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 data-fabric filesystem 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>

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.