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See our web site for details on the project.

You need to have Java installed.

We build and test Apache Kafka with 17 and 23. The release parameter in javac and scalac is set to 11 for the clients and streams modules, and 17 for the broker and tools, ensuring compatibility with their respective minimum Java versions.

Scala 2.13 is the only supported version in Apache Kafka.

Build a jar and run it

./gradlew jar

Follow instructions in https://kafka.apache.org/quickstart

Build source jar

./gradlew srcJar

Build aggregated javadoc

./gradlew aggregatedJavadoc

Build javadoc and scaladoc

./gradlew javadoc
./gradlew javadocJar # builds a javadoc jar for each module
./gradlew scaladoc
./gradlew scaladocJar # builds a scaladoc jar for each module
./gradlew docsJar # builds both (if applicable) javadoc and scaladoc jars for each module

Run unit/integration tests

./gradlew test  # runs both unit and integration tests
./gradlew unitTest
./gradlew integrationTest
./gradlew quarantinedTest  # runs the quarantined tests

Force re-running tests without code change

./gradlew test --rerun-tasks
./gradlew unitTest --rerun-tasks
./gradlew integrationTest --rerun-tasks

Running a particular unit/integration test

./gradlew clients:test --tests RequestResponseTest

Repeatedly running a particular unit/integration test with specific times by setting N

N=500; I=0; while [ $I -lt $N ] && ./gradlew clients:test --tests RequestResponseTest --rerun --fail-fast; do (( I=$I+1 )); echo "Completed run: $I"; sleep 1; done

Running a particular test method within a unit/integration test

./gradlew core:test --tests kafka.api.ProducerFailureHandlingTest.testCannotSendToInternalTopic
./gradlew clients:test --tests org.apache.kafka.clients.MetadataTest.testTimeToNextUpdate

Running a particular unit/integration test with log4j output

By default, there will be only small number of logs output while testing. You can adjust it by changing the log4j2.yml file in the module's src/test/resources directory.

For example, if you want to see more logs for clients project tests, you can modify the line in clients/src/test/resources/log4j2.yml to level: INFO and then run:

./gradlew cleanTest clients:test --tests NetworkClientTest

And you should see INFO level logs in the file under the clients/build/test-results/test directory.

Specifying test retries

Retries are disabled by default, but you can set maxTestRetryFailures and maxTestRetries to enable retries.

The following example declares -PmaxTestRetries=1 and -PmaxTestRetryFailures=3 to enable a failed test to be retried once, with a total retry limit of 3.

./gradlew test -PmaxTestRetries=1 -PmaxTestRetryFailures=3

The quarantinedTest task also has no retries by default, but you can set maxQuarantineTestRetries and maxQuarantineTestRetryFailures to enable retries, similar to the test task.

./gradlew quarantinedTest -PmaxQuarantineTestRetries=3 -PmaxQuarantineTestRetryFailures=20

See Test Retry Gradle Plugin for and build.yml more details.

Generating test coverage reports

Generate coverage reports for the whole project:

./gradlew reportCoverage -PenableTestCoverage=true -Dorg.gradle.parallel=false

Generate coverage for a single module, i.e.:

./gradlew clients:reportCoverage -PenableTestCoverage=true -Dorg.gradle.parallel=false

Building a binary release gzipped tar ball

./gradlew clean releaseTarGz

The release file can be found inside ./core/build/distributions/.

Building auto generated messages

Sometimes it is only necessary to rebuild the RPC auto-generated message data when switching between branches, as they could fail due to code changes. You can just run:

./gradlew processMessages processTestMessages

Running a Kafka broker in KRaft mode

Using compiled files:

KAFKA_CLUSTER_ID="$(./bin/kafka-storage.sh random-uuid)"
./bin/kafka-storage.sh format --standalone -t $KAFKA_CLUSTER_ID -c config/kraft/reconfig-server.properties
./bin/kafka-server-start.sh config/kraft/reconfig-server.properties

Using docker image:

docker run -p 9092:9092 apache/kafka:3.7.0

Cleaning the build

./gradlew clean

Running a task for a specific project

This is for core, examples and clients

./gradlew core:jar
./gradlew core:test

Streams has multiple sub-projects, but you can run all the tests:

./gradlew :streams:testAll

Listing all gradle tasks

./gradlew tasks

Building IDE project

Note Please ensure that JDK17 is used when developing Kafka.

Note that this is not strictly necessary (IntelliJ IDEA has good built-in support for Gradle projects, for example).

./gradlew eclipse
./gradlew idea

The eclipse task has been configured to use ${project_dir}/build_eclipse as Eclipse's build directory. Eclipse's default build directory (${project_dir}/bin) clashes with Kafka's scripts directory and we don't use Gradle's build directory to avoid known issues with this configuration.

IntelliJ Language Level awareness:

IntelliJ will automatically check Java syntax and compatibility for each module, even if the Java version is not explicitly set in the Structure > Project Settings > Modules.

Publishing the streams quickstart archetype artifact to maven

For the Streams archetype project, one cannot use gradle to upload to maven; instead the mvn deploy command needs to be called at the quickstart folder:

cd streams/quickstart
mvn deploy

Please note for this to work you should create/update user maven settings (typically, ${USER_HOME}/.m2/settings.xml) to assign the following variables

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
                       https://maven.apache.org/xsd/settings-1.0.0.xsd">
...                           
<servers>
   ...
   <server>
      <id>apache.snapshots.https</id>
      <username>${maven_username}</username>
      <password>${maven_password}</password>
   </server>
   <server>
      <id>apache.releases.https</id>
      <username>${maven_username}</username>
      <password>${maven_password}</password>
    </server>
    ...
 </servers>
 ...

Installing specific projects to the local Maven repository

./gradlew -PskipSigning=true :streams:publishToMavenLocal

Building the test jar

./gradlew testJar

Running code quality checks

There are two code quality analysis tools that we regularly run, spotbugs and checkstyle.

Checkstyle

Checkstyle enforces a consistent coding style in Kafka. You can run checkstyle using:

./gradlew checkstyleMain checkstyleTest spotlessCheck

The checkstyle warnings will be found in reports/checkstyle/reports/main.html and reports/checkstyle/reports/test.html files in the subproject build directories. They are also printed to the console. The build will fail if Checkstyle fails. For experiments (or regression testing purposes) add -PcheckstyleVersion=X.y.z switch (to override project-defined checkstyle version).

Spotless

The import order is a part of static check. please call spotlessApply to optimize the imports of Java codes before filing pull request.

./gradlew spotlessApply

Spotbugs

Spotbugs uses static analysis to look for bugs in the code. You can run spotbugs using:

./gradlew spotbugsMain spotbugsTest -x test

The spotbugs warnings will be found in reports/spotbugs/main.html and reports/spotbugs/test.html files in the subproject build directories. Use -PxmlSpotBugsReport=true to generate an XML report instead of an HTML one.

JMH microbenchmarks

We use JMH to write microbenchmarks that produce reliable results in the JVM.

See jmh-benchmarks/README.md for details on how to run the microbenchmarks.

Dependency Analysis

The gradle dependency debugging documentation mentions using the dependencies or dependencyInsight tasks to debug dependencies for the root project or individual subprojects.

Alternatively, use the allDeps or allDepInsight tasks for recursively iterating through all subprojects:

./gradlew allDeps

./gradlew allDepInsight --configuration runtimeClasspath --dependency com.fasterxml.jackson.core:jackson-databind

These take the same arguments as the builtin variants.

Determining if any dependencies could be updated

./gradlew dependencyUpdates

Common build options

The following options should be set with a -P switch, for example ./gradlew -PmaxParallelForks=1 test.

Running system tests

See tests/README.md.

Running in Vagrant

See vagrant/README.md.

Contribution

Apache Kafka is interested in building the community; we would welcome any thoughts or patches. You can reach us on the Apache mailing lists.

To contribute follow the instructions here: