Gergo Repas updated YARN-7913:
    Attachment: YARN-7913.000.poc.patch

> Improve error handling when application recovery fails with exception
> ---------------------------------------------------------------------
>                 Key: YARN-7913
>                 URL: https://issues.apache.org/jira/browse/YARN-7913
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: resourcemanager
>    Affects Versions: 3.0.0
>            Reporter: Gergo Repas
>            Assignee: Gergo Repas
>            Priority: Major
>         Attachments: YARN-7913.000.poc.patch
> There are edge cases when the application recovery fails with an exception.
> Example failure scenario:
>  * setup: a queue is a leaf queue in the primary RM's config and the same 
> queue is a parent queue in the secondary RM's config.
>  * When failover happens with this setup, the recovery will fail for 
> applications on this queue, and an APP_REJECTED event will be dispatched to 
> the async dispatcher. On the same thread (that handles the recovery), a 
> NullPointerException is thrown when the applicationAttempt is tried to be 
> recovered 
> (https://github.com/apache/hadoop/blob/55066cc53dc22b68f9ca55a0029741d6c846be0a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java#L494).
>  I don't see a good way to avoid the NPE in this scenario, because when the 
> NPE occurs the APP_REJECTED has not been processed yet, and we don't know 
> that the application recovery failed.
> Currently the first exception will abort the recovery, and if there are X 
> applications, there will be ~X passive -> active RM transition attempts - the 
> passive -> active RM transition will only succeed when the last APP_REJECTED 
> event is processed on the async dispatcher thread.
> _The point of this ticket is to improve the error handling and reduce the 
> number of passive -> active RM transition attempts (solving the above 
> described failure scenario isn't in scope)._

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