YARN was a module introduced in Hadoop 2. In Hadoop 1, the process of managing jobs and monitoring them was performed by processes known as JobTracker and TaskTracker(s). NameNodes that ran the JobTracker daemon (process) would submit jobs to the DataNodes which ran TaskTracker daemons (processes).
The JobTracker was responsible for the co-ordination of all MapReduce jobs and served as a central administrator for managing processes, handling server failure, re-allocating to new DataNodes, and so on. The TaskTracker monitored the execution of jobs local to its own instance in the DataNode and provided feedback on the status to the JobTracker as shown in the following:
JobTracker and TaskTrackers
This design worked well for a long ...
