[jira] [Created] (KAFKA-13837) Return error for Fetch requests from unrecognized followers

["Jason Gustafson (Jira)" <ji...@apache.org>]

Jason Gustafson created KAFKA-13837:
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             Summary: Return error for Fetch requests from unrecognized followers
                 Key: KAFKA-13837
                 URL: https://issues.apache.org/jira/browse/KAFKA-13837
             Project: Kafka
          Issue Type: Bug
            Reporter: Jason Gustafson
            Assignee: Jason Gustafson


If the leader of a partition receives a request from a replica which is not in the current replica set, we currently return an empty fetch response with no error. I think the rationale for this is that the leader may not have received the latest `LeaderAndIsr` update which adds the replica, so we just want the follower to retry. The problem with this is that if the `LeaderAndIsr` request never arrives, then there might not be an external indication of a problem. This probably was the only reasonable option before we added the leader epoch to the `Fetch` request API. Now that we have it, it would be clearer to return an `UNKNOWN_LEADER_EPOCH` error to indicate that the (replicaId, leaderEpoch) tuple is not recognized. 



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