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One edge case we would also 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. 

Routing Request Security

For older requests that need redirection, forwarding broker will just use its own authorizer to verify the principals. When the request looks good, it will just forward the request with its own credentials, no second validation needed. The only exceptional case is the controller audit log which needs a principal name of the request, so we will add an optional tag called "PrincipalName" to the header when sending the proxy request.

Public Interfaces

Protocol

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Bumps

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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