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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6371) In HA setup, the standby NN should redirect WebHDFS write requests to the active NN
Date Tue, 13 May 2014 13:39:16 GMT

    [ 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:
-----------------------------------

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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