Latest news on what's going on with resource providers and the placement API. I've made some adjustments in the structure of this since last time[0]. The new structure tries to put the stuff we need to talk about, including medium and long term planning, at the top and move the stuff that is summaries of what's going on on gerrit towards the bottom. I think we need to do this to enhance the opportunities for asynchronous resolution of some of the topics on our plates. If we keep waiting until the next meeting where we are all there at the same time, stuff will sit for too long. [0] http://lists.openstack.org/pipermail/openstack-dev/2016-November/107982.html # Things to Think About (Note that I'm frequently going to be wrong or at least incomplete about the things I say here, because I'm writing off the top of my head. Half the point of writing this is to get it correct by collaborative action. If you see something that is wrong, please shout out in a response. This section is for discussion of stuff that isn't yet being tracked well or has vague conflicts.) The general goal with placement for Ocata is to have both the nova scheduler and resource tracker talking to the API to usefully limit the number of hosts that the scheduler evaluates when selecting destinations. There are several segments of work coming together to make this possible, some of which are further along than others. ## Update Client Side to Consider Aggregates When the scheduler requests a list of resource providers, that list ought to include compute nodes that are are associated, via aggregates, with any shared resource provides (such as shared disk) that can satisfy the resource requirements in the request. Meanwhile, when a compute node places a VM that uses shared disk the allocation of resources made by the resource tracker need to go to the right resource providers. This is a thing we know we need to do but is not something for which (as far as I know) we've articulated a clear plan or really started on. ## Update Scheduler to Request Limited Resource Providers The "Scheduler Filters in DB" spec[1] has merged along with its pair, "Filter Resource Providers by Request"[2], and the work has started[3]. There are some things to consider as that work progresses: * The bit about aggregates in the previous section: the list of returned resource providers needs to include associated providers. To quote Mr. Pipes: we will only return resource providers to the scheduler that are compute nodes in Ocata. the resource providers that the placement service returns will either have the resources requested or will be associated with aggregates that have providers that match the requested resources. * There is unresolved debate about the structure of the request being made to the API. Is it POST or a GET, does it have a body or use query strings? The plan is to resolve this discussion in the review of the code at [3]. [1] http://specs.openstack.org/openstack/nova-specs/specs/ocata/approved/resource-providers-scheduler-db-filters.html [2] http://specs.openstack.org/openstack/nova-specs/specs/ocata/approved/resource-providers-get-by-request.html [3] https://review.openstack.org/#/c/386242/ ## Docs In addition to needing an api-ref we also need a placement-dev.rst to go alongside the placement.rst. The -dev would mostly explain the how and the why of the placement API archicture, how the testing works, etc. That's mostly on me. ## Placement Upgrade/Installation issues (This is a straight copy from the previous message) In his response[4] to this topic Matt R pointed out todos for this topic: * get the placement-api enabled by default in the various bits ofocata CI * ensure that microversions are being used on both sides of the
placement API transactions (that's true in pending changes to both the API and the resource tracker) [4] http://lists.openstack.org/pipermail/openstack-dev/2016-November/107177.html ## Long Term Stuff ### Making Claims in the Placement API After Ocata the placement API will evolve to make claims, on the /allocations endpoint. When presented with a set of resources requirements _the_ resource provider that satisfies those requiements will be returned and the claim of resources made in a single step. To quote Mr. Pipes again: once we have a placement service actually doing claims, the returned resource providers for an allocation will be the actual resource providers that were allocated against (which include *both* compute node providers as well as any resource provider of a shared resource that was allocated) Just so folk are aware. ### Moving Placement out of Nova If this is something we ever plan to do (there appear to be multiple points of view) then it is something we need to prepare for to ease the eventual transition. Some of these things include: * Removing as much 'nova.*' packages from the hierarchy of placement modules. * Getting the new placement DB[5][6] handled in some way * Removing remotable from the resource provider objects. The intent is that these will never be accessed other than through the HTTP API and since that scales horizontally, no RPC should be required. If we ever plan to remove it, sooner is better than later. A POC has been submitted[7], but there's disagreement about whether we should do it. We need to resolve that. [5] https://review.openstack.org/#/c/362766/ [6] https://etherpad.openstack.org/p/placement-optional-db-spec [7] https://review.openstack.org/#/c/404279/ # Pending Planned Work ## Custom Resource Classes Jay just posted a big update[8] on that so go look at that. A lot of code has merged, but a lot of code[9] is still in flight. [8] http://lists.openstack.org/pipermail/openstack-dev/2016-December/108393.html [9] https://review.openstack.org/#/q/topic:bp/custom-resource-classes ## Filtering compute nodes with the placement API Already mentioned (with links) above. ## Nested Resource Providers In discussions yesterday about Ocata priorities[10] we clarified that while resource providers matter, they are a stretch for Ocata. The primary goal is to have enough discussion and experimentation now so that we can have useful discussions at the PTG. The spec[11] has merged, the code is in a stack[12]. There's general agreement on the implementation, but there still seems to be some concern about how it is all going to work and what it all means in actual practice. The expectation is that we'll figure things when we're doing that actual practice. [10] https://review.openstack.org/#/c/404456/ [11] http://specs.openstack.org/openstack/nova-specs/specs/ocata/approved/nested-resource-providers.html [12] https://review.openstack.org/#/c/377138/ ## Allocations for generic PCI devices This code was abandoned because it was making some bad assumptions about how PCI device handling is done. See the abandoned review[13] for more information. [13] https://review.openstack.org/#/c/374681/ # Pending Pickup Work (Bugs[14], stuff from the leftovers etherpad[15], other random bits of improvement.) [14] https://bugs.launchpad.net/nova/+bugs?field.tag=placement [15] https://etherpad.openstack.org/p/placement-newton-leftovers * Demo inventory update script: https://review.openstack.org/#/c/382613/ This one might be considered a WIP because how it chooses to do things (rather simply and dumbly) may not be in line with expecations. * CORS support in placement API: https://review.openstack.org/#/c/392891/ John Garbutt's review led to finding a huge bug in this (service wouldn't start in an actual deployment). That's been fixed. * Handling limits in schema better https://review.openstack.org/#/c/399002/ (needs review) https://review.openstack.org/#/c/398998/ (needs fixes from submitter) * [WIP] Placement api: Add json_error_formatter to defaults https://review.openstack.org/#/c/395194/ This is an effort to avoid boilerplate, but no good solution has been determined yet. Reviewers can help us figure a good way to hande things. * Small improvements to placement.rst https://review.openstack.org/#/c/403811/ # End As usual, I hope this is useful to people. If something is missing or incorrect please say so. It's quite a bit of work to assemble this, but it's useful to me, so I'd be doing it anyway, even if I wasn't sending it out. I hope other people find it useful. If there's something I can do to make it more useful, let me know. -- Chris Dent ¯\_(ツ)_/¯ https://anticdent.org/ freenode: cdent tw: @anticdent
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