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As discussed in KIP-500 and the follow-on KIPs, KRaft clusters expose the same public APIs as ZK-based Kafka clusters. Since the modern Kafka producer and consumer do not directly access ZooKeeper, no changes are needed to existing Kafka clients. While some administrative tools still have options which enable them to perform access to ZooKeeper, this mode of access has been deprecated since mid-2020, as described in KIP-555. Therefore, we think the transition for clients should be smooth.

Bridge Releases

Starting with 3.4, all the 3.x releases will be "bridge releases" as described in KIP-500. What this means is that they can act as a bridge from the ZK world to the KRaft world.

Users who have a ZooKeeper-based Kafka and want to upgrade to a post-ZK version (4.0 and beyond) will have to first upgrade to one of these bridge releases. Then, once they are in KRaft mode, they will be able to upgrade to any 4.x release.

Potential Objections and Responses

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