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Discussion thread:  here

Vote thread:  here

JIRA:   https://issues.apache.org/jira/browse/KAFKA-20402

PR:    https://github.com/apache/kafka/pull/21961

Motivation

Consumer group rebalance is one of the most critical lifecycle events for Kafka consumers, because it directly affects users' message consume behavior. At the same time, Kafka is recommending and adopting server-side rebalance.

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Server load the group.consumer.rebalance.listener.classes when startuping and trigger the callback interface when rebalance happened.

Refer to the PR example:

Note:  Cover all non-classic consume group due to the classic consume group will be deprecated soon.

Compatibility, Deprecation, and Migration Plan 

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