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https://issues.apache.org/jira/browse/HADOOP-4016?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646529#action_12646529
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Steve Loughran commented on HADOOP-4016:
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Dhruba, I think you've got same-IP and same hostname mixed up. Same IP is easy,
only the routers care
Same hostname, different IP means you have to wait for DNS entries to propagate
around. Some places it works, some places it doesnt.
Changing the configuration works on top of changing the hostname, as it doesn't
prevent you doing that, but you can try other things like bringing up a new JT
on a different port on the same box, new machine, etc. But you do need a way to
push out configuration changes to all the task trackers, which classic
XML-driven configurations don't have. I can do it, but my code to do that is
from subclassing JobConf and using SmartFrog. HADOOP-3582 is a todo list of
better configuration options; you'd need a way to push out the change.
1. the extra cost of another lookup of the configuration file is minimal if you
are doing retries anyway.
2. we should set the dns TTL anyway too, but check with Allen what settings he
likes before bringing the network down.
3. configuration file changes are easier to test, so we can see that the file
gets checked.
> 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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