Using Node Labels to Schedule YARN Applications

To set up node labels for the purpose of scheduling YARN applications (including MapReduce applications) on a specific node or group of nodes:

Create a text file and specify the labels you want to use for the nodes in your cluster. In this example, the file is named node.labels.
Copy the file to a location on MapR file system where it will not be modified or deleted, such as /var/mapr.
```
hadoop fs -put ~/node.labels /var/mapr
```

Edit yarn-site.xml on all ResourceManager nodes and set the node.labels.file parameter and the optional node.labels.monitor.interval parameter as shown:

<property>
   <name>node.labels.file</name>
   <value>/var/mapr/node.labels</value>
   <description>The path to the node labels file.</description>
</property>

<property>
   <name>node.labels.monitor.interval</name>
   <value>120000</value>
   <description>Interval for checking the labels file for updates (default is 120000 ms)</description>
</property>

Restart ResourceManager to set up the labels from the node labels file for the first time. For this and subsequent changes to take effect, issue either of the following commands to manually tell the ResourceManager to reload the node labels file:
- For any YARN applications, including MapReduce applications, enter yarn rmadmin -refreshLabels
- For MapReduce applications, enter mapred job -refreshLabels
Verify that labels are implemented correctly by running either of the following commands:
```
yarn rmadmin -showLabels
mapred job -showLabels 
```

The following flowchart summarizes these steps. In addition, the flowchart introduces the concept of queue labels for the Fair Scheduler and the Capacity Scheduler.