What requests resources from YARN during a MapReduce job?ApplicationMasterApplicationsManagerMap and reduce tasksDataNodes

The ApplicationMaster is the component that requests resources from YARN during a MapReduce job. Here's a step-by-step explanation:

1. When a MapReduce job is submitted, the client first contacts the ResourceManager, which is the master daemon of YARN.

2. The ResourceManager then starts an ApplicationMaster for that job. The ApplicationMaster is a separate process that manages the lifecycle of the job and coordinates distributed execution.

3. The ApplicationMaster requests resources from the ResourceManager. These resources are in the form of containers, which are specific amounts of resource capacity on specific nodes.

4. Once the ApplicationMaster gets the necessary resources, it then communicates with the NodeManagers (slave daemons of YARN) on the allocated nodes to start the Map and Reduce tasks.

5. The Map and Reduce tasks process the data and the results are written back to the Hadoop Distributed File System (HDFS).

6. Once the job is completed, the ApplicationMaster deregisters with the ResourceManager and shuts down, returning its containers to the resource pool.

So, in summary, it's the ApplicationMaster that requests resources from YARN during a MapReduce job.