[jira] [Resolved] (KAFKA-19148) Potential Unclean Leader Election in KRaft Despite unclean.leader.election.enable=false

["Julian Bergner (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-19148?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Bergner resolved KAFKA-19148.
------------------------------------
    Fix Version/s: 4.1.0
       Resolution: Fixed

> Potential Unclean Leader Election in KRaft Despite unclean.leader.election.enable=false
> ---------------------------------------------------------------------------------------
>
>                 Key: KAFKA-19148
>                 URL: https://issues.apache.org/jira/browse/KAFKA-19148
>             Project: Kafka
>          Issue Type: Bug
>          Components: controller
>    Affects Versions: 3.9.0, 4.0.0
>            Reporter: Julian Bergner
>            Assignee: Julian Bergner
>            Priority: Critical
>             Fix For: 4.1.0
>
>         Attachments: Readme_Kraft.md, Readme_Zookeeper.md, docker-compose_kraft.yml, docker-compose_zookeeper.yml
>
>
> *Issue Summary:*
> We're observing unclean leader election even though {{{}unclean.leader.election.enable=false{}}}.
> *Scenario:*
> During a partition reassignment, if we promote a non-ISR broker to leader and simultaneously remove the current leader from the ISR, Kafka still elects a new leader from outside the ISR. This behavior contradicts the expected behavior when unclean leader election is explicitly disabled.
> *Details:*
>  * *Original ISR:* [1, 2]
>  * *New ISR after reassignment:* [3, 2]
> *Kafka Versions Tested:*
>  * Kafka 4.0.0 (KRaft mode)
>  * Kafka 3.9.0 (Kraft mode)
>  * Kafka 3.9.0 (Zookeeper mode)
> *Observation:*
>  * The behaviour differs between the two modes.
>  * In Kraft, unclean leader election occurred, which should not happen with the config set to {{{}false{}}}.
>  * In Zookeeper no unclean leader election occurred.
> *Attachments:*
> Docker Compose files and reproduction steps for both:
>  * Kafka 4.0.0 (KRaft)
>  * Kafka 3.9.0 (Zookeeper)



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