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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2179) HA: namenode fencing mechanism
Date Thu, 04 Aug 2011 02:57:27 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2179?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-2179:
------------------------------

    Attachment: hdfs-2179.txt

Thanks for the review. Here's a new revision:
- Added javadoc to FenceMethod, NodeFencer, etc
- Made FenceMethod a public interface, added audience/stability annotations
- Added a catch clause for all Throwables around each fence method
- Made SshFenceByTcpPort take a second parameter in order to configure the port of the target
process. eg <code>sshfence(nn2.foo.com, 8020)</code> will make it ssh into that
host and kill whatever process is listening on port 8020.

I imagine we'll need to revisit some of this when we're farther along in other areas -- in
particular so we can have the same configuration on the two peers, but have them properly
STONITH each other rather than themselves. But I think it's best to address that a little
down the road.


> HA: namenode fencing mechanism
> ------------------------------
>
>                 Key: HDFS-2179
>                 URL: https://issues.apache.org/jira/browse/HDFS-2179
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2179.txt, hdfs-2179.txt
>
>
> In an HA cluster, when there are two NNs, the invariant that only one NN is active at
a time has to be preserved in order to prevent "split brain syndrome." Thus, when a standby
NN is transition to "active" state during a failover, it needs to somehow _fence_ the formerly
active NN to ensure that it can no longer perform edits. This JIRA is to discuss and implement
NN fencing.

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