sanghyeok An created KAFKA-21212:
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Summary: Removed `client.rack` configuration is not reflected when
a Streams static member rejoins
Key: KAFKA-21212
URL: https://issues.apache.org/jira/browse/KAFKA-21212
Project: Kafka
Issue Type: Bug
Reporter: sanghyeok An
Assignee: sanghyeok An
*Description*
When a static member using {{group.protocol=streams}} restarts after removing
its {{client.rack}} configuration, the coordinator retains the previous rack ID.
During static member replacement, the coordinator copies the previous member’s
metadata and then treats {{RackId=null}} in the joining request as unchanged.
Changing the rack ID to another value works, but removing it does not.
*Conditions*
# Start a Streams application with {{group.instance.id}} and
{{{}client.rack=rack-a{}}}.
# Shut it down gracefully using the default close behavior.
# Remove the {{client.rack}} configuration.
# Restart with the same static instance ID before the session timeout expires.
*Expected behavior*
The coordinator should clear the rack ID to reflect the new client
configuration. Since the rack has changed, the group epoch should increase and
the assignment should be recomputed.
For regular heartbeats, {{RackId=null}} should continue to mean unchanged.
*Actual behavior*
The coordinator retains the previous rack ID. Group descriptions and custom
assignors therefore receive stale rack information, and rack removal itself
does not trigger assignment recomputation. If another metadata change triggers
recomputation, the stale rack information is still used.
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