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https://issues.apache.org/jira/browse/HADOOP-4016?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646318#action_12646318
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dhruba borthakur commented on HADOOP-4016:
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The way I understand this one:
Option1: When a JT machine fails, another machine can be brought up with the
same IP address as the original JT. The config files do not have to change, The
TaskTrackers have to start talking to the new machine using the old IP address.
Option2: Another way would be to start the a new instance of the JT on a
different machine that has a different IP address. The administrator can change
the entries in the hadoop config file. The TaskTrackers should be intelligent
enough to re-read the config file and then start talking to the new JT.
I guess Amar is trying out Option 1.
Option 2 has great advantagtes when the Hadoop administrator is not the same as
the DNS administrator. In my case, I can deploy Hadoop config files instantly,
where changing a DNS entry in a corporate-wide setting and waiting for the DNS
change to propagate takes a long long time.
> 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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