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An Application Master (AM) is a per-application daemon to look after the lifecycle of the job.

The Application Master daemon is created when an application is started in the very first container.

The AM:

• communicates with YARN cluster
• handles application execution
• negotiate resources from the ResourceManager
• work with the NodeManager(s) to execute and monitor the tasks.

It has the responsibility to provide a web UI and to send that link to the RM.

During application launch time, the main tasks of the ApplicationMaster are:

• a) communicating with the ResourceManager to negotiate and allocate resources for future containers
• b) after container allocation, communicating YARN NodeManager's (NMs) to launch application containers on them.

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