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https://issues.apache.org/jira/browse/MAPREDUCE-5751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13900752#comment-13900752
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Gera Shegalov commented on MAPREDUCE-5751:
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I think you can easily add a test case to TestMRAppMaster
> MR app master fails to start in some cases if mapreduce.job.classloader is
> true
> -------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5751
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5751
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 2.2.0
> Reporter: Sangjin Lee
> Assignee: Sangjin Lee
> Attachments: mapreduce-5751.patch
>
>
> If mapreduce.job.classloader is set to true, and the MR client includes a
> jetty jar in its libjars or job jar, the MR app master fails to start. A
> typical stack trace we get is as follows:
> {noformat}
> java.lang.ClassCastException: org.mortbay.jetty.webapp.WebInfConfiguration
> cannot be cast to org.mortbay.jetty.webapp.Configuration
> at
> org.mortbay.jetty.webapp.WebAppContext.loadConfigurations(WebAppContext.java:890)
> at
> org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:462)
> at
> org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
> at
> org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
> at
> org.mortbay.jetty.handler.ContextHandlerCollection.doStart(ContextHandlerCollection.java:156)
> at
> org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
> at
> org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
> at org.mortbay.jetty.Server.doStart(Server.java:224)
> at
> org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
> at org.apache.hadoop.http.HttpServer.start(HttpServer.java:676)
> at org.apache.hadoop.yarn.webapp.WebApps$Builder.start(WebApps.java:208)
> at
> org.apache.hadoop.mapreduce.v2.app.client.MRClientService.start(MRClientService.java:151)
> at
> org.apache.hadoop.yarn.service.CompositeService.start(CompositeService.java:68)
> at
> org.apache.hadoop.mapreduce.v2.app.MRAppMaster.start(MRAppMaster.java:1040)
> at
> org.apache.hadoop.mapreduce.v2.app.MRAppMaster$1.run(MRAppMaster.java:1307)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:415)
> at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1478)
> at
> org.apache.hadoop.mapreduce.v2.app.MRAppMaster.initAndStartAppMaster(MRAppMaster.java:1303)
> at
> org.apache.hadoop.mapreduce.v2.app.MRAppMaster.main(MRAppMaster.java:1259)
> {noformat}
> This happens because as part of the MR app master start the jetty classes are
> loaded normally through the app classloader, but WebAppContext tries to load
> the specific Configuration class via the thread context classloader (which
> had been set to the user job classloader).
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