Ticket for replace task primitive already exists: https://issues.apache.org/jira/browse/MESOS-1280
On Wed, Mar 8, 2017 at 6:34 PM, David McLaughlin <dmclaugh...@apache.org> wrote: > Spoke with Zameer offline and he asked me to post additional thoughts > here. > > My motivation for solving this without dynamic reservations is just the > sheer number of questions I have after reading the RFC and current design > doc. And most of them are not about the current proposal and goals or the > MVP but more about how this feature will scale into persistent storage. > > I think best-effort dynamic reservations are such a different problem than > the reservations that would be needed to support persistent storage. My > primary concern is around things like quota. For the current proposal and > the small best-effort feature we're adding, it makes no sense to get into > the complexities of separate quota for reserved resources vs preferred > resources, but the reality of exposing such a concept to a large > organisation where we can't automatically reclaim anything reserved means > we'd almost definitely want that. The issue with the iterative approach is > decisions we take here could have a huge impact on those tasks later, once > we expose the reserved tier into the open. That means more upfront design > and planning, which so far has blocked a super useful feature that I feel > all of us want. > > My gut feeling is we went about this all wrong. We started with dynamic > reservations and thought about how we could speed up task scheduling with > them. If we took the current problem brief and started from first > principals then I think we'd naturally look for something like a > replaceTask(offerId, taskInfo) type API from Mesos. > > I'll bring this up within our team and see if we can put resources on > adding such an API. Any feedback on this approach in the meantime is > welcome. > > On Wed, Mar 8, 2017 at 5:30 PM, David McLaughlin <dmclaugh...@apache.org> > wrote: > >> You don't have to store anything with my proposal. Preemption doesn't >> store anything either. The whole thing is it's just best-effort, and if the >> Scheduler restarts the worst that would happen is part of the current batch >> would have to go through the current Scheduling loop that users tolerate >> and deal with today. >> >> >> >> On Wed, Mar 8, 2017 at 5:08 PM, Zameer Manji <zma...@apache.org> wrote: >> >>> David, >>> >>> I have two concerns with that idea. First, it would require persisting >>> the >>> relationship of <Hostname, Resources> to <Task> for every task. I'm not >>> sure if adding more storage and storage operations is the ideal way of >>> solving this problem. Second, in a multi framework environment, a >>> framework >>> needs to use dynamic reservations otherwise the resources might be taken >>> by >>> another framework. >>> >>> On Wed, Mar 8, 2017 at 5:01 PM, David McLaughlin <dmclaugh...@apache.org >>> > >>> wrote: >>> >>> > So I read the docs again and I have one major question - do we even >>> need >>> > dynamic reservations for the current proposal? >>> > >>> > The current goal of the proposed work is to keep an offer on a host and >>> > prevent some other pending task from taking it before the next >>> scheduling >>> > round. This exact problem is solved in preemption and we could use a >>> > similar technique for reserving offers after killing tasks when going >>> > through the update loop. We wouldn't need to add tiers or >>> reconciliation or >>> > solve any of these other concerns. Reusing an offer skips so much of >>> the >>> > expensive stuff in the Scheduler that it would be a no-brainer for the >>> > operator to turn it on for every single task in the cluster. >>> > >>> > >>> > On Thu, Mar 2, 2017 at 7:52 AM, Steve Niemitz <sniem...@apache.org> >>> wrote: >>> > >>> > > I read over the docs, it looks like a good start. Personally I >>> don't see >>> > > much of a benefit for dynamically reserved cpu/mem, but I'm excited >>> about >>> > > the possibility of building off this for dynamically reserved >>> persistent >>> > > volumes. >>> > > >>> > > I would like to see more detail on how a reservation "times out", >>> and the >>> > > configuration options per job around that, as I feel like its the >>> most >>> > > complicated part of all of this. Ideally there would also be hooks >>> into >>> > > the host maintenance APIs here. >>> > > >>> > > I also didn't see any mention of it, but I believe mesos requires the >>> > > framework to reserve resources with a role. By default aurora runs >>> as >>> > the >>> > > special "*" role, does this mean aurora will need to have a role >>> > specified >>> > > now for this to work? Or does mesos allow reserving resources >>> without a >>> > > role? >>> > > >>> > > On Thu, Mar 2, 2017 at 8:35 AM, Erb, Stephan < >>> > stephan....@blue-yonder.com> >>> > > wrote: >>> > > >>> > > > Hi everyone, >>> > > > >>> > > > There have been two documents on Dynamic Reservations as a first >>> step >>> > > > towards persistent services: >>> > > > >>> > > > · RFC: https://docs.google.com/document/d/ >>> > > > 15n29HSQPXuFrnxZAgfVINTRP1Iv47_jfcstJNuMwr5A/edit#heading=h. >>> > hcsc8tda08vy >>> > > > >>> > > > · Technical Design Doc: https://docs.google.com/docume >>> nt/d/ >>> > > > 1L2EKEcKKBPmuxRviSUebyuqiNwaO-2hsITBjt3SgWvE/edit#heading=h. >>> > klg3urfbnq3v >>> > > > >>> > > > Since a couple of days there are also now two patches online for a >>> MVP >>> > by >>> > > > Dmitriy: >>> > > > >>> > > > · https://reviews.apache.org/r/56690/ >>> > > > >>> > > > · https://reviews.apache.org/r/56691/ >>> > > > >>> > > > From reading the documents, I am under the impression that there >>> is a >>> > > > rough consensus on the following points: >>> > > > >>> > > > · We want dynamic reservations. Our general goal is to >>> enable >>> > the >>> > > > re-scheduling of tasks on the same host they used in a previous >>> run. >>> > > > >>> > > > · Dynamic reservations are a best-effort feature. If in >>> doubt, >>> > a >>> > > > task will be scheduled somewhere else. >>> > > > >>> > > > · Jobs opt into reserved resources using an appropriate >>> tier >>> > > > config. >>> > > > >>> > > > · The tier config in supposed to be neither preemptible nor >>> > > > revocable. Reserving resources therefore requires appropriate >>> quota. >>> > > > >>> > > > · Aurora will tag reserved Mesos resources by adding the >>> unique >>> > > > instance key of the reserving task instance as a label. Only this >>> task >>> > > > instance will be allowed to use those tagged resources. >>> > > > >>> > > > I am unclear on the following general questions as there is >>> > contradicting >>> > > > content: >>> > > > >>> > > > a) How does the user interact with reservations? There are >>> > several >>> > > > proposals in the documents to auto-reserve on `aurora job create` >>> or >>> > > > `aurora cron schedule` and to automatically un-reserve on the >>> > appropriate >>> > > > reverse actions. But will we also allow a user further control >>> over the >>> > > > reservations so that they can manage those independent of the >>> task/job >>> > > > lifecycle? For example, how does Borg handle this? >>> > > > >>> > > > b) The implementation proposal and patches include an >>> > > > OfferReconciler, so this implies we don’t want to offer any >>> control for >>> > > the >>> > > > user. The only control mechanism will be the cluster-wide offer >>> wait >>> > time >>> > > > limiting the number of seconds unused reserved resources can linger >>> > > before >>> > > > they are un-reserved. >>> > > > >>> > > > c) Will we allow adhoc/cron jobs to reserve resources? Does >>> it >>> > even >>> > > > matter if we don’t give control to users and just rely on the >>> > > > OfferReconciler? >>> > > > >>> > > > >>> > > > I have a couple of questions on the MVP and some implementation >>> > details. >>> > > I >>> > > > will follow up with those in a separate mail. >>> > > > >>> > > > Thanks and best regards, >>> > > > Stephan >>> > > > >>> > > >>> > >>> > -- >>> > Zameer Manji >>> > >>> >> >> >
