MapReduce Job Failed in Multiple NameService Environment

Question

MapReduce or Yarn job fails in multiple nameService environment using viewFS.

Answer

When using viewFS only the mount directories are accessible, so the most possible cause is that the path configured is not in one of the mounted paths. For example:

<property>
<name>fs.defaultFS</name>
<value>viewfs://ClusterX/</value>
</property>
<property>
<name>fs.viewfs.mounttable.ClusterX.link./folder1</name>
<value>hdfs://NS1/folder1</value>
</property>
<property>
<name>fs.viewfs.mounttable.ClusterX.link./folder2</name>
<value>hdfs://NS2/folder2</value>
</property>

For all the MR properties which depends on HDFS, should use the paths inside mount folders.

Incorrect:

<property>
<name>yarn.app.mapreduce.am.staging-dir</name>
<value>/tmp/hadoop-yarn/staging</value>
</property>

As the root folder (/) is not accessible in viewFS.

Correct:

<property>
<name>yarn.app.mapreduce.am.staging-dir</name>
<value>/folder1/tmp/hadoop-yarn/staging</value>
</property>