Lucas Bradstreet created KAFKA-12896:
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Summary: Group rebalance loop caused by repeated group leader
JoinGroups
Key: KAFKA-12896
URL: https://issues.apache.org/jira/browse/KAFKA-12896
Project: Kafka
Issue Type: Bug
Components: clients
Affects Versions: 2.6.0
Reporter: Lucas Bradstreet
We encountered a strange case of a rebalance loop with the "cooperative-sticky"
assignor. The logs show the following for several hours:
{{Apr 7, 2021 @ 03:58:36.040 [GroupCoordinator 7]: Stabilized group mygroup
generation 19830137 (__consumer_offsets-7)}}
{{Apr 7, 2021 @ 03:58:35.992 [GroupCoordinator 7]: Preparing to rebalance
group mygroup in state PreparingRebalance with old generation 19830136
(__consumer_offsets-7) (reason: Updating metadata for member
mygroup-1-7ad27e07-3784-4588-97e1-d796a74d4ecc during CompletingRebalance)}}
{{Apr 7, 2021 @ 03:58:35.988 [GroupCoordinator 7]: Stabilized group mygroup
generation 19830136 (__consumer_offsets-7)}}
{{Apr 7, 2021 @ 03:58:35.972 [GroupCoordinator 7]: Preparing to rebalance
group mygroup in state PreparingRebalance with old generation 19830135
(__consumer_offsets-7) (reason: Updating metadata for member mygroup during
CompletingRebalance)}}
{{Apr 7, 2021 @ 03:58:35.965 [GroupCoordinator 7]: Stabilized group mygroup
generation 19830135 (__consumer_offsets-7)}}
{{Apr 7, 2021 @ 03:58:35.953 [GroupCoordinator 7]: Preparing to rebalance
group mygroup in state PreparingRebalance with old generation 19830134
(__consumer_offsets-7) (reason: Updating metadata for member
mygroup-7ad27e07-3784-4588-97e1-d796a74d4ecc during CompletingRebalance)}}
{{Apr 7, 2021 @ 03:58:35.941 [GroupCoordinator 7]: Stabilized group mygroup
generation 19830134 (__consumer_offsets-7)}}
{{Apr 7, 2021 @ 03:58:35.926 [GroupCoordinator 7]: Preparing to rebalance
group mygroup in state PreparingRebalance with old generation 19830133
(__consumer_offsets-7) (reason: Updating metadata for member mygroup during
CompletingRebalance)}}
Every single time, it was the same member that triggered the JoinGroup and it
was always the leader of the group.{{}}
The leader has the privilege of being able to trigger a rebalance by sending
`JoinGroup` even if its subscription metadata has not changed. But why would it
do so?
It is possible that this is due to the same issue or a similar bug to
https://issues.apache.org/jira/browse/KAFKA-12890.
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