "" slot, so it will possibly appear next to
      some captured HTTP headers. It will then automatically appear in the
      logs, and it will be possible to extract it using sample fetch rules to
      feed it into headers or anything. The length should be limited given
      that this size will be allocated for each capture during the whole
      session life. Please check section 7.3 (Fetching samples) and "capture
      request header" for more information.

  - { track-sc0 | track-sc1 | track-sc2 } <key> [table <table>] :
      enables tracking of sticky counters from current connection. These
      rules do not stop evaluation and do not change default action. The
      number of counters that may be simultaneously tracked by the same
      connection is set in MAX_SESS_STKCTR at build time (reported in
      haproxy -vv) which defaults to 3, so the track-sc number is between 0
      and (MAX_SESS_STCKTR-1). The first "track-sc0" rule executed enables
      tracking of the counters of the specified table as the first set. The
      first "track-sc1" rule executed enables tracking of the counters of the
      specified table as the second set. The first "track-sc2" rule executed
      enables tracking of the counters of the specified table as the third
      set. It is a recommended practice to use the first set of counters for
      the per-frontend counters and the second set for the per-backend ones.
      But this is just a guideline, all may be used everywhere.

      These actions take one or two arguments :
        <key>   is mandatory, and is a sample expression rule as described
                in . It describes what elements of the incoming
                request or connection will be analyzed, extracted, combined,
                and used to select which table entry to update the counters.
                Note that "tcp-request connection" cannot use content-based
                fetches.

       <table>  is an optional table to be used instead of the default one,
                which is the stick-table declared in the current proxy. All
                the counters for the matches and updates for the key will
                then be performed in that table until the session ends.

      Once a "track-sc*" rule is executed, the key is looked up in the table
      and if it is not found, an entry is allocated for it. Then a pointer to
      that entry is kept during all the session's life, and this entry's
      counters are updated as often as possible, every time the session's
      counters are updated, and also systematically when the session ends.
      Counters are only updated for events that happen after the tracking has
      been started. For example, connection counters will not be updated when
      tracking layer 7 information, since the connection event happens before
      layer7 information is extracted.

      If the entry tracks concurrent connection counters, one connection is
      counted for as long as the entry is tracked, and the entry will not
      expire during that time. Tracking counters also provides a performance
      advantage over just checking the keys, because only one table lookup is
      performed for all ACL checks that make use of it.

  - sc-inc-gpc0(<sc-id>):
      The "sc-inc-gpc0" increments the GPC0 counter according to the sticky
      counter designated by <sc-id>. If an error occurs, this action silently
      fails and the actions evaluation continues.

  - sc-inc-gpc1(<sc-id>):
      The "sc-inc-gpc1" increments the GPC1 counter according to the sticky
      counter designated by <sc-id>. If an error occurs, this action silently
      fails and the actions evaluation continues.

  - sc-set-gpt0(<sc-id>) <int>:
      This action sets the GPT0 tag according to the sticky counter designated
      by <sc-id> and the value of <int>. The expected result is a boolean. If
      an error occurs, this action silently fails and the actions evaluation
      continues.

  - set-src <expr> :
    Is used to set the source IP address to the value of specified
    expression. Useful if you want to mask source IP for privacy.
    If you want to provide an IP from a HTTP header use "http-request
    set-src".

Arguments:

<expr>  Is a standard HAProxy expression formed by a sample-fetch
        followed by some converters.

Example:

tcp-request connection set-src src,ipmask(24)

  When possible, set-src preserves the original source port as long as the
  address family allows it, otherwise the source port is set to 0.

- set-src-port <expr> :
  Is used to set the source port address to the value of specified
  expression.

Arguments:

<expr>  Is a standard HAProxy expression formed by a sample-fetch
        followed by some converters.

Example:

tcp-request connection set-src-port int(4000)

  When possible, set-src-port preserves the original source address as long
  as the address family supports a port, otherwise it forces the source
  address to IPv4 "0.0.0.0" before rewriting the port.

- set-dst <expr> :
  Is used to set the destination IP address to the value of specified
  expression. Useful if you want to mask IP for privacy in log.
  If you want to provide an IP from a HTTP header use "http-request
  set-dst". If you want to connect to the new address/port, use
  '0.0.0.0:0' as a server address in the backend.

     <expr>    Is a standard HAProxy expression formed by a sample-fetch
               followed by some converters.

Example:

tcp-request connection set-dst dst,ipmask(24)
tcp-request connection set-dst ipv4(10.0.0.1)

  When possible, set-dst preserves the original destination port as long as
  the address family allows it, otherwise the destination port is set to 0.

- set-dst-port <expr> :
  Is used to set the destination port address to the value of specified
  expression. If you want to connect to the new address/port, use
  '0.0.0.0:0' as a server address in the backend.


     <expr>    Is a standard HAProxy expression formed by a sample-fetch
               followed by some converters.

Example:

tcp-request connection set-dst-port int(4000)

    When possible, set-dst-port preserves the original destination address as
    long as the address family supports a port, otherwise it forces the
    destination address to IPv4 "0.0.0.0" before rewriting the port.

  - "silent-drop" :
      This stops the evaluation of the rules and makes the client-facing
      connection suddenly disappear using a system-dependent way that tries
      to prevent the client from being notified. The effect it then that the
      client still sees an established connection while there's none on
      HAProxy. The purpose is to achieve a comparable effect to "tarpit"
      except that it doesn't use any local resource at all on the machine
      running HAProxy. It can resist much higher loads than "tarpit", and
      slow down stronger attackers. It is important to understand the impact
      of using this mechanism. All stateful equipment placed between the
      client and HAProxy (firewalls, proxies, load balancers) will also keep
      the established connection for a long time and may suffer from this
      action. On modern Linux systems running with enough privileges, the
      TCP_REPAIR socket option is used to block the emission of a TCP
      reset. On other systems, the socket's TTL is reduced to 1 so that the
      TCP reset doesn't pass the first router, though it's still delivered to
      local networks. Do not use it unless you fully understand how it works.

Note that the "if/unless" condition is optional. If no condition is set on
the action, it is simply performed unconditionally. That can be useful for
"track-sc*" actions as well as for changing the default action to a reject.

Example:

Accept all connections from white-listed hosts, reject too fast connection without counting them, and track accepted connections. This results in connection rate being capped from abusive sources.
tcp-request connection accept if { src -f /etc/haproxy/whitelist.lst }
tcp-request connection reject if { src_conn_rate gt 10 }
tcp-request connection track-sc0 src

Example:

Accept all connections from white-listed hosts, count all other connections and reject too fast ones. This results in abusive ones being blocked as long as they don't slow down.
tcp-request connection accept if { src -f /etc/haproxy/whitelist.lst }
tcp-request connection track-sc0 src
tcp-request connection reject if { sc0_conn_rate gt 10 }

Example:

Enable the PROXY protocol for traffic coming from all known proxies.
tcp-request connection expect-proxy layer4 if { src -f proxies.lst }

See  about ACL usage.

See also : “tcp-request session“, ““, “stick-table“

[{if | unless} ]

Perform an action on a new session depending on a layer 4-7 condition

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<action>    defines the action to perform if the condition applies. See
            below.

<condition> is a standard layer 4-7 ACL-based condition (see section 7).

A request's contents can be analyzed at an early stage of request processing
called "TCP content inspection". During this stage, ACL-based rules are
evaluated every time the request contents are updated, until either an
"accept" or a "reject" rule matches, or the TCP request inspection delay
expires with no matching rule.

The first difference between these rules and "" rules
is that "tcp-request content" rules can make use of contents to take a
decision. Most often, these decisions will consider a protocol recognition or
validity. The second difference is that content-based rules can be used in
both frontends and backends. In case of HTTP keep-alive with the client, all
tcp-request content rules are evaluated again, so haproxy keeps a record of
what sticky counters were assigned by a "" versus a
"tcp-request content" rule, and flushes all the content-related ones after
processing an HTTP request, so that they may be evaluated again by the rules
being evaluated again for the next request. This is of particular importance
when the rule tracks some L7 information or when it is conditioned by an
L7-based ACL, since tracking may change between requests.

Content-based rules are evaluated in their exact declaration order. If no
rule matches or if there is no rule, the default action is to accept the
contents. There is no specific limit to the number of rules which may be
inserted.

Several types of actions are supported :
  - accept : the request is accepted
  - do-resolve: perform a DNS resolution
  - reject : the request is rejected and the connection is closed
  - capture : the specified sample expression is captured
  - set-priority-class <expr> | set-priority-offset <expr>
  - { track-sc0 | track-sc1 | track-sc2 } <key> [table <table>]
  - sc-inc-gpc0(<sc-id>)
  - sc-inc-gpc1(<sc-id>)
  - sc-set-gpt0(<sc-id>) <int>
  - set-dst <expr>
  - set-dst-port <expr>
  - set-var(<var-name>) <expr>
  - unset-var(<var-name>)
  - silent-drop
  - send-spoe-group <engine-name> <group-name>
  - use-service <service-name>

They have the same meaning as their counter-parts in ""
so please refer to that section for a complete description.
For "do-resolve" action, please check the "http-request do-resolve"
configuration section.

While there is nothing mandatory about it, it is recommended to use the
track-sc0 in "" rules, track-sc1 for "tcp-request
content" rules in the frontend, and track-sc2 for "tcp-request content"
rules in the backend, because that makes the configuration more readable
and easier to troubleshoot, but this is just a guideline and all counters
may be used everywhere.

Note that the "if/unless" condition is optional. If no condition is set on
the action, it is simply performed unconditionally. That can be useful for
"track-sc*" actions as well as for changing the default action to a reject.

It is perfectly possible to match layer 7 contents with ""
rules, since HTTP-specific ACL matches are able to preliminarily parse the
contents of a buffer before extracting the required data. If the buffered
contents do not parse as a valid HTTP message, then the ACL does not match.
The parser which is involved there is exactly the same as for all other HTTP
processing, so there is no risk of parsing something differently. In an HTTP
backend connected to from an HTTP frontend, it is guaranteed that HTTP
contents will always be immediately present when the rule is evaluated first.

Tracking layer7 information is also possible provided that the information
are present when the rule is processed. The rule processing engine is able to
wait until the inspect delay expires when the data to be tracked is not yet
available.

The "set-dst" and "set-dst-port" are used to set respectively the destination
IP and port. More information on how to use it at "http-request set-dst".

The "set-var" is used to set the content of a variable. The variable is
declared inline. For "" rules, only session-level
variables can be used, without any layer7 contents.

  <var-name> The name of the variable starts with an indication about
             its scope. The scopes allowed are:
               "proc" : the variable is shared with the whole process
               "sess" : the variable is shared with the whole session
               "txn"  : the variable is shared with the transaction
                        (request and response)
               "req"  : the variable is shared only during request
                        processing
               "res"  : the variable is shared only during response
                        processing
             This prefix is followed by a name. The separator is a '.'.
             The name may only contain characters 'a-z', 'A-Z', '0-9',
             '.' and '_'.

  <expr>     Is a standard HAProxy expression formed by a sample-fetch
             followed by some converters.

The "unset-var" is used to unset a variable. See above for details about
<var-name>.

The "set-priority-class" is used to set the queue priority class of the
current request. The value must be a sample expression which converts to an
integer in the range -2047..2047. Results outside this range will be
truncated. The priority class determines the order in which queued requests
are processed. Lower values have higher priority.

The "set-priority-offset" is used to set the queue priority timestamp offset
of the current request. The value must be a sample expression which converts
to an integer in the range -524287..524287. Results outside this range will be
truncated. When a request is queued, it is ordered first by the priority
class, then by the current timestamp adjusted by the given offset in
milliseconds. Lower values have higher priority.
Note that the resulting timestamp is is only tracked with enough precision for
524,287ms (8m44s287ms). If the request is queued long enough to where the
adjusted timestamp exceeds this value, it will be misidentified as highest
priority.  Thus it is important to set "" to a value, where when
combined with the offset, does not exceed this limit.

The "send-spoe-group" is used to trigger sending of a group of SPOE
messages. To do so, the SPOE engine used to send messages must be defined, as
well as the SPOE group to send. Of course, the SPOE engine must refer to an
existing SPOE filter. If not engine name is provided on the SPOE filter line,
the SPOE agent name must be used.

  <engine-name> The SPOE engine name.

  <group-name>  The SPOE group name as specified in the engine configuration.

The "use-service" is used to executes a TCP service which will reply to the
request and stop the evaluation of the rules. This service may choose to
reply by sending any valid response or it may immediately close the
connection without sending anything. Outside natives services, it is possible
to write your own services in Lua. No further "tcp-request" rules are
evaluated.

Example:

tcp-request content use-service lua.deny { src -f /etc/haproxy/blacklist.lst }

Example:

tcp-request content set-var(sess.my_var) src
tcp-request content unset-var(sess.my_var2)

Example:

# Accept HTTP requests containing a Host header saying "example.com"
# and reject everything else.
acl is_host_com hdr(Host) -i example.com
tcp-request inspect-delay 30s
tcp-request content accept if is_host_com
tcp-request content reject

Example:

# reject SMTP connection if client speaks first
tcp-request inspect-delay 30s
acl content_present req_len gt 0
tcp-request content reject if content_present

# Forward HTTPS connection only if client speaks
tcp-request inspect-delay 30s
acl content_present req_len gt 0
tcp-request content accept if content_present
tcp-request content reject

Example:

# Track the last IP(stick-table type string) from X-Forwarded-For
tcp-request inspect-delay 10s
tcp-request content track-sc0 hdr(x-forwarded-for,-1)
# Or track the last IP(stick-table type ip|ipv6) from X-Forwarded-For
tcp-request content track-sc0 req.hdr_ip(x-forwarded-for,-1)

Example:

# track request counts per "base" (concatenation of Host+URL)
tcp-request inspect-delay 10s
tcp-request content track-sc0 base table req-rate

Example:

Track per-frontend and per-backend counters, block abusers at the frontend when the backend detects abuse(and marks gpc0).
frontend http
    # Use General Purpose Counter 0 in SC0 as a global abuse counter
    # protecting all our sites
    stick-table type ip size 1m expire 5m store gpc0
    tcp-request connection track-sc0 src
    tcp-request connection reject if { sc0_get_gpc0 gt 0 }
    ...
    use_backend http_dynamic if { path_end .php }

backend http_dynamic
    # if a source makes too fast requests to this dynamic site (tracked
    # by SC1), block it globally in the frontend.
    stick-table type ip size 1m expire 5m store http_req_rate(10s)
    acl click_too_fast sc1_http_req_rate gt 10
    acl mark_as_abuser sc0_inc_gpc0(http) gt 0
    tcp-request content track-sc1 src
    tcp-request content reject if click_too_fast mark_as_abuser

See  about ACL usage.

See also : “tcp-request connection“, ““, “tcp-request inspect-delay“, and “

• This keyword is available in sections :
• Proxy section

“.

tcp-request inspect-delay

Set the maximum allowed time to wait for data during content inspection

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

People using haproxy primarily as a TCP relay are often worried about the
risk of passing any type of protocol to a server without any analysis. In
order to be able to analyze the request contents, we must first withhold
the data then analyze them. This statement simply enables withholding of
data for at most the specified amount of time.

TCP content inspection applies very early when a connection reaches a
frontend, then very early when the connection is forwarded to a backend. This
means that a connection may experience a first delay in the frontend and a
second delay in the backend if both have tcp-request rules.

Note that when performing content inspection, haproxy will evaluate the whole
rules for every new chunk which gets in, taking into account the fact that
those data are partial. If no rule matches before the aforementioned delay,
a last check is performed upon expiration, this time considering that the
contents are definitive. If no delay is set, haproxy will not wait at all
and will immediately apply a verdict based on the available information.
Obviously this is unlikely to be very useful and might even be racy, so such
setups are not recommended.

As soon as a rule matches, the request is released and continues as usual. If
the timeout is reached and no rule matches, the default policy will be to let
it pass through unaffected.

For most protocols, it is enough to set it to a few seconds, as most clients
send the full request immediately upon connection. Add 3 or more seconds to
cover TCP retransmits but that's all. For some protocols, it may make sense
to use large values, for instance to ensure that the client never talks
before the server (e.g. SMTP), or to wait for a client to talk before passing
data to the server (e.g. SSL). Note that the client timeout must cover at
least the inspection delay, otherwise it will expire first. If the client
closes the connection or if the buffer is full, the delay immediately expires
since the contents will not be able to change anymore.

See also : “tcp-request content accept”, “tcp-request content reject”, ““.

tcp-response content [{if | unless} ]

Perform an action on a session response depending on a layer 4-7 condition

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<action>    defines the action to perform if the condition applies. See
            below.

<condition> is a standard layer 4-7 ACL-based condition (see ).

Response contents can be analyzed at an early stage of response processing
called "TCP content inspection". During this stage, ACL-based rules are
evaluated every time the response contents are updated, until either an
"accept", "close" or a "reject" rule matches, or a TCP response inspection
delay is set and expires with no matching rule.

Most often, these decisions will consider a protocol recognition or validity.

Content-based rules are evaluated in their exact declaration order. If no
rule matches or if there is no rule, the default action is to accept the
contents. There is no specific limit to the number of rules which may be
inserted.

Several types of actions are supported :
  - accept :
      accepts the response if the condition is true (when used with "if")
      or false (when used with "unless"). The first such rule executed ends
      the rules evaluation.

  - close :
      immediately closes the connection with the server if the condition is
      true (when used with "if"), or false (when used with "unless"). The
      first such rule executed ends the rules evaluation. The main purpose of
      this action is to force a connection to be finished between a client
      and a server after an exchange when the application protocol expects
      some long time outs to elapse first. The goal is to eliminate idle
      connections which take significant resources on servers with certain
      protocols.

  - reject :
      rejects the response if the condition is true (when used with "if")
      or false (when used with "unless"). The first such rule executed ends
      the rules evaluation. Rejected session are immediately closed.

  - set-var(<var-name>) <expr>
      Sets a variable.

  - unset-var(<var-name>)
      Unsets a variable.

  - sc-inc-gpc0(<sc-id>):
      This action increments the GPC0 counter according to the sticky
      counter designated by <sc-id>. If an error occurs, this action fails
      silently and the actions evaluation continues.

  - sc-inc-gpc1(<sc-id>):
      This action increments the GPC1 counter according to the sticky
      counter designated by <sc-id>. If an error occurs, this action fails
      silently and the actions evaluation continues.

  - sc-set-gpt0(<sc-id>) <int> :
      This action sets the GPT0 tag according to the sticky counter designated
      by <sc-id> and the value of <int>. The expected result is a boolean. If
      an error occurs, this action silently fails and the actions evaluation
      continues.

  - "silent-drop" :
      This stops the evaluation of the rules and makes the client-facing
      connection suddenly disappear using a system-dependent way that tries
      to prevent the client from being notified. The effect it then that the
      client still sees an established connection while there's none on
      HAProxy. The purpose is to achieve a comparable effect to "tarpit"
      except that it doesn't use any local resource at all on the machine
      running HAProxy. It can resist much higher loads than "tarpit", and
      slow down stronger attackers. It is important to understand the impact
      of using this mechanism. All stateful equipment placed between the
      client and HAProxy (firewalls, proxies, load balancers) will also keep
      the established connection for a long time and may suffer from this
      action. On modern Linux systems running with enough privileges, the
      TCP_REPAIR socket option is used to block the emission of a TCP
      reset. On other systems, the socket's TTL is reduced to 1 so that the
      TCP reset doesn't pass the first router, though it's still delivered to
      local networks. Do not use it unless you fully understand how it works.

  - send-spoe-group <engine-name> <group-name>
      Send a group of SPOE messages.

Note that the "if/unless" condition is optional. If no condition is set on
the action, it is simply performed unconditionally. That can be useful for
for changing the default action to a reject.

It is perfectly possible to match layer 7 contents with "tcp-response
content" rules, but then it is important to ensure that a full response has
been buffered, otherwise no contents will match. In order to achieve this,
the best solution involves detecting the HTTP protocol during the inspection
period.

The "set-var" is used to set the content of a variable. The variable is
declared inline.

  <var-name> The name of the variable starts with an indication about
             its scope. The scopes allowed are:
               "proc" : the variable is shared with the whole process
               "sess" : the variable is shared with the whole session
               "txn"  : the variable is shared with the transaction
                        (request and response)
               "req"  : the variable is shared only during request
                        processing
               "res"  : the variable is shared only during response
                        processing
             This prefix is followed by a name. The separator is a '.'.
             The name may only contain characters 'a-z', 'A-Z', '0-9',
             '.' and '_'.

  <expr>     Is a standard HAProxy expression formed by a sample-fetch
             followed by some converters.

Example:

tcp-request content set-var(sess.my_var) src

The "unset-var" is used to unset a variable. See above for details about
<var-name>.

Example:

tcp-request content unset-var(sess.my_var)

The "send-spoe-group" is used to trigger sending of a group of SPOE
messages. To do so, the SPOE engine used to send messages must be defined, as
well as the SPOE group to send. Of course, the SPOE engine must refer to an
existing SPOE filter. If not engine name is provided on the SPOE filter line,
the SPOE agent name must be used.

  <engine-name> The SPOE engine name.

  <group-name>  The SPOE group name as specified in the engine configuration.

See  about ACL usage.

See also : “tcp-request content“, ““

tcp-request session [{if | unless} ]

Perform an action on a validated session depending on a layer 5 condition

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<action>    defines the action to perform if the condition applies. See
            below.

<condition> is a standard layer5-only ACL-based condition (see ).

Once a session is validated, (i.e. after all handshakes have been completed),
it is possible to evaluate some conditions to decide whether this session
must be accepted or dropped or have its counters tracked. Those conditions
cannot make use of any data contents because no buffers are allocated yet and
the processing cannot wait at this stage. The main use case it to copy some
early information into variables (since variables are accessible in the
session), or to keep track of some information collected after the handshake,
such as SSL-level elements (SNI, ciphers, client cert's CN) or information
from the PROXY protocol header (e.g. track a source forwarded this way). The
extracted information can thus be copied to a variable or tracked using
"track-sc" rules. Of course it is also possible to decide to accept/reject as
with other rulesets. Most operations performed here could also be performed
in "tcp-request content" rules, except that in HTTP these rules are evaluated
for each new request, and that might not always be acceptable. For example a
rule might increment a counter on each evaluation. It would also be possible
that a country is resolved by geolocation from the source IP address,
assigned to a session-wide variable, then the source address rewritten from
an HTTP header for all requests. If some contents need to be inspected in
order to take the decision, the "" statements must be used
instead.

The "tcp-request session" rules are evaluated in their exact declaration
order. If no rule matches or if there is no rule, the default action is to
accept the incoming session. There is no specific limit to the number of
rules which may be inserted.

Several types of actions are supported :
  - accept : the request is accepted
  - reject : the request is rejected and the connection is closed
  - { track-sc0 | track-sc1 | track-sc2 } <key> [table <table>]
  - sc-inc-gpc0(<sc-id>)
  - sc-inc-gpc1(<sc-id>)
  - sc-set-gpt0(<sc-id>) <int>
  - set-var(<var-name>) <expr>
  - unset-var(<var-name>)
  - silent-drop

These actions have the same meaning as their respective counter-parts in
"" and "tcp-request content", so please refer to these
sections for a complete description.

Note that the "if/unless" condition is optional. If no condition is set on
the action, it is simply performed unconditionally. That can be useful for
"track-sc*" actions as well as for changing the default action to a reject.

Example:

Track the original source address by default, or the one advertised in the PROXY protocol header for connection coming from the local proxies. The first connection-level rule enables receipt of the PROXY protocol for these ones, the second rule tracks whatever address we decide to keep after optional decoding.
tcp-request connection expect-proxy layer4 if { src -f proxies.lst }
tcp-request session track-sc0 src

Example:

Accept all sessions from white-listed hosts, reject too fast sessions without counting them, and track accepted sessions. This results in session rate being capped from abusive sources.
tcp-request session accept if { src -f /etc/haproxy/whitelist.lst }
tcp-request session reject if { src_sess_rate gt 10 }
tcp-request session track-sc0 src

Example:

Accept all sessions from white-listed hosts, count all other sessions and reject too fast ones. This results in abusive ones being blocked as long as they don't slow down.
tcp-request session accept if { src -f /etc/haproxy/whitelist.lst }
tcp-request session track-sc0 src
tcp-request session reject if { sc0_sess_rate gt 10 }

See  about ACL usage.

See also : “tcp-request connection“, ““, “stick-table“

Set the maximum allowed time to wait for a response during content inspection

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

See also : “tcp-response content“, ““.

timeout check

Set additional check timeout, but only after a connection has been already
established.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments:

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

If set, haproxy uses min("", "inter") as a connect timeout
for check and "" as an additional read timeout. The "min" is
used so that people running with *very* long "timeout connect" (e.g. those
who needed this due to the queue or tarpit) do not slow down their checks.
(Please also note that there is no valid reason to have such long connect
timeouts, because "" and "timeout tarpit" can always be used to
avoid that).

If "" is not set haproxy uses "inter" for complete check
timeout (connect + read) exactly like all <1.3.15 version.

In most cases check request is much simpler and faster to handle than normal
requests and people may want to kick out laggy servers so this timeout should
be smaller than "".

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it.

See also: “timeout connect“, ““, “timeout server“, ““.

timeout client

(deprecated)

Set the maximum inactivity time on the client side.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the client is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase, when the client sends the request, and during the
response while it is reading data sent by the server. That said, for the
first phase, it is preferable to set the "timeout http-request" to better
protect HAProxy from Slowloris like attacks. The value is specified in
milliseconds by default, but can be in any other unit if the number is
suffixed by the unit, as specified at the top of this document. In TCP mode
(and to a lesser extent, in HTTP mode), it is highly recommended that the
client timeout remains equal to the server timeout in order to avoid complex
situations to debug. It is a good practice to cover one or several TCP packet
losses by specifying timeouts that are slightly above multiples of 3 seconds
(e.g. 4 or 5 seconds). If some long-lived sessions are mixed with short-lived
sessions (e.g. WebSocket and HTTP), it's worth considering "",
which overrides "timeout client" and "" for tunnels, as well as
"timeout client-fin" for half-closed connections.

This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may result in accumulation of expired sessions in
the system if the system's timeouts are not configured either.

This also applies to HTTP/2 connections, which will be closed with GOAWAY.

This parameter replaces the old, deprecated "". It is recommended
to use it to write new configurations. The form "timeout clitimeout" is
provided only by backwards compatibility but its use is strongly discouraged.

See also : ““, “timeout server“, ““, “timeout http-request“.

Set the inactivity timeout on the client side for half-closed connections.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the client is expected to acknowledge or
send data while one direction is already shut down. This timeout is different
from "timeout client" in that it only applies to connections which are closed
in one direction. This is particularly useful to avoid keeping connections in
FIN_WAIT state for too long when clients do not disconnect cleanly. This
problem is particularly common long connections such as RDP or WebSocket.
Note that this timeout can override "" when a connection shuts
down in one direction. It is applied to idle HTTP/2 connections once a GOAWAY
frame was sent, often indicating an expectation that the connection quickly
ends.

This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. By default it is not set, so half-closed connections
will use the other timeouts (timeout.client or timeout.tunnel).

See also : “timeout client“, ““, and “timeout tunnel“.

timeout contimeout (deprecated)

Set the maximum time to wait for a connection attempt to a server to succeed.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

If the server is located on the same LAN as haproxy, the connection should be
immediate (less than a few milliseconds). Anyway, it is a good practice to
cover one or several TCP packet losses by specifying timeouts that are
slightly above multiples of 3 seconds (e.g. 4 or 5 seconds). By default, the
connect timeout also presets both queue and tarpit timeouts to the same value
if these have not been specified.

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may result in accumulation of failed sessions in
the system if the system's timeouts are not configured either.

This parameter replaces the old, deprecated "". It is recommended
to use it to write new configurations. The form "timeout contimeout" is
provided only by backwards compatibility but its use is strongly discouraged.

See also: ““, “timeout queue“, ““, “contimeout“, ““.

timeout http-keep-alive

Set the maximum allowed time to wait for a new HTTP request to appear

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

By default, the time to wait for a new request in case of keep-alive is set
by "". However this is not always convenient because some
people want very short keep-alive timeouts in order to release connections
faster, and others prefer to have larger ones but still have short timeouts
once the request has started to present itself.

The "http-keep-alive" timeout covers these needs. It will define how long to
wait for a new HTTP request to start coming after a response was sent. Once
the first byte of request has been seen, the "
This keyword is available in sections :
Proxy section
" timeout is used
to wait for the complete request to come. Note that empty lines prior to a
new request do not refresh the timeout and are not counted as a new request.

There is also another difference between the two timeouts : when a connection
expires during timeout http-keep-alive, no error is returned, the connection
just closes. If the connection expires in "http-request
This keyword is available in sections :
Alphabetically sorted keywords reference
" while waiting for a
connection to complete, a HTTP 408 error is returned.

In general it is optimal to set this value to a few tens to hundreds of
milliseconds, to allow users to fetch all objects of a page at once but
without waiting for further clicks. Also, if set to a very small value (e.g.
1 millisecond) it will probably only accept pipelined requests but not the
non-pipelined ones. It may be a nice trade-off for very large sites running
with tens to hundreds of thousands of clients.

If this parameter is not set, the "
This keyword is available in sections :
Proxy section
" timeout applies, and if both
are not set, "timeout client" still applies at the lower level. It should be
set in the frontend to take effect, unless the frontend is in TCP mode, in
which case the HTTP backend's timeout will be used.

When using HTTP/2 "" is applied instead. This is so we can keep
using short keep-alive timeouts in HTTP/1.1 while using longer ones in HTTP/2
(where we only have one connection per client and a connection setup).

See also : “timeout http-request“, ““.

timeout http-request

Set the maximum allowed time to wait for a complete HTTP request

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

In order to offer DoS protection, it may be required to lower the maximum
accepted time to receive a complete HTTP request without affecting the client
timeout. This helps protecting against established connections on which
nothing is sent. The client timeout cannot offer a good protection against
this abuse because it is an inactivity timeout, which means that if the
attacker sends one character every now and then, the timeout will not
trigger. With the HTTP request timeout, no matter what speed the client
types, the request will be aborted if it does not complete in time. When the
timeout expires, an HTTP 408 response is sent to the client to inform it
about the problem, and the connection is closed. The logs will report
termination codes "cR". Some recent browsers are having problems with this
standard, well-documented behavior, so it might be needed to hide the 408
code using "" or "errorfile 408 /dev/null". See
more details in the explanations of the "cR" termination code in section 8.5.

By default, this timeout only applies to the header part of the request,
and not to any data. As soon as the empty line is received, this timeout is
not used anymore. When combined with "", this
timeout also applies to the body of the request..
It is used again on keep-alive connections to wait for a second
request if "timeout http-keep-alive" is not set.

Generally it is enough to set it to a few seconds, as most clients send the
full request immediately upon connection. Add 3 or more seconds to cover TCP
retransmits but that's all. Setting it to very low values (e.g. 50 ms) will
generally work on local networks as long as there are no packet losses. This
will prevent people from sending bare HTTP requests using telnet.

If this parameter is not set, the client timeout still applies between each
chunk of the incoming request. It should be set in the frontend to take
effect, unless the frontend is in TCP mode, in which case the HTTP backend's
timeout will be used.

See also : ““, “http-ignore-probes“, ““, and “timeout client“, ““.

timeout queue

Set the maximum time to wait in the queue for a connection slot to be free

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

When a server's maxconn is reached, connections are left pending in a queue
which may be server-specific or global to the backend. In order not to wait
indefinitely, a timeout is applied to requests pending in the queue. If the
timeout is reached, it is considered that the request will almost never be
served, so it is dropped and a 503 error is returned to the client.

The "" statement allows to fix the maximum time for a request to
be left pending in a queue. If unspecified, the same value as the backend's
connection timeout ("timeout connect") is used, for backwards compatibility
with older versions with no "" parameter.

See also : “timeout connect“, ““.

timeout server

(deprecated)

Set the maximum inactivity time on the server side.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the server is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase of the server's response, when it has to send the
headers, as it directly represents the server's processing time for the
request. To find out what value to put there, it's often good to start with
what would be considered as unacceptable response times, then check the logs
to observe the response time distribution, and adjust the value accordingly.

The value is specified in milliseconds by default, but can be in any other
unit if the number is suffixed by the unit, as specified at the top of this
document. In TCP mode (and to a lesser extent, in HTTP mode), it is highly
recommended that the client timeout remains equal to the server timeout in
order to avoid complex situations to debug. Whatever the expected server
response times, it is a good practice to cover at least one or several TCP
packet losses by specifying timeouts that are slightly above multiples of 3
seconds (e.g. 4 or 5 seconds minimum). If some long-lived sessions are mixed
with short-lived sessions (e.g. WebSocket and HTTP), it's worth considering
"timeout tunnel", which overrides "" and "timeout server" for
tunnels.

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may result in accumulation of expired sessions in
the system if the system's timeouts are not configured either.

This parameter replaces the old, deprecated "". It is recommended
to use it to write new configurations. The form "timeout srvtimeout" is
provided only by backwards compatibility but its use is strongly discouraged.

See also : ““, “timeout client“ and ““.

timeout server-fin

Set the inactivity timeout on the server side for half-closed connections.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the server is expected to acknowledge or
send data while one direction is already shut down. This timeout is different
from "" in that it only applies to connections which are closed
in one direction. This is particularly useful to avoid keeping connections in
FIN_WAIT state for too long when a remote server does not disconnect cleanly.
This problem is particularly common long connections such as RDP or WebSocket.
Note that this timeout can override "timeout tunnel" when a connection shuts
down in one direction. This setting was provided for completeness, but in most
situations, it should not be needed.

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. By default it is not set, so half-closed connections
will use the other timeouts (timeout.server or timeout.tunnel).

See also : ““, “timeout server“, and ““.

timeout tarpit

Set the duration for which tarpitted connections will be maintained

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

Arguments :

<timeout> is the tarpit duration specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

When a connection is tarpitted using "" or
"reqtarpit", it is maintained open with no activity for a certain
amount of time, then closed. "" defines how long it will
be maintained open.

The value is specified in milliseconds by default, but can be in any other
unit if the number is suffixed by the unit, as specified at the top of this
document. If unspecified, the same value as the backend's connection timeout
("timeout connect") is used, for backwards compatibility with older versions
with no "" parameter.

See also : “timeout connect“, ““.

timeout tunnel

Set the maximum inactivity time on the client and server side for tunnels.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments :

<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The tunnel timeout applies when a bidirectional connection is established
between a client and a server, and the connection remains inactive in both
directions. This timeout supersedes both the client and server timeouts once
the connection becomes a tunnel. In TCP, this timeout is used as soon as no
analyzer remains attached to either connection (e.g. tcp content rules are
accepted). In HTTP, this timeout is used when a connection is upgraded (e.g.
when switching to the WebSocket protocol, or forwarding a CONNECT request
to a proxy), or after the first response when no keepalive/close option is
specified.

Since this timeout is usually used in conjunction with long-lived connections,
it usually is a good idea to also set "" to handle the
situation where a client suddenly disappears from the net and does not
acknowledge a close, or sends a shutdown and does not acknowledge pending
data anymore. This can happen in lossy networks where firewalls are present,
and is detected by the presence of large amounts of sessions in a FIN_WAIT
state.

The value is specified in milliseconds by default, but can be in any other
unit if the number is suffixed by the unit, as specified at the top of this
document. Whatever the expected normal idle time, it is a good practice to
cover at least one or several TCP packet losses by specifying timeouts that
are slightly above multiples of 3 seconds (e.g. 4 or 5 seconds minimum).

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it.

Example :

defaults http
    option http-server-close
    timeout connect 5s
    timeout client 30s
    timeout client-fin 30s
    timeout server 30s
    timeout tunnel  1h    # timeout to use with WebSocket and CONNECT

See also : “timeout client“, ““, “timeout server“.

(deprecated)

Enable client-side transparent proxying

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

Arguments : none

This keyword was introduced in order to provide layer 7 persistence to layer
3 load balancers. The idea is to use the OS's ability to redirect an incoming
connection for a remote address to a local process (here HAProxy), and let
this process know what address was initially requested. When this option is
used, sessions without cookies will be forwarded to the original destination
IP address of the incoming request (which should match that of another
equipment), while requests with cookies will still be forwarded to the
appropriate server.

The "transparent" keyword is deprecated, use "" instead.

Note that contrary to a common belief, this option does NOT make HAProxy
present the client's IP to the server when establishing the connection.

See also: “option transparent“

Generate a unique ID for each request.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<string>   is a log-format string.

This keyword creates a ID for each request using the custom log format. A
unique ID is useful to trace a request passing through many components of
a complex infrastructure. The newly created ID may also be logged using the
%ID tag the log-format string.

The format should be composed from elements that are guaranteed to be
unique when combined together. For instance, if multiple haproxy instances
are involved, it might be important to include the node name. It is often
needed to log the incoming connection's source and destination addresses
and ports. Note that since multiple requests may be performed over the same
connection, including a request counter may help differentiate them.
Similarly, a timestamp may protect against a rollover of the counter.
Logging the process ID will avoid collisions after a service restart.

It is recommended to use hexadecimal notation for many fields since it
makes them more compact and saves space in logs.

Example:

unique-id-format %{+X}o\ %ci:%cp_%fi:%fp_%Ts_%rt:%pid

will generate:

       7F000001:8296_7F00001E:1F90_4F7B0A69_0003:790A

See also: “unique-id-header“

Add a unique ID header in the HTTP request.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

Arguments :

<name>   is the name of the header.

Add a unique-id header in the HTTP request sent to the server, using the
unique-id-format. It can't work if the unique-id-format doesn't exist.

Example:

use_backend [{if | unless} ]

Switch to a specific backend if/unless an ACL-based condition is matched.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

Arguments :

<backend>   is the name of a valid backend or "listen" section, or a
            "" string resolving to a backend name.

<condition> is a condition composed of ACLs, as described in section 7. If
            it is omitted, the rule is unconditionally applied.

When doing content-switching, connections arrive on a frontend and are then
dispatched to various backends depending on a number of conditions. The
relation between the conditions and the backends is described with the
"" keyword. While it is normally used with HTTP processing, it can
also be used in pure TCP, either without content using stateless ACLs (e.g.
source address validation) or combined with a "tcp-request" rule to wait for
some payload.

There may be as many "" rules as desired. All of these rules are
evaluated in their declaration order, and the first one which matches will
assign the backend.

In the first form, the backend will be used if the condition is met. In the
second form, the backend will be used if the condition is not met. If no
condition is valid, the backend defined with "default_backend" will be used.
If no default backend is defined, either the servers in the same section are
used (in case of a "listen" section) or, in case of a frontend, no server is
used and a 503 service unavailable response is returned.

Note that it is possible to switch from a TCP frontend to an HTTP backend. In
this case, either the frontend has already checked that the protocol is HTTP,
and backend processing will immediately follow, or the backend will wait for
a complete HTTP request to get in. This feature is useful when a frontend
must decode several protocols on a unique port, one of them being HTTP.

When <backend> is a simple name, it is resolved at configuration time, and an
error is reported if the specified backend does not exist. If <backend> is
a log-format string instead, no check may be done at configuration time, so
the backend name is resolved dynamically at run time. If the resulting
backend name does not correspond to any valid backend, no other rule is
evaluated, and the default_backend directive is applied instead. Note that
when using dynamic backend names, it is highly recommended to use a prefix
that no other backend uses in order to ensure that an unauthorized backend
cannot be forced from the request.

It is worth mentioning that "" rules with an explicit name are
used to detect the association between frontends and backends to compute the
backend's "fullconn" setting. This cannot be done for dynamic names.

See also: ““, “tcp-request“, ““, “log-format“, and about ACLs.

use-server if

unless

Only use a specific server if/unless an ACL-based condition is matched.

May be used in sections :

Arguments :

<server>    is the name of a valid server in the same backend section.

<condition> is a condition composed of ACLs, as described in section 7.

By default, connections which arrive to a backend are load-balanced across
the available servers according to the configured algorithm, unless a
persistence mechanism such as a cookie is used and found in the request.

Sometimes it is desirable to forward a particular request to a specific
server without having to declare a dedicated backend for this server. This
can be achieved using the "" rules. These rules are evaluated after
the "redirect" rules and before evaluating cookies, and they have precedence
on them. There may be as many "" rules as desired. All of these
rules are evaluated in their declaration order, and the first one which
matches will assign the server.

If a rule designates a server which is down, and "option persist" is not used
and no force-persist rule was validated, it is ignored and evaluation goes on
with the next rules until one matches.

In the first form, the server will be used if the condition is met. In the
second form, the server will be used if the condition is not met. If no
condition is valid, the processing continues and the server will be assigned
according to other persistence mechanisms.

Note that even if a rule is matched, cookie processing is still performed but
does not assign the server. This allows prefixed cookies to have their prefix
stripped.

The "" statement works both in HTTP and TCP mode. This makes it
suitable for use with content-based inspection. For instance, a server could
be selected in a farm according to the TLS SNI field. And if these servers
have their weight set to zero, they will not be used for other traffic.

Example :