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https://issues.apache.org/jira/browse/HDFS-14118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16774581#comment-16774581
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Fengnan Li commented on HDFS-14118:
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[~yzhangal] I added the answer in the modified hdfs-default.xml. Basically it
is for the case that DNS returns a fixed list of namenodes/routers since most
of the time the traffic will hit the DNS cache. DNS server itself does return
the list in random order (or order in permutation of all ips). By using random
it will avoid the client first hit the failed one consistently
> Use DNS to resolve Namenodes and Routers
> ----------------------------------------
>
> Key: HDFS-14118
> URL: https://issues.apache.org/jira/browse/HDFS-14118
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Fengnan Li
> Assignee: Fengnan Li
> Priority: Major
> Attachments: DNS testing log, HDFS design doc_ Single domain name for
> clients - Google Docs-1.pdf, HDFS design doc_ Single domain name for clients
> - Google Docs.pdf, HDFS-14118.001.patch, HDFS-14118.002.patch,
> HDFS-14118.003.patch, HDFS-14118.004.patch, HDFS-14118.005.patch,
> HDFS-14118.006.patch, HDFS-14118.007.patch, HDFS-14118.008.patch,
> HDFS-14118.009.patch, HDFS-14118.010.patch, HDFS-14118.011.patch,
> HDFS-14118.012.patch, HDFS-14118.013.patch, HDFS-14118.014.patch,
> HDFS-14118.015.patch, HDFS-14118.016.patch, HDFS-14118.017.patch,
> HDFS-14118.018.patch, HDFS-14118.019.patch, HDFS-14118.020.patch,
> HDFS-14118.patch
>
>
> Clients will need to know about routers to talk to the HDFS cluster
> (obviously), and having routers updating (adding/removing) will have to make
> every client change, which is a painful process.
> DNS can be used here to resolve the single domain name clients knows to a
> list of routers in the current config. However, DNS won't be able to consider
> only resolving to the working router based on certain health thresholds.
> There are some ways about how this can be solved. One way is to have a
> separate script to regularly check the status of the router and update the
> DNS records if a router fails the health thresholds. In this way, security
> might be carefully considered for this way. Another way is to have the client
> do the normal connecting/failover after they get the list of routers, which
> requires the change of current failover proxy provider.
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