Status

Current state: Under Discussion Accepted

Discussion thread: https://lists.apache.org/thread/m6m1qng5v9q8dd1mng0sygc9x83mx8kn

Voting thread: https://lists.apache.org/thread/w1myl1hsmd5bdko6y8y2fdtzvtcsfh13Discussion thread: N/A

JIRA:

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The group.coordinator.rebalance.protocols configuration will be deprecated in Kafka 4.3 and removed in version 5.0, following the same approach as Share Groups. The configuration will be decoupled from feature functionality, meaning it will be accepted but ignored during the transition period. Both New Group Coordinator and Streams will follow the Share Groups model, where functionality is controlled solely by group.version  and streams.version  feature features via kafka-features.sh. During the deprecation period, if users are missing any of default values "classic, consumer, streams", a warning will inform them that this config will be deprecated and they cannot disable a protocol with it in version 5.0.

This eliminates the dual requirement of setting both configuration and feature flags, providing a consistent experience across all coordinator types. Users should use kafka-features.sh for all feature version management , and can safely remove the this configuration from their server.properties files, as it no longer affects feature functionality.

Compatibility, Deprecation, and Migration Plan

For the group coordinator, after users upgrade, the system will maintain the same version as before the upgrade because feature information is persisted. Users can upgrade using kafka-features.sh without concern for the config value, as it has been decoupled from the feature version.

Current Status (Kafka 4.2 - Upcoming Release)

Share Groups has already deprecated and decoupled from this configuration (though still listed in valid values in the config description). 
Both Group Coordinator and Streams rebalance protocol are currently controlled by both the group.coordinator.rebalance.protocols  configuration and their respective feature flags (`group.version` and `streams.version`).

Deprecation Timeline

Kafka 4.3 (Deprecation Period):

As described in the Proposed Changes, if users explicitly set group.coordinator.rebalance.protocols  with values missing any of the defaults (classic, consumer, streams), users can still disable protocols, but will receive a deprecation warning advising them to either:
- Use the default values (classic, consumer, streams), or
- Remove the configuration

Kafka 5.0 (Removal):
This configuration will be completely removed. Any protocols previously disabled via this configuration will become available, as protocol control will be managed exclusively through feature flagsAs for Share Groups and Streams rebalance protocol, the same applies. Additionally, since neither has reached general access yet, there are no migration concerns.

Test Plan

This change will be validated through unit and integration tests

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