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https://issues.apache.org/jira/browse/MAPREDUCE-5576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13794730#comment-13794730
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Karthik Kambatla commented on MAPREDUCE-5576:
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Thanks [~zjshen] for the clarification. Read the description again, and I
understand the intent now. May be, changing the summary might help make it
easier to understand.
> MR AM unregistration should be failed due to UnknownHostException on getting
> history url
> ----------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5576
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5576
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Zhijie Shen
> Assignee: Zhijie Shen
>
> Before RMCommunicator sends the request to RM to finish the application, it
> will try to get the JHS url, which may throw UnknownHostException. The
> current code path will skip sending the request to RM when the exception is
> raised, which sounds not a reasonable behavior, because RM's unregistering an
> AM will not affected by the tracking URL. The URL can be empty or null.
> AFAIK, the impact of null URL will be that the URL to redirect users from RM
> web page to JHS will be unavailable, and the job report will not show the URL
> as well. However, is it much much better than failing an application because
> of UnknownHostException here? Anyway, users can go to JHS directly to find
> the application history info.
> Therefore, the reasonable code path here should be catching
> UnknownHostException and set historyUrl = null
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