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YARN Application

A YARN application consists of three components

Starting an application

The (YARN) client asks the resource manager to create a new application master instance.
The client tells the resource manager what the application master's physical resource requirements are.

Available applications

A fresh Hadoop installations comes with two applications:

Application ID

Influences the name for log files.
Finding ids of running(?) applications: 
yarn application -list
When an application is started, it will print something like 
16/06/19 20:42:07 INFO impl.YarnClientImpl: Submitted application application_1466361633780_0001
that helps determine the application id (here: application_1466361633780_0001).

See also

log files
Writing a YARN application

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