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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