# GraalVM Based Native Apache Kafka Docker Image

## Introduction
- The Native Apache Kafka Docker Image can launch brokers with sub-second startup time and minimal memory footprint by leveraging native Kafka executable.
- The native Kafka executable is built by compiling Apache Kafka code ahead-of-time using the [GraalVM native-image tool](https://www.graalvm.org/jdk21/reference-manual/native-image/).
- This image is experimental and intended for local development and testing purposes only; it is not recommended for production use.
- This is introduced with [KIP-974](https://cwiki.apache.org/confluence/display/KAFKA/KIP-974%3A+Docker+Image+for+GraalVM+based+Native+Kafka+Broker).

## Native-Image reachability metadata
The native-image tool performs static analysis while building a native binary to determine the dynamic features(the dynamic language features of the JVM, including reflection and resource handling, compute the dynamically-accessed program elements such as invoked methods or resource URLs at runtime), but it cannot always exhaustively predict all uses. 
To ensure inclusion of these elements into the native binary, reachability metadata should be provided to the native-image builder. 
These metadata configs are provided in the `native-image-configs` directory.

## How to generate reachability metadata
GraalVM provide an option to create these configs automatically by running the application normally with the [native-image agent](https://www.graalvm.org/latest/reference-manual/native-image/metadata/AutomaticMetadataCollection/) attached.
The configs in the `native-image-configs` directory are generated by running existing Apache Kafka System Tests(using GraalVM JIT and attaching the native-image agent to the process) as they are quite exhaustive.

To update reachability metadata, users can set following environment variable and run related jar files. New metadata configs will be generated in the `native-image-configs` directory.
```bash
export JAVA_TOOL_OPTIONS="-agentlib:native-image-agent=config-merge-dir=/path/to/kafka/docker/native/native-image-configs"
```

## Limitations of Native Apache Kafka executable
- Dynamic Features: For any new dynamic feature added or modified in Apache Kafka, the corresponding metadata configurations must be added or updated in the `native-image-configs`. As of now these configs are static.
- Runtime Jars: Native Kafka Executable does not support capabilities that require a new runtime jar provided by the user, as the jar's information is not available during build time. In such cases, a new native Kafka binary must be built, including that jar in the classpath during the build.
- Garbage Collection: This implementation uses the community edition of GraalVM, which supports only `serial` GC. Therefore, Native Apache Kafka supports `serial` GC and not `G1` GC.

## How to use this image in docker container
Check out [this](../examples/README.md) guide.

## How to build, test and release this docker image
Check out [this](../README.md) guide.

## How to run system tests on native Apache Kafka
Check out [this](../../tests/README.md#running-tests-using-docker) guide.

