Upgrade pages for moving between Kafka 4.x releases on KRaft, based on the Kafka upgrade notes and release plan.
Upgrading a KRaft cluster between 4.x releases, for example 4.1 to 4.3: supported upgrade paths, broker-by-broker rollout, finalizing the release version with kafka-features, client compatibility and rollback limits. Separate from the ZooKeeper to KRaft migration.
The big jump to Kafka 4: ZooKeeper removal and the KRaft prerequisite, Java 17 for brokers and Connect, removed pre-0.10 protocols, the KIP-848 consumer protocol becoming available, and the order to upgrade controllers, brokers and clients.
Finding clients that will break on Kafka 4: the compatibility matrix for 0.x to 2.0, 2.1 to 2.8 and 3.x clients, Streams and Connect limits, librdkafka and framework versions, and how to inventory client versions before the upgrade.
Switching from controller.quorum.voters to KIP-853 dynamic quorums: checking kraft.version with kafka-features, the upgrade steps, then adding and removing controllers with kafka-metadata-quorum without downtime.
The last step of every KRaft upgrade: when to run kafka-features upgrade, what finalizing enables, which features can be downgraded afterwards and how to plan a rollback window.
Upgrading the components around the brokers: Java 17 for Connect workers, connector plugin compatibility and plugin discovery modes, Streams rebalance protocol changes, and rolling Connect clusters without losing tasks.
Planning upgrades when Strimzi runs Kafka: matching operator releases to supported Kafka versions, upgrading the operator before Kafka, changing the Kafka version in the custom resource and checking Kubernetes version support.
Getting an old ZooKeeper-based cluster to Kafka 4: the hop to 3.9 as the bridge release, the KRaft migration, the 3.3.x minimum for KRaft clusters, client upgrades along the way and how long each step takes.
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