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From "Chao Sun (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Deleted] (HDFS-14067) Allow manual failover between standby and observer
Date Tue, 13 Nov 2018 22:41:00 GMT

     [ https://issues.apache.org/jira/browse/HDFS-14067?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Chao Sun updated HDFS-14067:
    Comment: was deleted

(was: Thanks for the clarification [~xkrogen]. I think the check was introduced HADOOP-8247,
and the reason was because if we allow manual and auto failover at the same time, the state
tracked by ZK could be inconsistent with the actual state. For instance, in a HA cluster with
1 active and 1 standby, potentially one could manually transition the state of the NNs and
swap their roles, but the ZK will still track the old state.

In our case, we currently make the observer state a special case of standby state, so to ZK
they are the same. Therefore, I think allowing transition between observer and standby is
safe, without the check. There are still some doubts around this design though, such that
how we can make observer eligible for both manual and auto failover. This is tracked by HDFS-13182.)

> Allow manual failover between standby and observer
> --------------------------------------------------
>                 Key: HDFS-14067
>                 URL: https://issues.apache.org/jira/browse/HDFS-14067
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Chao Sun
>            Assignee: Chao Sun
>            Priority: Major
>         Attachments: HDFS-14067-HDFS-12943.000.patch
> Currently if automatic failover is enabled in a HA environment, transition from standby
to observer would be blocked:
> {code}
> [hdfs@*** hadoop-3.3.0-SNAPSHOT]$ bin/hdfs haadmin -transitionToObserver ha2
> Automatic failover is enabled for NameNode at ****
> Refusing to manually manage HA state, since it may cause
> a split-brain scenario or other incorrect state.
> If you are very sure you know what you are doing, please
> specify the --forcemanual flag.
> {code}
> We should allow manual transition between standby and observer in this case.

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