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As part of the KIP-500 initiative, we need to build a bridge release version of Kafka that could isolate the direct Zookeeper write access only to the controller. Protocols that alter cluster/topic configurations, security configurations or quotas, topics etc, should be migrated for sure as they are still relying on arbitrary broker to Zookeeper write access.

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• AlterConfig

• IncrementalAlterConfig 

• CreateAcls

• DeleteAcls

• AlterClientQuotas

• CreateDelegationToken

• RenewDelegationToken 

• ExpireDelegationToken

Partially Change FindCoordinator Request Routing 

One edge case we also would like to fix is for the FindCoordinator protocol. It has a special internal topic creation logic when the cluster receives the request for the first time as transaction log topic and consumer offset topic are lazily initialized. Currently the target broker shall just utilize its own ZK client to create topic, which is disallowed in the bridge release. For this scenario, non-controller broker shall just forward a CreateTopicRequest to the controller instead and let controller take care of the rest, while waiting for the response in the mean time. 

Public Interfaces

We are going to bump all mentioned APIs above by one version, and new admin client was expected to only talk to the controller. For example we bump the AlterConfig API to v2.

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