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Compatibility, deprecation, and migration plan

The features in this KIP RPC versions will be supported if negotiated using the ApiVersions of all of the voters and observers is greater than the versions described here. If the leader has a replica UUID for all of the voters then this KIP is supported by all of the voters RPC. KRaft will use the kraft.version to determine which version of KRaftVersionRecord and VotersRecord to write to the log and which version of QuorumStateData to write to the quorum-state file.

Downgrading the kraft.version from 1 to 0 is not possible. This is mainly due to the fact that kraft.version 1 writes data to the log and snapshot that gets replicated to all of the replicas.

When to remove controller.quorum.voters

It is safe for the operator to remove the configuration for controller.qourumquorum.voters when the kraft.version has been upgrade to version 1. All of the Kafka nodes will expose the ignored-static-voter metrics. If all of the Kafka nodes expose a 1 for this metrics, it is safe to remove controller.quorum.voters from the node configuration and specify the controller.quorum.bootstrap.servers instead.

Test plan

This KIP will be tested using unittest, integration tests, system test, simulation tests and TLA+ specification.

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