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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8247) Auto-HA: add a config to enable auto-HA, which disables manual FC
Date Mon, 09 Apr 2012 22:55:18 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13250271#comment-13250271
] 

Todd Lipcon commented on HADOOP-8247:
-------------------------------------

Hi Hari. That's specifically the point of the FORCEMANUAL flag. It is not safe to use it with
automatic failover. So, the user has to accept the warning and acknowledge they're about to
do something dumb, that _will_ break auto failover if the ZKFCs are running.

The purpose of allowing it at all is to give a recourse for an expert admin if their ZK cluster
has crashed and they need to manually do a failover in an emergency situation. Its use is
highly discouraged. The warning printed is:
{code}
        "  --forceManual allows the manual failover commands to be used\n" +
        "                even when automatic failover is enabled. This\n" +
        "                flag is DANGEROUS and should only be used with\n" +
        "                expert guidance.");
{code}
                
> Auto-HA: add a config to enable auto-HA, which disables manual FC
> -----------------------------------------------------------------
>
>                 Key: HADOOP-8247
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8247
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: auto-failover, ha
>    Affects Versions: Auto Failover (HDFS-3042)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hadoop-8247.txt, hadoop-8247.txt
>
>
> Currently, if automatic failover is set up and running, and the user uses the "haadmin
-failover" command, he or she can end up putting the system in an inconsistent state, where
the state in ZK disagrees with the actual state of the world. To fix this, we should add a
config flag which is used to enable auto-HA. When this flag is set, we should disallow use
of the haadmin command to initiate failovers. We should refuse to run ZKFCs when the flag
is not set. Of course, this flag should be scoped by nameservice.

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