Kafka Streams examples

This sub-folder contains code examples that demonstrate how to implement real-time processing applications using Kafka Streams, which is a new stream processing library included with the Apache Kafka open source project.

Table of Contents

• Available examples
  • Java
  • Scala
• Requirements
  • Apache Kafka
  • Confluent Platform
  • Java
  • Scala
• Packaging and running the examples
• Development
• Version Compatibility Matrix

Available examples

This repository has several branches to help you find the correct code examples for the version of Apache Kafka and/or Confluent Platform that you are using. See Version Compatibility Matrix below for details.

There are two kinds of examples:

• Examples under src/main/: These examples are short and concise. Also, you can interactively test-drive these examples, e.g. against a local Kafka cluster. If you want to actually run these examples, then you must first install and run Apache Kafka and friends, which we describe in section Packaging and running the examples. Each example also states its exact requirements and instructions at the very top.
• Examples under src/test/: These examples are a bit longer because they implement integration tests that demonstrate end-to-end data pipelines. Here, we use a testing framework to automatically spawn embedded Kafka clusters, feed input data to them (using the standard Kafka producer client), process the data using Kafka Streams, and finally read and verify the output results (using the standard Kafka consumer client). These examples are also a good starting point to learn how to implement your own end-to-end integration tests.

Java

Note: We use the label "Lambda" to denote examples that make use of lambda expressions and thus require Java 8+.

• WordCountLambdaExample -- demonstrates, using the Kafka Streams DSL, how to implement the WordCount program that computes a simple word occurrence histogram from an input text.
• MapFunctionLambdaExample -- demonstrates how to perform stateless transformations via map functions, using the Kafka Streams DSL (see also the Scala variant MapFunctionScalaExample)
• SumLambdaExample -- demonstrates how to perform stateful transformations via reduceByKey, using the Kafka Streams DSL
• PageViewRegionLambdaExample -- demonstrates how to perform a join between a KStream and a KTable, i.e. an example of a stateful computation
  • Variant: PageViewRegionExample, which implements the same example but without lambda expressions and thus works with Java 7+.
• Working with data in Apache Avro format (see also the end-to-end demos under integration tests below):
  • Generic Avro: PageViewRegionLambdaExample (Java 8+) and PageViewRegionExample (Java 7+)
  • Specific Avro: WikipediaFeedAvroLambdaExample (Java 8+) and WikipediaFeedAvroExample (Java 7+)
• SecureKafkaStreamsExample -- demonstrates how to configure Kafka Streams for secure stream processing (here: encrypting data-in-transit and enabling client authentication so that the Kafka Streams application authenticates itself to the Kafka brokers)
• And further examples.

We also provide several integration tests, which demonstrate end-to-end data pipelines. Here, we spawn embedded Kafka clusters and the Confluent Schema Registry, feed input data to them (using the standard Kafka producer client), process the data using Kafka Streams, and finally read and verify the output results (using the standard Kafka consumer client).

Tip: Run mvn test to launch the integration tests.

• WordCountLambdaIntegrationTest
• JoinLambdaIntegrationTest
• MapFunctionLambdaIntegrationTest
• PassThroughIntegrationTest
• SumLambdaIntegrationTest
• GenericAvroIntegrationTest.java
• SpecificAvroIntegrationTest.java

Scala

• MapFunctionScalaExample -- demonstrates how to perform simple, state-less transformations via map functions, using the Kafka Streams DSL (see also the Java variant MapFunctionLambdaExample)

We also provide several integration tests, which demonstrate end-to-end data pipelines. Here, we spawn embedded Kafka clusters and the Confluent Schema Registry, feed input data to them (using the standard Kafka producer client), process the data using Kafka Streams, and finally read and verify the output results (using the standard Kafka consumer client).

Tip: Run mvn test to launch the integration tests.

• JoinScalaIntegrationTest
• WordCountScalaIntegrationTest

Requirements

Apache Kafka

The code in this repository requires Apache Kafka 0.10.0+ because from this point onwards Kafka includes its Kafka Streams library. See Version Compatibility Matrix for further details, as different branches of this repository may have different Kafka requirements.

When using the master branch: The master branch typically requires the latest trunk version of Apache Kafka (cf. kafka.version in pom.xml for details). The following instructions will build and locally install the latest trunk Kafka version:

$ git clone [email protected]:apache/kafka.git
$ cd kafka
$ git checkout trunk

# Bootstrap gradle wrapper
$ gradle

# Now build and install Kafka locally
$ ./gradlew clean installAll

Confluent Platform

The code in this repository requires Confluent Platform 3.0.x. See Version Compatibility Matrix for further details, as different branches of this repository may have different Confluent Platform requirements.

• Confluent Platform 3.0.0 Quickstart (how to download and install)
• Confluent Platform 3.0.0 documentation

If you just run the integration tests (mvn test), then you do not need to install anything -- all maven artifacts will be downloaded automatically for the build. However, if you want to interactively test-drive the examples under src/main/ (such as WordCountLambdaExample), then you do need to install Confluent Platform. See Packaging and running the examples below. Also, each example states its exact requirements at the very top.

Java 8

Some code examples require Java 8, primarily because of the usage of lambda expressions.

IntelliJ IDEA users:

• Open File > Project structure
• Select "Project" on the left.
  • Set "Project SDK" to Java 1.8.
  • Set "Project language level" to "8 - Lambdas, type annotations, etc."

Scala

Scala is required only for the Scala examples in this repository. If you are a Java developer you can safely ignore this section.

If you want to experiment with the Scala examples in this repository, you need a version of Scala that supports Java 8 and SAM / Java lambda (e.g. Scala 2.11 with * -Xexperimental compiler flag, or 2.12).

Packaging and running the examples

Tip: If you only want to run the integration tests (mvn test), then you do not need to package or install anything -- just run mvn test. The instructions below are only needed if you want to interactively test-drive the examples under src/main/.

The first step is to install and run a Kafka cluster, which must consist of at least one Kafka broker as well as at least one ZooKeeper instance. Some examples may also require a running instance of Confluent schema registry. The Confluent Platform 3.0.0 Quickstart guide provides the full details.

In a nutshell:

# Start ZooKeeper
$ ./bin/zookeeper-server-start ./etc/kafka/zookeeper.properties

# In a separate terminal, start Kafka broker
$ ./bin/kafka-server-start ./etc/kafka/server.properties

# In a separate terminal, start Confluent schema registry
$ ./bin/schema-registry-start ./etc/schema-registry/schema-registry.properties

# Again, please refer to the Confluent Platform Quickstart for details such as
# how to download Confluent Platform, how to stop the above three services, etc.

Tip: You can also run mvn test, which executes the included integration tests. These tests spawn embedded Kafka clusters to showcase the Kafka Streams functionality end-to-end. The benefit of the integration tests is that you don't need to install and run a Kafka cluster yourself.

If you want to run the examples against a Kafka cluster, you may want to create a standalone jar ("fat jar") of the Kafka Streams examples via:

# Create a standalone jar
#
# Tip: You can also disable the test suite (e.g. to speed up the packaging
#      or to lower JVM memory usage) if needed:
#
#     $ mvn -DskipTests=true clean package
#
$ mvn clean package

# >>> Creates target/streams-examples-3.0.0-standalone.jar

You can now run the example applications as follows:

# Run an example application from the standalone jar.
# Here: `WordCountLambdaExample`
$ java -cp target/streams-examples-3.0.0-standalone.jar \
  io.confluent.examples.streams.WordCountLambdaExample

Keep in mind that the machine on which you run the command above must have access to the Kafka/ZK clusters you configured in the code examples. By default, the code examples assume the Kafka cluster is accessible via localhost:9092 (Kafka broker) and the ZooKeeper ensemble via localhost:2181.

Development

This project uses the standard maven lifecycle and commands such as:

$ mvn compile # This also generates Java classes from the Avro schemas
$ mvn test    # But no tests yet!

Version Compatibility Matrix

The master branch of this repository represents active development, and may require additional steps on your side to make it compile. Check this README as well as pom.xml for any such information.