From Hadoop The Definitive Guide
The whole process is illustrated in Figure 7-1. At the highest level, there are five independent entities:
• The client, which submits the MapReduce job.
• The YARN resource manager, which coordinates the allocation of compute re‐ sources on the cluster.
• The YARN node managers, which launch and monitor the compute containers on machines in the cluster.
• The MapReduce application master, which coordinates the tasks running the Map‐ Reduce job. The application master and the MapReduce tasks run in containers that are scheduled by the resource manager and managed by the node managers.
What is the MapReduce application master?
In a MapReduce program written in Java, we need three things: a map function, a reduce function, and some code with
main() function to run the job. Is the MapReduce application master the code with
main() function to run a map reduce job?