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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4016) TaskTrackers never (re)connect back to the JobTracker if the JobTracker node/machine is changed
Date Mon, 10 Nov 2008 14:43:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4016?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646272#action_12646272
] 

Amar Kamat commented on HADOOP-4016:
------------------------------------

@Dhruba I changed the entry in _/etc/hosts_ to point to the ip address of the new JobTracker.
The idea was to check if task-tracker ever tries to re-resolve the jobtracker's hostname.
@Steve I think we should force a hostname->ip-address resolution after few retries. So
that a simple DNS entry change and a jobtracker restart would be enough to recover from a
failure. Either we could make the JVM do it or we can manually do it by keeping tracker of
how many times we reconnect. I think doing it manually makes sense as we can control when
the resolution happens.

> TaskTrackers never (re)connect back to the JobTracker if the JobTracker node/machine
is changed
> -----------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4016
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4016
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Amar Kamat
>
> I tried the following 
> 1) Started a hadoop cluster.
> 2) Killed the JT
> 3) Selected a new node for starting JT. 
> 4) Changed the entry on the tasktracker to reflect the new (old) hostname to (new) ip
mapping. Checked if the tracker node correctly resolves the hostname to the new ip.
> 5) Start the JT on the new node
> The tasktracker fails to connect to the new jobtracker. It seems that the hostname resolution
remains stale and is never updated.

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