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From Meng Zhu <m...@mesosphere.com>
Subject Re: New scheduler API proposal: unsuppress and clear_filter
Date Tue, 04 Dec 2018 21:46:32 GMT
Hi Benjamin:

Thanks for the great feedback.

I like the idea of giving frameworks more meaningful and fined grained
control over which filters to remove, especially this is likely to help
adoption. For example, letting the framework send an optional agentID which
instructs Mesos to only clear filters on that agent might help a task
launch with agent constraint.

However, when it comes to framework sent desired resource profiles, we
should give more thoughts. There is always the question that to what degree
do we support the various meta-data in the resource schema. I feel the
current schema is too complex for expressing resource needs, let alone
respecting it in the allocator (even just for the purpose of removing
filters). We probably want to first introduce a more concise format (such
as resourceQuantity) for all purposes of specifying desired resource
profiles (clear filters, quota guarantee, min_allocatable_resources and
etc) and start from there.

I suggest to just add the optional agentID atm and we can always add
support for specifying resource requirements in the future. And since its
semantic is far away from "requesting resources", I suggest keeping the
name of CLEAR(or REMOVE)_FILTERS.

What do you think?

-Meng

On Tue, Dec 4, 2018 at 1:50 AM Benjamin Bannier <
benjamin.bannier@mesosphere.io> wrote:

> Hi Meng,
>
> thanks for the proposal, I agree that the way these two aspects are
> currently entangled is an issue (e.g., for master/allocator performance
> reasons). At the same time, the workflow we currently expect frameworks to
> follow is conceptually not hard to grasp,
>
> (1) If framework has work then
> (i) put framework in unsuppressed state,
> (ii) decline not matching offers with a long filter duration.
> (2) If an offer matches, accept.
> (3) If there is no more work, suppress. GOTO (1).
>
> Here the framework does not need to track its filters across allocation
> cycles (they are an unexposed implementation detail of the hierarchical
> allocator anyway) which e.g., allows metaschedulers like Marathon or Apache
> Aurora to decouple the scheduling of different workloads. A downside of
> this interface is that
>
> * there is little incentive for frameworks to use SUPPRESS in addition to
> filters, and
> * unsupression is all-or-nothing, forcing the master to send potentially
> all unused resources to one framework, even if it is only interested in a
> fraction. This can cause, at least temporal, non-optimal allocation
> behavior.
>
> It seems to me that even though adding UNSUPPRESS and CLEAR_FILTERS would
> give frameworks more control, it would only be a small improvement. In
> above framework workflow we would allow a small improvement if the
> framework knows that a new workload matches a previously running workflow
> (i.e., it can infer that no filters for the resources it is interested in
> is active) so that it can issue UNSUPPRESS instead of CLEAR_FILTERS.
> Incidentally, there seems little local benefit for frameworks to use these
> new calls as they’d mostly help the master and I’d imagine we wouldn’t want
> to imply that clearing filters would unsuppress the framework. This seems
> too little to me, and we run the danger that frameworks would just always
> pair UNSUPPRESS and CLEAR_FILTERS (or keep using REVIVE) to simplify their
> workflow. If we’d model the interface more along framework needs, there
> would be clear benefit which would help adoption.
>
> A more interesting call for me would be REQUEST_RESOURCES. It maps very
> well onto framework needs (e.g., “I want to launch a task requiring these
> resources”), and clearly communicates a requirement to the master so that
> it e.g., doesn’t need to remove all filters for a framework. It also seems
> to fit the allocator model pretty well which doesn’t explicitly expose
> filters. I believe implementing it should not be too hard if we'd restrict
> its semantics to only communicate to the master that a framework _is
> interested in a certain resource_ without promising that the framework
> _will get them in any amount of time_ (i.e., no need to rethink DRF
> fairness semantics in the hierarchical allocator). I also feel that if we
> have REQUEST_RESOURCES we would have some freedom to perform further
> improvements around filters in the master/allocator (e.g., filter
> compatification, work around increasing the default filter duration, …).
>
>
> A possible zeroth implementation for REQUEST_RESOURCES with the
> hierarchical allocator would be to have it remove any filters containing
> the requested resource and likely to unsuppress the framework. A
> REQUEST_RESOURCES call would hold an optional resource and an optional
> AgentID; the case where both are empty would map onto CLEAR_FILTERS.
>
>
> That being said, it might still be useful to in the future expose a
> low-level knob for framework allowing them to explicitly manage their
> filters.
>
>
> Cheers,
>
> Benjamin
>
>
> On Dec 4, 2018, at 5:44 AM, Meng Zhu <mzhu@mesosphere.com> wrote:
> >
> > See my comments inline.
> >
> > On Mon, Dec 3, 2018 at 5:43 PM Vinod Kone <vinodkone@apache.org> wrote:
> >
> >> Thanks Meng for the explanation.
> >>
> >> I imagine most frameworks do not remember what stuff they filtered much
> >> less figure out how previously filtered stuff  can satisfy new
> operations.
> >> That sounds complicated!
> >>
> >
> > Frameworks do not need to remember what filters they currently have. Only
> > knowing
> > the resource profiles of the current vs. the previous operation would
> help
> > a lot.
> > But yeah, even this may be too much complexity.
> >
> >>
> >> But I like your example. So a suggestion we could make to frameworks
> could
> >> be to use CLEAR_FILTERS when they have new work, e.g., scale up/down,
> new
> >> app (they might want to use this even if they aren't suppressed!); and
> to
> >> use UNSUPPRESS when they are rescheduling old work?
> >>
> >
> > Yeah, these are the general guideline.
> >
> > I want to echo and reemphasize that CLEAR_FILTERS is orthogonal to
> > suppression.
> > Framework should consider clearing filters regardless of suppression.
> >
> > Ideally, when there is new different work, old irelavent filters should
> be
> > cleared. This helps
> > framework to get more offers and makes the allocator run faster (filter
> > could take up
> > bulk of the allocation time when they build up). On the flip side,
> calling
> > CLEAR_FILTERS too often
> > might also have performance implications (esp. if the master/allocator
> > actors are already stressed).
> >
> > Thoughts?
> >>
> >> On Mon, Dec 3, 2018 at 6:51 PM Meng Zhu <mzhu@mesosphere.com> wrote:
> >>
> >>> Hi Vinod:
> >>>
> >>> Yeah, `CLEAR_FILTERS` sounds good.
> >>>
> >>> UNSUPPRESS should be used whenever currently suppressed framework wants
> >> to
> >>> resume getting offers after a previous SUPPRESS call.
> >>>
> >>> As for `CLEAR_FILTERS`, the short (but not very useful) suggestion is
> to
> >>> call it whenever the framework wants to clear all the existing filters.
> >>>
> >>> To elaborate it, frameworks decline and accumulate filters when it is
> >>> trying to satisfy a particular set of requirements/constraints to
> perform
> >>> an operation. Once the operation is done and the next operation comes,
> if
> >>> the new operation has the same (or strictly more) resource
> >>> requirements/constraints compared to the last one, then it is more
> >>> efficient to KEEP the existing filters instead of getting useless
> offers
> >>> and rebuild the filters again.
> >>>
> >>> On the other hand, if the requirements/constraints are different (i.e.
> >> some
> >>> of the previous requirements could be loosened), then it means the
> >> existing
> >>> filter no longer make sense. Then it might be a good idea to clear all
> >> the
> >>> existing filters to improve the chance of getting more offers.
> >>>
> >>> Note, although we introduce `CLEAR_FILTERS` as part of decoupling the
> >>> `REVIVE` call, its usage should be independent of suppression/revival.
> >> The
> >>> decision to clear the filters only depends on whether the existing
> >> filters
> >>> make sense for the current operation constraints/requirements.
> >>>
> >>> Examples:
> >>> If a framework first launches a task, then wants to launch a
> replacement
> >>> task (because the first task failed), then it should keep the filters
> >> built
> >>> up during the first launch. However, if the framework wants to launch a
> >>> second task with a completely different resource profile, then clearing
> >>> filters might help to get more (otherwise filtered) offers and hence
> >> speed
> >>> up the deployment.
> >>>
> >>> -Meng
> >>>
> >>> On Mon, Dec 3, 2018 at 12:40 PM Vinod Kone <vinodkone@apache.org>
> wrote:
> >>>
> >>>> Hi Meng,
> >>>>
> >>>> What would be the recommendation for framework authors on when to use
> >>>> UNSUPPRESS vs CLEAR_FILTER?
> >>>>
> >>>> Also, should it CLEAR_FILTERS instead of CLEAR_FILTER?
> >>>>
> >>>> On Mon, Dec 3, 2018 at 2:26 PM Meng Zhu <mzhu@mesosphere.com>
wrote:
> >>>>
> >>>>> Hi:
> >>>>>
> >>>>> tl;dr: We are proposing to add two new V1 scheduler APIs: unsuppress
> >> and
> >>>>> clear_filter in order to decouple the dual-semantics of the current
> >>> revive
> >>>>> call.
> >>>>>
> >>>>> As pointed out in the Mesos framework scalability guide
> >>>>> <
> >>>
> >>
> http://mesos.apache.org/documentation/latest/app-framework-development-guide/#multi-scheduler-scalability
> >>>> ,
> >>>>> utilizing the suppress
> >>>>> <
> >>>
> >>
> http://mesos.apache.org/documentation/latest/scheduler-http-api/#suppress>
> >>>>> call is the key to get your cluster to a large number of frameworks
> >>>>> <
> >>>
> >>
> https://schd.ws/hosted_files/mesoscon18/84/Scaling%20Mesos%20to%20Thousands%20of%20Frameworks.pdf
> >>>> .
> >>>>> In short, when a framework is idling with no intention to launch
any
> >>> tasks,
> >>>>> it should suppress to inform the Mesos to stop sending any more
> >> offers.
> >>> And
> >>>>> the framework should revive
> >>>>> <
> >>>
> http://mesos.apache.org/documentation/latest/scheduler-http-api/#revive>
> >>>>> when new work arrives. This way, the allocator will skip the
> framework
> >>> when
> >>>>> performing resource allocations. As a result, thorny issues such
as
> >>> offer
> >>>>> starvation and resource fragmentation would be greatly mitigated.
> >>>>>
> >>>>> That being said. The suppress/revive calls currently are a little
bit
> >>>>> unwieldy due to MESOS-9028
> >>>>> <https://issues.apache.org/jira/browse/MESOS-9028>:
> >>>>>
> >>>>> The revive call has two semantics. It unsuppresses the framework
AND
> >>>>> clears all the existing filters. The later makes the revive call
> >>>>> non-idempotent. And sometimes users may want to keep the existing
> >>> filters
> >>>>> when reiving which is not possible atm.
> >>>>>
> >>>>> To decouple the semantics, as suggested in the ticket, we propose
to
> >> add
> >>>>> two new V1 scheduler calls:
> >>>>>
> >>>>> (1) `UNSUPPRESS` call requests the Mesos to resume sending offers;
> >>>>> (2) `CLEAR_FILTER` call will explicitly clear all the existing
> >> filters.
> >>>>>
> >>>>> To make life easier, both calls will return 200 OK (as opposed to
202
> >>>>> returned by most existing scheduler calls, including `SUPPRESS`
and
> >>>>> `REVIVE`).
> >>>>>
> >>>>> We will keep the revive call and its semantics (i.e. unsupppress
AND
> >>>>> clear filters) for backward compatibility.
> >>>>>
> >>>>> Note, the changes are proposed for V1 API only. Thus, once the
> changes
> >>>>> are landed, framework developers are encouraged to move to V1 API
to
> >>> take
> >>>>> advantage of the new calls (among many other benefits).
> >>>>>
> >>>>> Any feedback/comments are welcome.
> >>>>>
> >>>>> -Meng
> >>>>>
> >>>>
> >>>
> >>
>
>

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