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./bin/kafka-invoke-consumer-rebalance.sh --zookeeper localhost:2181 2181 --broker 1 --group-id  group-1 will immediately trigger a consumer group rebalance by transiting group state to PREPARE_REBALANCE. (explanation in next section.)

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InvokeConsumerRebalance (introduced above) will trigger one rebalance immediately on static membership, which is mainly used for fast scale down/host replacement cases (we detect consumer failure faster than the session timeout). This API will first send a FindCoordinatorRequest to locate the target broker, and initiate a ConsumerRebalanceRequest to group target broker hosting that coordinator, and the coordinator will decide whether to take this metadata change request based on its status at time.

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We need to enforce special access to these APIs to the end user who may not be in administrative role of Kafka Cluster. We shall allow a similar access level to the join group request, so the consumer service owner could easily use this API. Another detail to take care is that we need to automatically take the hash of group id so that we know which broker to send this request to.

Compatibility, Deprecation, and Migration Plan

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