See our web site for details on the project.

You need to have Java installed.

We build and test Apache Kafka with Java 8, 11 and 15. We set the release parameter in javac and scalac to 8 to ensure the generated binaries are compatible with Java 8 or higher (independently of the Java version used for compilation).

Scala 2.13 is used by default, see below for how to use a different Scala version or all of the supported Scala versions.

./gradlew jar

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

./gradlew srcJar

./gradlew aggregatedJavadoc

./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

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

./gradlew cleanTest test
./gradlew cleanTest unitTest
./gradlew cleanTest integrationTest

./gradlew clients:test --tests RequestResponseTest

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

Change the log4j setting in either clients/src/test/resources/log4j.properties or core/src/test/resources/log4j.properties

./gradlew clients:test --tests RequestResponseTest

By default, each failed test is retried once up to a maximum of five retries per test run. Tests are retried at the end of the test task. Adjust these parameters in the following way:

./gradlew test -PmaxTestRetries=1 -PmaxTestRetryFailures=5

See Test Retry Gradle Plugin for more details.

Generate coverage reports for the whole project:

./gradlew reportCoverage -PenableTestCoverage=true

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

./gradlew clients:reportCoverage -PenableTestCoverage=true

./gradlew clean releaseTarGz

The above command will fail if you haven't set up the signing key. To bypass signing the artifact, you can run:

./gradlew clean releaseTarGz -x signArchives

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

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

./gradlew clean

Note that if building the jars with a version other than 2.13.x, you need to set the SCALA_VERSION variable or change it in bin/kafka-run-class.sh to run the quick start.

You can pass either the major version (eg 2.12) or the full version (eg 2.12.7):

./gradlew -PscalaVersion=2.12 jar
./gradlew -PscalaVersion=2.12 test
./gradlew -PscalaVersion=2.12 releaseTarGz

Invoke the gradlewAll script followed by the task(s):

./gradlewAll test
./gradlewAll jar
./gradlewAll releaseTarGz

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

./gradlew tasks

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.

./gradlewAll uploadArchives

Please note for this to work you should create/update ${GRADLE_USER_HOME}/gradle.properties (typically, ~/.gradle/gradle.properties) and assign the following variables

mavenUrl=
mavenUsername=
mavenPassword=
signing.keyId=
signing.password=
signing.secretKeyRingFile=

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>
 ...

./gradlewAll install

./gradlew testJar

./gradlew core:dependencies --configuration runtime

./gradlew dependencyUpdates

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

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

./gradlew checkstyleMain checkstyleTest

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.

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.

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.

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

• commitId: sets the build commit ID as .git/HEAD might not be correct if there are local commits added for build purposes.
• mavenUrl: sets the URL of the maven deployment repository (file://path/to/repo can be used to point to a local repository).
• maxParallelForks: limits the maximum number of processes for each task.
• ignoreFailures: ignore test failures from junit
• showStandardStreams: shows standard out and standard error of the test JVM(s) on the console.
• skipSigning: skips signing of artifacts.
• testLoggingEvents: unit test events to be logged, separated by comma. For example ./gradlew -PtestLoggingEvents=started,passed,skipped,failed test.
• xmlSpotBugsReport: enable XML reports for spotBugs. This also disables HTML reports as only one can be enabled at a time.
• maxTestRetries: the maximum number of retries for a failing test case.
• maxTestRetryFailures: maximum number of test failures before retrying is disabled for subsequent tests.
• enableTestCoverage: enables test coverage plugins and tasks, including bytecode enhancement of classes required to track said coverage. Note that this introduces some overhead when running tests and hence why it's disabled by default (the overhead varies, but 15-20% is a reasonable estimate).

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 runtime --dependency com.fasterxml.jackson.core:jackson-databind

These take the same arguments as the builtin variants.

See tests/README.md.

See vagrant/README.md.

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:

• https://kafka.apache.org/contributing.html