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https://issues.apache.org/jira/browse/OOZIE-1178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13559186#comment-13559186
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Bo Wang commented on OOZIE-1178:
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Hi Andrew,
bq. Would it be possible to refresh the patch on this JIRA?
The code is in an internal repo at Cloudera, but I am now back to school and
have no access to it.
{quote}
But for V2 and V3 when an AM is launched by the WF AM and not directly by the
RM the WF AM must take over some responsibilities of the RM. I am curious how
many of those responsibilities it will take over. I am also curious about what
modifications will be required to other AMs so that they can interact with both
the WF AM and also the RM directly.
bq. Would it be possible this could be handled by a RM<->AM delegation API,
with consideration for when the RM can kill a delegate not responding
sufficiently to its responsibilities?
{quote}
This is a good question. WfAM takes over responsibilities including monitoring
child AMs, killing/restarting child AMs in case of failure, etc. One of the
design principles is to allow AMs to run in WfAM without modification. In other
words, AMs should just treat WfAM as the "RM". Resource requests/releases
should all be sent to WfAM instead. Then WfAM will determine how to serve these
requests (either locally or forward it to RM).
When a WfAM is not responding (over a period long enough for restarting), RM
should kill the WfAM together with all the containers allocated to it. These
containers include child AMs and workers. When a child AM is not responding,
WfAM can trigger the kill and restart for it.
bq. Finally, it would be interesting and useful if something like the WFAM
proposed on this issue could maintain a persistent pool of workers...
Yes, maintaining a (relatively) persistent pool of workers can reduce the
scheduling cost. This is a great benefit of WfAM. Your comment reminds me of a
discussion on a RM<->WfAM protocol in one of the early design meetings. This
RM<->WfAM protocol allows RM to distinguish WfAM from other AMs. Thus each WfAM
can report to RM the idle resources it retains (for possible reallocations) via
this protocol. Then when there is a shortage of resources globally, RM can
request WfAMs to release withheld resources. This protocol is not included in
the proposal due to the potentially big changes to RM.
> Workflow Application Master in YARN
> -----------------------------------
>
> Key: OOZIE-1178
> URL: https://issues.apache.org/jira/browse/OOZIE-1178
> Project: Oozie
> Issue Type: New Feature
> Reporter: Bo Wang
> Attachments: MAPREDUCE-4495-v1.1.patch, MAPREDUCE-4495-v1.patch,
> MapReduceWorkflowAM.pdf, yapp_proposal.txt
>
>
> It is useful to have a workflow application master, which will be capable of
> running a DAG of jobs. The workflow client submits a DAG request to the AM
> and then the AM will manage the life cycle of this application in terms of
> requesting the needed resources from the RM, and starting, monitoring and
> retrying the application's individual tasks.
> Compared to running Oozie with the current MapReduce Application Master,
> these are some of the advantages:
> - Less number of consumed resources, since only one application master will
> be spawned for the whole workflow.
> - Reuse of resources, since the same resources can be used by multiple
> consecutive jobs in the workflow (no need to request/wait for resources for
> every individual job from the central RM).
> - More optimization opportunities in terms of collective resource requests.
> - Optimization opportunities in terms of rewriting and composing jobs in the
> workflow (e.g. pushing down Mappers).
> - This Application Master can be reused/extended by higher systems like Pig
> and hive to provide an optimized way of running their workflows.
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