Pulsar Functions overview

    • consume messages from one or more Pulsar topics,
    • apply a user-supplied processing logic to each message,
    • publish the results of the computation to another topic.The following is an example of a Pulsar Function written in Java (using the native interface).

    The following is an example of a Pulsar Function written in Python (using the ).

    2.     return "{0}!".format(input)

    The following is an example of a Pulsar Function written in Go.

    1. import (
    2.     "fmt"
    3.     "context"
    5.     "github.com/apache/pulsar/pulsar-function-go/pf"
    6. )
    8. func HandleRequest(ctx context.Context, in []byte) error {
    9.     fmt.Println(string(in) + "!")
    10.     return nil
    11. }
    13. func main() {
    14.     pf.Start(HandleRequest)
    15. }

    A Pulsar Function is executed each time a message is published to its input topic. For example, if a function has an input topic called tweet-stream, the function runs each time a message is published to tweet-stream.

    With Pulsar Functions, you can create complex processing logic without deploying a separate neighboring system (such as Apache Storm, , Apache Flink). Pulsar Functions are computing infrastructure of Pulsar messaging system. The core goal is tied to a series of other goals:

    • Developer productivity ( vs Pulsar Functions SDK functions)
    • Easy troubleshooting
    • Operational simplicity (no need for an external processing system)

    Inspirations

    Pulsar Functions are inspired by (and take cues from) several systems and paradigms:

    • Stream processing engines such as Apache Storm, , and Apache Flink

    • "Serverless" and "Function as a Service" (FaaS) cloud platforms like , Google Cloud Functions, and Pulsar Functions can be described as

    • Lambda-style functions that are

    • specifically designed to use Pulsar as a message bus.

    Programming model

    The core programming model of Pulsar Functions is simple. Functions receive messages from one or more input topics. Each time a message is received, the function will complete the following tasks.

    • Apply some processing logic to the input and write output to:
      • An output topic in Pulsar
    • Write logs to a log topic (potentially for debugging purposes)
    • Increment a counter

    If you implement the classic word count example using Pulsar Functions, it looks something like this:

    Pulsar Functions word count example

    To write the function in with Pulsar Functions SDK for Java, you can write the function as follows.

    1. package org.example.functions;
    3. import org.apache.pulsar.functions.api.Context;
    4. import org.apache.pulsar.functions.api.Function;
    6. import java.util.Arrays;
    8. public class WordCountFunction implements Function<String, Void> {
    9.     // This function is invoked every time a message is published to the input topic
    10.     @Override
    11.     public Void process(String input, Context context) throws Exception {
    12.         Arrays.asList(input.split(" ")).forEach(word -> {
    13.             String counterKey = word.toLowerCase();
    14.             context.incrCounter(counterKey, 1);
    15.         });
    16.         return null;
    17.     }
    18. }

    Bundle and build the JAR file to be deployed. You can find approaches in and Creating a NAR package.Then in your Pulsar cluster using the command line as follows.

    1. $ bin/pulsar-admin functions create \
    2.   --jar target/my-jar-with-dependencies.jar \
    3.   --classname org.example.functions.WordCountFunction \
    4.   --tenant public \
    5.   --name word-count \
    6.   --inputs persistent://public/default/sentences \
    7.   --output persistent://public/default/count

    Content-based routing example

    Pulsar Functions are used in many cases. The following is a sophisticated example that involves content-based routing.

    For example, a function takes items (strings) as input and publishes them to either a fruits or vegetables topic, depending on the item. Or, if an item is neither fruit nor vegetable, a warning is logged to a log topic. The following is a visual representation.

    If you implement this routing functionality in Python, it looks something like this:

    1. from pulsar import Function
    3. class RoutingFunction(Function):
    4.     def __init__(self):
    5.         self.fruits_topic = "persistent://public/default/fruits"
    6.         self.vegetables_topic = "persistent://public/default/vegetables"
    8.     def is_fruit(item):
    9.         return item in ["apple", "orange", "pear", "other fruits..."]
    11.     def is_vegetable(item):
    12.         return item in ["carrot", "lettuce", "radish", "other vegetables..."]
    14.     def process(self, item, context):
    15.         if self.is_fruit(item):
    16.             context.publish(self.fruits_topic, item)
    17.         elif self.is_vegetable(item):
    18.             context.publish(self.vegetables_topic, item)
    19.         else:
    20.             warning = "The item {0} is neither a fruit nor a vegetable".format(item)
    21.             context.get_logger().warn(warning)

    Command-line interface

    Pulsar Functions are managed using the pulsar-admin CLI tool (in particular the command). The following example runs a function in the local run mode.

    1. $ bin/pulsar-admin functions localrun \
    3.   --output persistent://public/default/test_result \
    4.   --jar examples/api-examples.jar \
    5.   --classname org.apache.pulsar.functions.api.examples.ExclamationFunction

    Each Pulsar Function has a Fully Qualified Function Name (FQFN) that consists of three elements: the function tenant, namespace, and function name. FQFN looks like this:

    1. tenant/namespace/name

    Configuration

    You can configure a Pulsar Function in the following ways:

    • Via command-line arguments passed to the interface
    • Via YAML configuration filesIf you use a YAML configuration file, you must specify a path to the file on the command line. The following is an example.

    The following is an example of the my-function.yaml file.

    1. name: my-function
    2. tenant: public
    3. namespace: default
    4. jar: ./target/my-functions.jar
    5. className: org.example.pulsar.functions.MyFunction
    6. inputs:
    7. - persistent://public/default/test_src
    8. output: persistent://public/default/test_result

    You can specify some function attributes via CLI arguments or in a configuration file in YAML format.

    Supported languages

    Currently, you can write Pulsar Functions in Java, , and Go. Support for additional languages is coming soon.

    Pulsar Functions API

    Pulsar Functions API enables you to create processing logic that is:

    • Type safe. Pulsar Functions can process raw bytes or more complex, application-specific types.
    • Based on SerDe (Serialization/Deserialization). A variety of types are supported "out of the box" but you can also create your own custom SerDe logic.

    Function context

    Each Pulsar Function created using has access to a context object that both provides:

    • A wide variety of information about the function, including:
    • The name of the function
    • The tenant and namespace of the function
    • User-supplied configuration values
    • Special functionality, including:
    • The ability to produce to a specified logging topic
    • The ability to produce metrics

    Language-native functions

    "Native" functions are supported in Java and Python, which means a Pulsar Function can have no dependencies.

    The benefit of native functions is that they do not have any dependencies beyond what's already available in Java/Python "out of the box." The downside is that they do not provide access to the function context, which is necessary for a variety of functionalities, including , user configuration, and more.

    To enable a Pulsar Function to access to a , you can use Pulsar Functions SDK, available for Java, , and Go.

    The following is a Java function example that uses information about its context.

    1. import org.apache.pulsar.functions.api.Context;
    2. import org.apache.pulsar.functions.api.Function;
    3. import org.slf4j.Logger;
    5. public class ContextAwareFunction implements Function<String, Void> {
    6.     @Override
    7.     public Void process(String input, Context, context) {
    8.         Logger LOG = context.getLogger();
    9.         String functionTenant = context.getTenant();
    10.         String functionNamespace = context.getNamespace();
    11.         String functionName = context.getFunctionName();
    12.         LOG.info("Function tenant/namespace/name: {}/{}/{}", functionTenant, functionNamespace, functionName);
    13.         return null;
    14.     }
    15. }

    Python

    The following is a Python function example that uses information about its context.

    1. from pulsar import Function
    3. class ContextAwareFunction(Function):
    4.     def process(self, input, context):
    5.         log = context.get_logger()
    6.         function_tenant = context.get_function_tenant()
    7.         function_namespace = context.get_function_namespace()
    8.         function_name = context.get_function_name()
    9.         log.info("Function tenant/namespace/name: {0}/{1}/{2}".format(function_tenant, function_namespace, function_name))

    Go

    The following is a Go function example that uses information about its context.

    1. import (
    2.     "context"
    3.     "fmt"
    5.     "github.com/apache/pulsar/pulsar-function-go/log"
    6.     "github.com/apache/pulsar/pulsar-function-go/pf"
    7. )
    9.     if fc, ok := pf.FromContext(ctx); ok {
    10.         tenant := fc.GetFuncTenant()
    11.         namespace := fc.GetFuncNamespace()
    12.         name := fc.GetFuncName()
    13.         log.Info("Function tenant/namespace/name: %s/%s/%s\n", tenant, namespace, name)
    14.     }
    15. }
    17. func main() {
    18.     pf.Start(contextFunc)
    19. }

    Deployment

    Pulsar Functions support a variety of deployment options. You can deploy a Pulsar Function in the following ways.

    Local run mode

    If you run a Pulsar Function in the local run mode, you run it on the machine where you run commands(for example, your laptop, an instance). The following example is about the localrun command.

    1. $ bin/pulsar-admin functions localrun \
    2.   --py myfunc.py \
    3.   --classname myfunc.SomeFunction \
    4.   --inputs persistent://public/default/input-1 \
    5.   --output persistent://public/default/output-1

    By default, the function connects to a Pulsar cluster running on the same machine, via a local broker service URL of pulsar://localhost:6650. If you run a function with the local run mode, and connect it to a non-local Pulsar cluster, specify a different broker URL using the —brokerServiceUrl flag. The following is an example.

    1. $ bin/pulsar-admin functions localrun \
    2.   --broker-service-url pulsar://my-cluster-host:6650 \
    3.   # Other function parameters

    When you run Pulsar Functions in the cluster mode, the function code is uploaded to a Pulsar broker and runs alongside the broker rather than in your . You can run a function in the cluster mode using the command. The following is an example.

    1. $ bin/pulsar-admin functions create \
    2.   --py myfunc.py \
    3.   --classname myfunc.SomeFunction \
    4.   --inputs persistent://public/default/input-1 \
    5.   --output persistent://public/default/output-1

    This command uploads myfunc.py to Pulsar, which uses the code to start one instances of the function.

    Run instances in parallel

    When you create Pulsar Functions and run in the , only one instance of Pulsar Functions is running by default. However, you can run multiple instances in parallel. Specify the number of instances when you create Pulsar Functions, or update an existing single-instance function with a new parallel factor.

    Function instance resources

    When you run Pulsar Functions in the , you can specify the resources that are assigned to each function instance.

    The following example allocates 8 cores, 8 GB of RAM, and 10 GB of disk space to a function.

    1. $ bin/pulsar-admin functions create \
    2.   --jar target/my-functions.jar \
    3.   --classname org.example.functions.MyFunction \
    4.   --cpu 8 \
    5.   --ram 8589934592 \
    6.   --disk 10737418240

    For more information on resources, see the documentation.

    Logging

    Pulsar Functions created using can send logs to a log topic that you specify as part of the function configuration. The function created using the following command produces all logs on the persistent://public/default/my-func-1-log topic.

    1. $ bin/pulsar-admin functions create \
    2.   --name my-func-1 \
    3.   --log-topic persistent://public/default/my-func-1-log \
    4.   # Other configs

    The following is an example of Java function that logs at different log levels based on the function input.

    1. public class LoggerFunction implements Function<String, Void> {
    2.     @Override
    3.     public Void process(String input, Context context) {
    4.         Logger LOG = context.getLogger();
    5.         if (input.length() <= 100) {
    6.             LOG.info("This string has a length of {}", input);
    7.         } else {
    8.             LOG.warn("This string is getting too long! It has {} characters", input);
    9.         }
    10.     }
    11. }

    The following is an example of that logs at different log levels based on the function input.

    1. import (
    2.     "context"
    4.     "github.com/apache/pulsar/pulsar-function-go/log"
    5.     "github.com/apache/pulsar/pulsar-function-go/pf"
    6. )
    8. func loggerFunc(ctx context.Context, input []byte) {
    9.     if len(input) <= 100 {
    10.         log.Infof("This input has a length of: %d", len(input))
    11.     } else {
    12.         log.Warnf("This input is getting too long! It has {%d} characters", len(input))
    13.     }
    14. }
    16. func main() {
    17.     pf.Start(loggerFunc)
    18. }

    When you use logTopic related functionalities in Go Function, import github.com/apache/pulsar/pulsar-function-go/log, and you do not have to use the getLogger() context object. The approach is different from Java Function and Python Function.

    You can pass arbitrary key-values to Pulsar Functions via the command line (both keys and values must be string). This set of key-values is called the functions user configuration. User configuration must consist of JSON strings.

    The following example passes user configuration to a function.

    1. $ bin/pulsar-admin functions create \
    2.   --user-config '{"key-1":"value-1","key-2","value-2"}' \
    3.   # Other configs

    The following example accesses that configuration map.

    1. public class ConfigMapFunction implements Function<String, Void> {
    2.     @Override
    3.     public Void process(String input, Context context) {
    4.         String val1 = context.getUserConfigValue("key1").get();
    5.         String val2 = context.getUserConfigValue("key2").get();
    6.         context.getLogger().info("The user-supplied values are {} and {}", val1, val2);
    7.         return null;
    8.     }
    9. }

    Trigger Pulsar Functions

    You can a Pulsar Function running in the cluster mode with the . When triggering a Pulsar Function, you can pass a specific value to the Function and get the return value without creating a client. Triggering is useful for, but not limited to, testing and debugging purposes.

    The following is an example of Pulsar Functions written in Python (using the native interface) that simply reverses string inputs.

    1. def process(input):
    2.     return input[::-1]

    If the function is running in a Pulsar cluster, you can trigger it with the following commands.

    And then welcome to Pulsar Functions is displayed in the console output.

    NoteInstead of passing a string via the CLI, you can trigger Pulsar Functions with the contents of a file using the —triggerFile flag.

    Processing guarantees

    Pulsar Functions provide three different messaging semantics that you can apply to any function.

    This command, for example, runs a function in the cluster mode with effectively-once guarantees applied.

    1. $ bin/pulsar-admin functions create \
    2.   --name my-effectively-once-function \
    3.   --processing-guarantees EFFECTIVELY_ONCE \

    Metrics

    Pulsar Functions use Apache BookKeeper as a state storage interface. Pulsar installation, including the local standalone installation, includes deployment of BookKeeper bookies.