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https://issues.apache.org/jira/browse/HDFS-6371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13996394#comment-13996394
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Daryn Sharp commented on HDFS-6371:
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Agreed on client side retries. With IP-based failover, a standby NN that
attempts to redirect to the other NN will create a redirect loop to itself
until the IP failover to the active occurs.
> In HA setup, the standby NN should redirect WebHDFS write requests to the
> active NN
> -----------------------------------------------------------------------------------
>
> Key: HDFS-6371
> URL: https://issues.apache.org/jira/browse/HDFS-6371
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode, webhdfs
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
>
> The current WebHDFS implementation in namenode does not check its HA state --
> it does the same thing no matter it is active or standby.
> Suppose a http client talk to the standby NN via WebHDFS. For the read
> operations, there is no problem. For the write operations, if the operation
> requires http redirect (e.g. creating a file), it will work since the standby
> NN will also redirect the client to a DN. When the client connect to the DN,
> the DN will fulfill the request with the active NN. However, for the write
> operations not requiring http redirect (e.g. mkdir), the operation will fail
> with StandbyException since it will be executed with the standby NN.
> There are two solutions:
> # The http client could catch StandbyException and then retries with the
> other NN in this case.
> # The standby NN redirects the request to the active NN.
> The second solution seems better since the client does not need to know both
> active NN and standby NN.
> Note that WebHdfsFileSystem is already able to handle HA failover. The JIRA
> is for other http clients.
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