Chapter 5. Kafka breaking changes

From Kafka 4.0, ZooKeeper is no longer supported. Kafka clusters must operate in KRaft mode.

Kafka MirrorMaker 1 has been removed in Kafka 4.0. MirrorMaker 2 is the only version available. MirrorMaker 2 is based on the Kafka Connect framework, connectors managing the transfer of data between clusters.

If you’re using MirrorMaker 1, you can replicate its functionality in MirrorMaker 2 by using the IdentityReplicationPolicy class. By default, MirrorMaker 2 renames topics replicated to a target cluster, but IdentityReplicationPolicy preserves the original topic names, enabling the same active/passive unidirectional replication as MirrorMaker 1.

The auto.include.jmx.reporter configuration has been removed in Kafka. From Kafka 4.0, to enable the JMXReporter you must either enable metrics in .spec.kafka.metrics, or explicitly add JMXReporter in metric.reporters.

Logging framework has been migrated from Log4j to Log4j2. If you have any custom logging configuration, you might need to update it during the upgrade to Kafka 4.0.