Junping Du commented on YARN-914:

Thanks [~vinodkv] for comments!
bq. IAC, I think we should also have a CLI command to decommission the node 
which optionally waits till the decommission succeeds.
That sounds pretty good. This new CLI can simply "gracefully" decommission 
related nodes and wait to timeout to forcefully decommission nodes haven't 
finished. Comparing with approach of external script proposed by Ming above, 
this has less dependency on effort that outside of hadoop.  

bq. Regarding storage of the decommission state, YARN-2567 also plans to make 
sure that the state of all nodes is maintained up to date on the state-store. 
That helps with many other cases too. We should combine these efforts.
That make sense. However, YARN-2567 is about threshold thing, may be a wrong 
JIRA number?

bq. Regarding long running services, I think it makes sense to let the admin 
initiating the decommission know - not in terms of policy but as a diagnostic. 
Other than waiting for a timeout, the admin may not have noticed that a service 
is running on this node before the decommission is triggered.

bq. This is the umbrella concern I have. There are two ways to do this: Let 
YARN manage the decommission process or manage it on top of YARN. If the later 
is the approach, I don't see a lot to be done here besides YARN-291. No?
Agree that there is less effort for 2nd approach. If so, we still need RM can 
aware containers/apps get finished then trigger shutdown to NM to make 
decommission comes earlier (and randomly) which I guess is important to upgrade 
of large cluster. Isn't it? For YARN-291, my understanding is now we don't rely 
on any open issues left there because we only need to set NM's resource to 0 at 
runtime which we already provide there. BTW, I think the approach you just 
proposed above is "2nd approach + a new CLI". Isn't it? I prefer to go with 
this way but would like to hear other guys' ideas here also.

> Support graceful decommission of nodemanager
> --------------------------------------------
>                 Key: YARN-914
>                 URL: https://issues.apache.org/jira/browse/YARN-914
>             Project: Hadoop YARN
>          Issue Type: Improvement
>    Affects Versions: 2.0.4-alpha
>            Reporter: Luke Lu
>            Assignee: Junping Du
>         Attachments: Gracefully Decommission of NodeManager (v1).pdf
> When NMs are decommissioned for non-fault reasons (capacity change etc.), 
> it's desirable to minimize the impact to running applications.
> Currently if a NM is decommissioned, all running containers on the NM need to 
> be rescheduled on other NMs. Further more, for finished map tasks, if their 
> map output are not fetched by the reducers of the job, these map tasks will 
> need to be rerun as well.
> We propose to introduce a mechanism to optionally gracefully decommission a 
> node manager.

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