Agent Guide for Apache Kafka

This file is read by automated agents (security scanners, code analyzers, AI assistants) operating on this repository.

Project overview

Apache Kafka is a distributed event streaming platform. This repo is a Gradle build in Java and Scala 2.13.

Supported JDK: 11+ for clients, generator, and streams; 17+ for other modules.
Build/test JDK: Java 17 and 25.
Build tool: Gradle, wrapper ./gradlew is recommended.

Repository layout (high level)

Path	Purpose
`clients/`	Producer, consumer, admin client APIs and protocol messages
`core/`	Broker runtime, log, replication, request handling (gradually being removed along with Scala code)
`server/`, `server-common/`	Broker/server components and shared server code
`metadata/`, `raft/`	KRaft metadata layer and Raft implementation
`storage/`, `storage/api/`	Log segments, checkpoints, tiered storage APIs
`group-coordinator/`, `share-coordinator/`, `transaction-coordinator/`, `coordinator-common/`	Coordinators
`connect/`	Kafka Connect (api, runtime, plugins, transforms)
`streams/`	Kafka Streams (+ Scala, examples, upgrade system tests)
`generator/`	RPC/message code generation
`tools/`, `shell/`	CLI tools and kafka metadata shell
`examples/`	Kafka producer and consumer examples
`jmh-benchmarks/`	Kafka benchmarks tests
`trogdor/`	test framework
`tests/`	System test harness (see `tests/README.md`)
`config/`	Sample broker/controller configuration
`checkstyle/`	Checkstyle rules and import-control XML
`docs/`	Documentation sources
`docker/`	Docker images, build/test scripts, and examples for JVM and native Kafka

Build commands

# Compile jars
./gradlew jar

# Release tarball (output under core/build/distributions/)
./gradlew clean releaseTarGz

# Publish to local Maven (skip signing for local dev)
./gradlew -PskipSigning=true publishToMavenLocal

# Regenerate RPC/message classes after branch switches
./gradlew processMessages processTestMessages

# List tasks
./gradlew tasks

Module-scoped build:

./gradlew core:jar
./gradlew clients:jar
./gradlew :streams:testAll

Test commands

# All unit + integration tests
./gradlew test

# Split suites
./gradlew unitTest
./gradlew integrationTest

# Include flaky tests (marked @Flaky)
./gradlew test -Pkafka.test.run.flaky=true

# Re-run without considering up-to-date
./gradlew test --rerun-tasks

# Single test class
./gradlew clients:test --tests RequestResponseTest

# Single test method
./gradlew core:test --tests kafka.api.ProducerFailureHandlingTest.testCannotSendToInternalTopic

# Coverage (whole project or one module)
./gradlew reportCoverage -PenableTestCoverage=true -Dorg.gradle.parallel=false
./gradlew clients:reportCoverage -PenableTestCoverage=true -Dorg.gradle.parallel=false

Test retries (optional): -PmaxTestRetries=1 -PmaxTestRetryFailures=3

Logging: adjust log4j2.yaml under <module>/src/test/resources/ for verbose test logs.

System tests: see tests/README.md.

Code quality

Run before submitting Java changes:

./gradlew spotlessApply          # fix import order / formatting
./gradlew checkstyleMain checkstyleTest spotlessCheck
./gradlew spotbugsMain spotbugsTest -x test   # optional static analysis

Checkstyle reports: <module>/build/reports/checkstyle/.

Coding conventions

Commits / PR titles: Start with KAFKA-XXXXX, MINOR, or HOTFIX. Use KAFKA-XXXXX only when there is a valid Jira ticket for the change.
AI-generated contributions: Follow the AI-Generated Contributions section in CONTRIBUTING.md — add a Co-Authored-By or Generated-by commit trailer for AI-assisted changes.
Public API / KIP: Changes to public interfaces, wire protocol, configurations, or metrics generally require a KIP. See the javadoc include list in build.gradle for packages treated as public API.
License header: New source files need the standard ASF license header (see existing files in the same module).
Checkstyle: Enforced on main and test sources; rules in checkstyle/. Import order is checked via Spotless.
Generated code: Do not hand-edit generated RPC/message sources. Regenerate with processMessages / processTestMessages. See clients/src/main/resources/common/message/README.md.
Scope: Prefer targeted unit tests in the module you change; integration/system tests for cross-component behavior.
Compatibility: clients, generator, and streams modules support Java 11+; all other modules require Java 17+. Avoid APIs that break those release levels.

Security

See SECURITY.md for how to report a vulnerability and for links to the Apache Kafka security model under docs/security/.

Agents that scan this repository should consult SECURITY.md and the linked security model before reporting issues. In particular, the core model defines what is in and out of scope, how reports are classified, and a list of known non-findings; each component page adds its own known non-findings.

Reference docs

Topic	Location
Build, test, broker quickstart	README.md
Contributing	CONTRIBUTING.md, https://kafka.apache.org/contributing.html
Message protocol / codegen	clients/src/main/resources/common/message/README.md
System tests	tests/README.md
JMH benchmarks	jmh-benchmarks/README.md
Client examples	examples/README.md
Security	SECURITY.md