Do MR tasks talk to the JobHistoryServer directly (in MR2/Yarn) ? or only via MRAppMaster?

[Elkhan Dadashov <el...@gmail.com>]

Do MR tasks talk to the JobHistoryServer (in MR2/Yarn) ?

When and how MRDelegationToken is used ?

Do all Map and reduce tasks talk to JobHistoryServer (JHS) only via
MRAppMaster or they directly talk to JHS using MRDelegationToken ?

"The usage of JobHistoryServer during job submission is related to MR
Delegation Token renewal process. MRDelegationToken is issued by
JobHistoryServer to *delegate MR tasks talking to the JobHistoryServer*. "

Also on JavaDoc of MRDelegationTokenIdentifier it is said that : " {@link
TokenIdentifier} that identifies delegation tokens issued by
JobHistoryServer to delegate MR tasks talking to the JobHistoryServer."