Lianet Magrans created KAFKA-18095:
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Summary: Consider allowing member to join without subscription
under new consumer protocol
Key: KAFKA-18095
URL: https://issues.apache.org/jira/browse/KAFKA-18095
Project: Kafka
Issue Type: Improvement
Components: group-coordinator
Reporter: Lianet Magrans
Assignee: David Jacot
Fix For: 4.0.0
With the new consumer group protocol we currently enforce that members must
provide subscribed topics or a regex when joining the group. This prevents
members to join in cases where it subscribes to a java pattern for which the
client-side resolution finds no matching topics.
If we relax this validation, we would end up with a more consistent behaviour
for the regex subscriptions under the new protocol, given that currently, if
the regex is resolved on the broker and finds no matching topics, the member is
still allowed in the group (with no assignments), but if resolved on the client
it doesn't join.
Also, the consumer could continue to guarantee that it joins after
subscribe(Pattern), no matter if there are matching topics or not.
If we implement this change on the group coordinator, we also need to update
the new consumer to actually attempt to join after a call to subscribe(Pattern)
if no matching topics found (related jira)
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