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From "Bikas Saha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1584) Support explicit failover when automatic failover is enabled
Date Fri, 10 Jan 2014 20:03:50 GMT

    [ https://issues.apache.org/jira/browse/YARN-1584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13868231#comment-13868231

Bikas Saha commented on YARN-1584:

The duration of failover depends on how long ZK needs to figure out that the leader is gone.
Then notifying the new leader. Then new leader reading state.
Its not clear to me how any of these steps are faster with a admin failover option.

Not quite. When the RM is asked to transition to active via the AdminService (FORCE_USER)
flag, then the AdminService can transition to standby and then notify the elector to quitElection().
That API is present on the elector for this specific purpose. The elector gives up participation
in the leader election process. This RM will remain in standby (because the elector is not
going to notify it anymore) until the admin ask it to transitionToActive(FORCE_USER). Later,
when the AdminService is asked to transitionToActive() it can call the joinElection API on
the elector to rejoin the leader election and stay in the Standby state. The elector will
join the election and notify the RM to transitionToActive if it wins the election.

> Support explicit failover when automatic failover is enabled
> ------------------------------------------------------------
>                 Key: YARN-1584
>                 URL: https://issues.apache.org/jira/browse/YARN-1584
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: resourcemanager
>    Affects Versions: 2.4.0
>            Reporter: Karthik Kambatla
>            Assignee: Karthik Kambatla
> YARN-1029 adds automatic failover support. However, users can't explicitly ask for a
failover from one RM to the other without stopping the other RM. Stopping the RM until the
other RM takes over and then restarting the first RM is more involving and exposes the RM-ensemble
to SPOF for a longer duration. 
> It would be nice to allow explicit failover through yarn rmadmin -failover command.
> PS: HDFS supports -failover option. 

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