[jira] [Created] (KAFKA-15372) MM2 rolling restart can drop configuration changes silently

["Daniel Urban (Jira)" <ji...@apache.org>]

Daniel Urban created KAFKA-15372:
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             Summary: MM2 rolling restart can drop configuration changes silently
                 Key: KAFKA-15372
                 URL: https://issues.apache.org/jira/browse/KAFKA-15372
             Project: Kafka
          Issue Type: Improvement
          Components: mirrormaker
            Reporter: Daniel Urban


When MM2 is restarted, it tries to update the Connector configuration in all flows. This is a one-time trial, and fails if the Connect worker is not the leader of the group.

In a distributed setup and with a rolling restart, it is possible that for a specific flow, the Connect worker of the just restarted MM2 instance is not the leader, meaning that Connector configurations can get dropped.

For example, assuming 2 MM2 instances, and one flow A->B:
 # MM2 instance 1 is restarted, the worker inside MM2 instance 2 becomes the leader of A->B Connect group.
 # MM2 instance 1 tries to update the Connector configurations, but fails (instance 2 has the leader, not instance 1)
 # MM2 instance 2 is restarted, leadership moves to worker in MM2 instance 1
 # MM2 instance 2 tries to update the Connector configurations, but fails

At this point, the configuration changes before the restart are never applied. Many times, this can also happen silently, without any indication.



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