Creating Job Labels

Explains the use of job labels to place jobs on particular nodes.

To place an individual job on a particular node, use a job label. You can apply job labels in three ways:

Use set() from the Hadoop configuration API in your Java application. For example:
```
conf.set("mapreduce.job.label","Production");
```

At the command line, pass the label in -Dmapreduce.job.label when you run the job with the hadoop jar command. For example:

hadoop jar /opt/mapr/hadoop/hadoop-2.4.1/share/hadoop/mapreduce/hadoop-mapreduce-examples-2.4.1-mapr-4.0.1-20140804.191359-4.jar \
teragen -Dmapreduce.job.label=Production 100000000 /teragen

Set the mapreduce.job.label parameter in mapred-site.xml. For example, to configure an application label expression for a MapReduce application that can run on any Development node or Fast node (including a Fast node from the Production rack), set the mapreduce.job.label parameter as shown:
```
<property>
   <name>mapreduce.job.label</name>
   <value>Development || Fast</value>
   <description>Label expression for MapReduce application</description>
</property>
```
Warning:
If an application is submitted with a label that does not correspond to any nodes, the application will run as though no label had been specified. Consult the ResourceManager log for more information (look for ‘invalid label’ error messages).