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https://issues.apache.org/jira/browse/HADOOP-8210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13239494#comment-13239494
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Daryn Sharp commented on HADOOP-8210:
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I may not be properly understanding the intent of the change, hence my request
for clarification. I haven't fully researched the related jiras. I'll quickly
explain host based tokens so you can easily respond.
As you probably already know, the default token implementation always resolves
the host to an ip for the token's service. This is fine if the user explicitly
specified an ip (maybe due to dns errors, or no dns entries), but the host
based tokens preserve the exact hostname or ip the user specified. Preserving
the hostname shields the user against ip changes which is very important, for
example, when a local or remote NN's ip may change during an upgrade.
That said, will this change be used exclusively by the client to select an
outgoing network interface? That will be fine. My concern is if the client
starts always using ips for a remote host since the token will probably have to
contain the ip -- depending how/where these new methods are used. Resolving an
ip back to a hostname is insufficient since the user may have provided a CNAME
and a reverse lookup will return the A name. If the CNAME's ip changes, the
client will not detect it which defeats the host based tokens.
Thanks in advance for taking the time to explain.
> Common side of HDFS-3148
> ------------------------
>
> Key: HADOOP-8210
> URL: https://issues.apache.org/jira/browse/HADOOP-8210
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: io, performance
> Reporter: Eli Collins
> Assignee: Eli Collins
> Attachments: hadoop-8210.txt
>
>
> Common side of HDFS-3148, add necessary DNS and NetUtils methods. Test
> coverage is in the HDFS-3148 patch.
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