Architecture

YARN Timeline Service v.2 uses a set of collectors (writers) to write data to the back-end
storage. The collectors are distributed and co-located with the application masters to which
they are dedicated. All data that belong to that application are sent to the application level
timeline collectors with the exception of the resource manager timeline collector.

For a given application, the application master can write data for the application to the co-located timeline collectors (which is an NM auxiliary service in this release). In addition,
node managers of other nodes that are running the containers for the application also write
data to the timeline collector on the node that is running the application master. 

The resource manager also maintains its own timeline collector. It emits only YARN-generic
life-cycle events to keep its volume of writes reasonable.

The timeline readers are separate daemons separate from the timeline collectors, and they
are dedicated to serving queries via REST API:

The following diagram illustrates the design at a high level: