Cache Filter

    All incoming requests are routed via the front Envoy, which acts as a reverse proxy sitting on the edge of the network. Ports 8000 and 8001 are exposed by docker compose (see /examples/cache/docker-compose.yaml) to handle HTTP calls to the services, and requests to /admin respectively. Two backend services are deployed behind the front Envoy, each with a sidecar Envoy.

    The front Envoy is configured to run the Cache Filter, which stores cacheable responses in an in-memory cache, and serves it to subsequent requests. In this demo, the responses that are served by the deployed services are stored in . This file is mounted to both services’ containers, so any changes made to the stored responses while the services are running should be instantly effective (no need to rebuild or rerun).

    For the purposes of the demo, a response’s date of creation is appended to its body before being served. An Etag is computed for every response for validation purposes, which only depends on the response body in the yaml file (i.e. the appended date is not taken into account). Cached responses can be identified by having an age header. Validated responses can be identified by having a generation date older than the date header; as when a response is validated the date header is updated, while the body stays the same. Validated responses do not have an age header. Responses served from the backend service have no age header, and their date header is the same as their generation date.

    The following documentation runs through the setup of Envoy described above.

    Ensure that you have a recent versions of docker and docker-compose installed.

    A simple way to achieve this is via the Docker Desktop.

    If you have not cloned the Envoy repo, clone it with:

    SSH

    HTTPS

    1. git clone https://github.com/envoyproxy/envoy.git
    1. $ pwd
    2. envoy/examples/cache
    3. $ docker-compose build --pull
    4. $ docker-compose up -d
    5. $ docker-compose ps
    7.        Name                      Command            State                             Ports
    8. ------------------------------------------------------------------------------------------------------------------------
    9. cache_front-envoy_1   /docker-entrypoint.sh /bin ... Up      10000/tcp, 0.0.0.0:8000->8000/tcp, 0.0.0.0:8001->8001/tcp
    10. cache_service1_1      /bin/sh -c /usr/local/bin/ ... Up      10000/tcp, 8000/tcp
    11. cache_service2_1      /bin/sh -c /usr/local/bin/ ... Up      10000/tcp, 8000/tcp

    You can now send a request to both services via the front-envoy. Note that since the two services have different routes, identical requests to different services have different cache entries (i.e. a request sent to service 2 will not be served by a cached response produced by service 1).

    curl -i localhost:8000/service/<service_no>/<response>

    service_no: The service to send the request to, 1 or 2.

    response: The response that is being requested. The responses are found in .

    The provided example responses are:

    • valid-for-minute

      This response remains fresh in the cache for a minute. After which, the response gets validated by the backend service before being served from the cache. If found to be updated, the new response is served (and cached). Otherwise, the cached response is served and refreshed.

    • private

      This response is private; it cannot be stored by shared caches (such as proxies). It will always be served from the backend service.

    • This response has to be validated every time before being served.

    Example responses

    1. valid-for-minute

    Naturally, response date header is the same time as the generated time. Sending the same request after 30 seconds gives the same exact response with the same generation date, but with an age header as it was served from cache:

    1. HTTP/1.1 200 OK
    2. content-type: text/html; charset=utf-8
    3. content-length: 103
    4. cache-control: max-age=60
    5. custom-header: any value
    6. etag: "172ae25df822c3299cf2248694b4ce23"
    7. date: Fri, 11 Sep 2020 03:20:40 GMT
    8. server: envoy
    9. x-envoy-upstream-service-time: 11
    10. age: 30
    12. This response will stay fresh for one minute
    13. Response body generated at: Fri, 11 Sep 2020 03:20:40 GMT

    After 1 minute and 1 second:

    1. $ curl -i localhost:8000/service/1/valid-for-minute
    2. HTTP/1.1 200 OK
    3. cache-control: max-age=60
    4. custom-header: any value
    5. etag: "172ae25df822c3299cf2248694b4ce23"
    6. date: Fri, 11 Sep 2020 03:21:41 GMT
    7. server: envoy
    8. x-envoy-upstream-service-time: 8
    9. content-length: 103
    10. content-type: text/html; charset=utf-8
    12. Response body generated at: Fri, 11 Sep 2020 03:20:40 GMT

    The same response was served after being validated with the backend service. You can verify this as the response generation time is the same, but the response date header was updated with the validation response date. Also, no header.

    Every time the response is validated, it stays fresh for another minute. If the response body changes while the cached response is still fresh, the cached response will still be served. The cached response will only be updated when it is no longer fresh.

    2. private

    No matter how many times you make this request, you will always receive a new response; new date of generation, new date header, and no age header.

    3. no-cache
    1. $ curl -i localhost:8000/service/1/no-cache
    2. HTTP/1.1 200 OK
    3. content-type: text/html; charset=utf-8
    4. content-length: 130
    5. cache-control: max-age=0, no-cache
    6. etag: "ce39a53bd6bb8abdb2488a5a375397e4"
    7. date: Fri, 11 Sep 2020 03:23:07 GMT
    8. server: envoy
    9. x-envoy-upstream-service-time: 7
    11. This response can be cached, but it has to be validated on each request
    12. Response body generated at: Fri, 11 Sep 2020 03:23:07 GMT

    After a few seconds:

    1. $ curl -i localhost:8000/service/1/no-cache
    2. HTTP/1.1 200 OK
    3. cache-control: max-age=0, no-cache
    4. etag: "ce39a53bd6bb8abdb2488a5a375397e4"
    5. date: Fri, 11 Sep 2020 03:23:12 GMT
    6. server: envoy
    7. x-envoy-upstream-service-time: 7
    8. content-length: 130
    9. content-type: text/html; charset=utf-8
    11. This response can be cached, but it has to be validated on each request

    You will receive a cached response that has the same generation time. However, the date header will always be updated as this response will always be validated first. Also, no age header.

    If you change the response body in the yaml file:

    You will receive a new response that’s served from the backend service. The new response will be cached for subsequent requests.

    You can also add new responses to the yaml file with different cache-control headers and start experimenting! To learn more about caching and cache-control headers visit the MDN Web Docs.