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https://issues.apache.org/jira/browse/KNOX-1414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16630797#comment-16630797
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Phil Zampino commented on KNOX-1414:
------------------------------------
[~kristopherkane] Are you certain that the DefaultHaDispatch is being used for
the NameNode requests? That dispatch _is_ configured for the DataNode requests
(though KNOX-1440 recently changed that), but all the NameNode requests should
involve the WebHdfsHaDispatch. Per KNOX-1440, DataNode requests will no longer
be retried when IOExceptions are encountered.
> DefaultHaDispatch is used by WEBHDFS instead of WebHdfsHaDispatch
> -----------------------------------------------------------------
>
> Key: KNOX-1414
> URL: https://issues.apache.org/jira/browse/KNOX-1414
> Project: Apache Knox
> Issue Type: Bug
> Affects Versions: 0.12.0
> Reporter: Kristopher Kane
> Priority: Minor
>
> Here is the series of failover attempts with DefaultHaDispatch (vs the
> WebHDFS one) when 403 is hit:
>
>
> {noformat}
> Caused by: java.io.IOException: java.io.IOException: Service connectivity
> error.
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.failoverRequest(DefaultHaDispatch.java:125)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.executeRequest(DefaultHaDispatch.java:94)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.failoverRequest(DefaultHaDispatch.java:119)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.executeRequest(DefaultHaDispatch.java:94)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.failoverRequest(DefaultHaDispatch.java:119)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.executeRequest(DefaultHaDispatch.java:94)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.failoverRequest(DefaultHaDispatch.java:119)
> at
> org.apache.hadoop.gateway.ha.dispatch.DefaultHaDispatch.executeRequest(DefaultHaDispatch.java:94)
> {noformat}
> But `data/services/webhdfs/2.4.0->service.xml` has:
>
> <dispatch
> classname="org.apache.hadoop.gateway.hdfs.dispatch.HdfsHttpClientDispatch"
> ha-classname="org.apache.hadoop.gateway.hdfs.dispatch.WebHdfsHaDispatch"/>
>
> Which should use WebHdfsHaDispatch.
>
> Both HA dispatch classes conduct HA failover/retry but WebHdfsHaDispatch is
> only slightly more context aware. Both could appear to work in 2/3rds of the
> cases (1/3rd being when the NN is in Safemode which is not handled
> specifically by the default dispatch) and you would not know
> WebHdfsHaDispatch was not being used unless you looked at gateway.log
>
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