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https://issues.apache.org/jira/browse/KAFKA-21022?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ramu reassigned KAFKA-21022:
----------------------------

    Assignee: Ramu

> Broker Crash During ZK-to-KRaft Migration Due to Missing Topic ID in Empty 
> Log Directory
> ----------------------------------------------------------------------------------------
>
>                 Key: KAFKA-21022
>                 URL: https://issues.apache.org/jira/browse/KAFKA-21022
>             Project: Kafka
>          Issue Type: Bug
>          Components: kraft, migration
>    Affects Versions: 3.9.1
>            Reporter: Youssef Ismail
>            Assignee: Ramu
>            Priority: Critical
>
> While migrating a cluster from ZooKeeper to KRaft, during migration mode 
> brokers can crash after receiving a full {{LeaderAndIsr}} request from the 
> KRaft controller with the following error:
> {code:java}
> java.lang.RuntimeException: The log dir ... does not have a topic ID,{code}
>  
> During migration, Kafka checks the broker’s existing log directories through 
> {{{}findStrayReplicas{}}}. Unlike the normal KRaft startup path, this method 
> throws an exception when a topic ID is missing which is not allowed when 
> running in KRaft mode:
>  * [Migration path in 
> ReplicaManager|https://github.com/apache/kafka/blob/3.9/core/src/main/scala/kafka/server/ReplicaManager.scala#L1932-L1941]
>  * [Exception in 
> findStrayReplicas|https://github.com/apache/kafka/blob/3.9/core/src/main/scala/kafka/log/LogManager.scala#L1667-L1671]
> OSS addressed a similar problem in KAFKA-16814 and [PR 
> #16165|https://github.com/apache/kafka/pull/16165]. That fix treats a log 
> without a topic ID as stray during normal KRaft startup but the 
> migration-specific {{findStrayReplicas}} path still throws.
> I recovered by stopping the affected broker, removing the empty log 
> directory, and restarting it in migration mode.
> I propose updating {{findStrayReplicas}} to handle a missing topic ID the 
> same way as the normal KRaft path: treat the empty log as stray instead of 
> crashing the broker.



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