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.

./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 quarantinedTest  # runs the quarantined tests

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

./gradlew clients:test --tests RequestResponseTest

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

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

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.

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.

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

./gradlew clean releaseTarGz

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

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

./gradlew clean

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 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.

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>
 ...

./gradlew -PskipSigning=true :streams:publishToMavenLocal

./gradlew testJar

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 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).

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 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 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.

./gradlew dependencyUpdates

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: maximum number of test processes to start in parallel. Defaults to the number of processors available to the JVM.
• maxScalacThreads: maximum number of worker threads for the scalac backend. Defaults to the lowest of 8 and the number of processors available to the JVM. The value must be between 1 and 16 (inclusive).
• 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: 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).
• keepAliveMode: configures the keep alive mode for the Gradle compilation daemon - reuse improves start-up time. The values should be one of daemon or session (the default is daemon). daemon keeps the daemon alive until it's explicitly stopped while session keeps it alive until the end of the build session. This currently only affects the Scala compiler, see https://github.com/gradle/gradle/pull/21034 for a PR that attempts to do the same for the Java compiler.
• scalaOptimizerMode: configures the optimizing behavior of the scala compiler, the value should be one of none, method, inline-kafka or inline-scala (the default is inline-kafka). none is the scala compiler default, which only eliminates unreachable code. method also includes method-local optimizations. inline-kafka adds inlining of methods within the kafka packages. Finally, inline-scala also includes inlining of methods within the scala library (which avoids lambda allocations for methods like Option.exists). inline-scala is only safe if the Scala library version is the same at compile time and runtime. Since we cannot guarantee this for all cases (for example, users may depend on the kafka jar for integration tests where they may include a scala library with a different version), we don't enable it by default. See https://www.lightbend.com/blog/scala-inliner-optimizer for more details.

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