Luke Chen created KAFKA-19850:
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Summary: KRaft voter auto join will add a removed voter immediately
Key: KAFKA-19850
URL: https://issues.apache.org/jira/browse/KAFKA-19850
Project: Kafka
Issue Type: Improvement
Affects Versions: 4.2.0
Reporter: Luke Chen
In v4.2.0, we have an auto join a controller with the configuration
`controller.quorum.auto.join.enable=true` set
([KIP-853|https://cwiki.apache.org/confluence/display/KAFKA/KIP-853%3A+KRaft+Controller+Membership+Changes#KIP853:KRaftControllerMembershipChanges-Controllerautojoining](KAFKA-19078)).
This is a good improvement for controller addition, but it has a minor issue,
which is that when a controller is removed via removeVoterRequest, it will be
added immediately due to `controller.quorum.auto.join.enable=true`. In the KIP,
we also mention you have to stop the controller before removing the controller:
{noformat}
controller.quorum.auto.join.enable:
Controls whether a KRaft controller should automatically join the cluster
metadata partition for its cluster id. If the configuration is set to
true the controller must be stopped before removing the controller with
kafka-metadata-quorum remove-controller.{noformat}
This is not a user friendly behavior in my opinion. And it will cause many
confusion to users and thought there is something wrong in the controller
removal. Furthermore, in the kubernetes environment which is controlled by the
operator, it is not the cloud native way to shutdown a node, do some operation,
then start it up.
So, I propose we can improve it by "the removed controller will not be auto
joined before this controller restarted". That is:
1. Once the controller is removed from voters set, it won't be auto joined even
if `controller.quorum.auto.join.enable=true`
2. The controller can be manually join the voters in this state
3. The controller node will be auto join the voters set after node restarted.
So basically, the semantics is not changed, it just add some unexpected
remove/add loop. Thoughts?
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