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The KIP adds a per-member field called Reason to the LeaveGroupRequest. The field will be populated with the leaving reason by the Consumer when it wants to leave the group. The consumer already logs the reason so we will reuse the same message. The field will be populated by the AdminClient as well when removeMembersFromConsumerGroup is called. In this case, the reason will be "member was removed by an admin" by default or the provided reason prefixed by "member was removed by an admin".

The KIP also adds a field called Reason to the JoinGroupRequest. The field will be populated with the reason why the joining reason by the Consumer. This will be really helpful to understand why a rebalance is triggered. The field will be populated by the Consumer as well when enforceRebalance is called. In this case, the reason will be "rebalance enforced by user" by default or the provided reason prefixed by "rebalance enforced by user:".

Compatibility, Deprecation, and Migration Plan

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