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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2179) HA: namenode fencing mechanism
Date Tue, 02 Aug 2011 00:40:28 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

Here's a preliminary version of this. I've included the basic framework code, as well as two
fencing implementations:
1) shell-command based fencing
2) ssh-based fencing that uses jsch to ssh into the target node and {{fuser}} to kill whatever
process is holding onto the target port

This isn't at all integrated into the NN as of yet, since it's not clear what the hook points
will be. But if this looks like the right path, I'd like to commit it to the HA branch, and
we can adapt it to its integration points (eg failover controller) later.

> 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
> 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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