[KAFKA-13837] Return error for Fetch requests from unrecognized followers

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.3.0
• Assignee: Jason Gustafson
• Reporter: Jason Gustafson
• Created: 19/Apr/22 21:05
• Updated: 19/May/22 03:58
• Resolved: 19/May/22 03:58

Description

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. 

Issue Links

• links to: GitHub Pull Request #12150