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Following KIP-1022: Formatting and Updating Features, the group.coordinator.rebalance.protocols server configuration has become redundant. KIP-848 (New Group Coordinator), KIP-932 (Share groupsGroup), and KIP-1071 (Streams rebalance protocol) now implement group.version , streams.version , and share.version  respectively. These feature versions enable cluster-wide upgrades and downgrades through kafka-features.sh, eliminating the need for server-level configuration to control feature versions.

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• org.apache.kafka.coordinator.group.GroupCoordinatorConfig.GROUP_COORDINATOR_REBALANCE_PROTOCOLS_CONFIG

Proposed Changes

The group.coordinator.rebalance.protocols configuration will be deprecated in Kafka 4.x 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 via kafka-features.sh. 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 configuration from their server.properties files as it no longer affects feature functionality.

Compatibility, Deprecation, and Migration Plan

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As 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

Rejected Alternatives

References

• KIP-848: The Next Generation of the Consumer Rebalance Protocol
• KIP-932: Queues for Kafka (Share Group)
• KIP-1022: Formatting and Updating Features
• KIP-1071: Streams Rebalance Protocol for Kafka Streams