[VOTE] 4.0.0 RC0

[David Jacot]

Hello Kafka users, developers and client-developers,

This is the first candidate for release of Apache Kafka 4.0.0. We
still have some remaining blockers but we figured that getting a first
release candidate will help the community to test this major release.

- This is the first release without Apache Zookeeper
- The Next Generation of the Consumer Rebalance Protocol is Generally Available
- The Transactions Server-Side Defense (Phase 2) is Generally Available
- Queues for Kafka is in Early Access
- Kafka uses log4j2
- Drop broker and tools support for Java 11
- Remove old client protocol API versions

Release notes for the 4.0.0 release:
https://dist.apache.org/repos/dist/dev/kafka/4.0.0-rc0/RELEASE_NOTES.html

*** Please download and test the release. Voting is not necessary as
we still have blockers.

Kafka's KEYS file containing PGP keys we use to sign the release:
https://kafka.apache.org/KEYS

* Release artifacts to be voted upon (source and binary):
https://dist.apache.org/repos/dist/dev/kafka/4.0.0-rc0/

* Docker release artifacts to be voted upon:
apache/kafka:4.0.0-rc0
apache/kafka-native:4.0.0-rc0 (Building the native image failed, I
need to investigate it)

* Maven artifacts to be voted upon:
https://repository.apache.org/content/groups/staging/org/apache/kafka/

* Javadoc:
https://dist.apache.org/repos/dist/dev/kafka/4.0.0-rc0/javadoc/

* Tag to be voted upon (off 4.0 branch) is the 4.0.0 tag:
https://github.com/apache/kafka/releases/tag/4.0.0-rc0

* Documentation:
https://kafka.apache.org/40/documentation.html

* Protocol:
https://kafka.apache.org/40/protocol.html

* Successful CI builds for the 4.0 branch:
Unit/integration tests: https://github.com/apache/kafka/actions/runs/13459676207
System tests: TBD

* Successful Docker Image Github Actions Pipeline for 4.0 branch:
Docker Build Test Pipeline (JVM):
https://github.com/apache/kafka/actions/runs/13471603921
Docker Build Test Pipeline (Native):
https://github.com/apache/kafka/actions/runs/13471605941

/**************************************

Thanks,
David

[Ismael Juma]

Thanks David! A few ideas of things to test:

1. Test clients and streams with Java 11: this is the first time we use a different Java version for clients/streams vs the rest, so it would be good to ensure the generated artifacts are good when it comes to this.

2. Similarly, test brokers and connect (including some community connectors) with Java 17.

3. Test community clients (librdkafka & related, kafka-python, sarama, segment io, etc.) with Apache 4.0.

4. Check that logging is as you expect both with your existing log4j config and the new config that is now included with the distribution - the new config uses a native log4j2 config while the existing one would rely on the compatibility layer.

5. Run the quickstarts and look for zk specific things in the quickstarts or other documentation.

6. Follow the upgrade documentation and verify that upgrades work from older versions (3.3 or higher).

7. Check that the examples still work (i.e. they were not relying on deprecated apis that have since been removed).

8. Verify that performance of your applications remains the same or has improved (both client and server-side).

Ismael