[jira] [Commented] (YARN-1200) Provide a central view for rack topologies

["Steve Loughran (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-1200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13767406#comment-13767406 ] 

Steve Loughran commented on YARN-1200:
--------------------------------------

+1 to this idea -without it AMs can't track topologies that change over time.

This should include
# failure domain topology
# time last updated

Having a timestamp will let the AMs decide whether or not to rebuild their local datastructures when querying the rack.

Actually, having a notification that the topology has changed could be even more useful for some applications, but that is very much feature creep.
                
> Provide a central view for rack topologies
> ------------------------------------------
>
>                 Key: YARN-1200
>                 URL: https://issues.apache.org/jira/browse/YARN-1200
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: resourcemanager
>    Affects Versions: 2.1.0-beta
>            Reporter: Harsh J
>
> It appears that with YARN, any AM (such as the MRv2 AM) that tries to do rack-info-based work, will need to resolve racks locally rather than get rack info from YARN directly: https://github.com/apache/hadoop-common/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/rm/RMContainerAllocator.java#L1054 and its use of a simple implementation of https://github.com/apache/hadoop-common/blob/trunk/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/util/RackResolver.java
> This is a regression, as we've traditionally only had users maintain rack mappings and its associated script on a single master role node (JobTracker), not at every compute node. Task spawning hosts have never done/needed rack resolution of their own.
> It is silly to have to maintain rack configs and their changes on all nodes. We should have the RM host a stable interface service so that there's only a single view of the topology across the cluster, and document for AMs to use that instead.

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