[openstack-dev] [nova][placement] Re: VMWare's resource pool / cluster and nested resource providers

Eric Fried openstack at fried.cc
Sat Jan 27 18:23:44 UTC 2018


    [+dev ML.  We're getting pretty general here; maybe others will get
some use out of this.]

> is there a way to make the scheduler allocate only from one specific RP

    "...one specific RP" - is that Resource Provider or Resource Pool?

    And are we talking about scheduling an instance to a specific
compute node, or are we talking about making sure that all the requested
resources are pulled from the same compute node (but it could be any one
of several compute nodes)?  Or justlimiting the scheduler to any node in
a specific resource pool?

    To make sure I'm fully grasping the VMWare-specific
ratios/relationships between resource pools and compute nodes,I have
been assuming:

controller 1:many compute "host"(where n-cpu runs)
compute "host"  1:many resource pool
resource pool 1:many compute "node" (where instances can be scheduled)
compute "node" 1:many instance

    (I don't know if this "host" vs"node" terminology is correct, but
I'm going to keep pretending it is for the purposes of this note.)

    In particular, if that last line is true, then you do *not* want
multiple compute "nodes" in the same provider tree.

> if no custom trait is specified in the request?

    I am not aware of anything current or planned that will allow you to
specify an aggregate you want to deploy from; so the only way I'm aware
of that you could pin a request to a resource pool is to create a custom
trait for that resource pool, tag all compute nodes in the pool with
that trait, and specify that trait in your flavor.  This way you don't
use nested-ness at all.  And in this model, there's also no need to
create resource providers corresponding to resource pools - their
solemanifestation is via traits.

    (Bonus: this model will work with what we've got merged in Queens -
we didn't quiiite finish the piece of NRP that makes them work for
allocation candidates, but we did merge trait support.  We're also
*mostly* there with aggregates, but I wouldn't want to rely on them
working perfectly and we're not claiming full support for them.)

    To be explicit, in the model I'm suggesting, your compute "host",
within update_provider_tree, would create new_root()s for each compute
"node".  So the "tree" isn't really a tree - it's a flat list of
computes, of which one happens to correspond to the `nodename` and
represents the compute "host".  (I assume deploys can happen to the
compute "host" just like they can to a compute "node"?  If not, just
give that guy no inventory and he'll be avoided.)  It would then
update_traits(node, ['CUSTOM_RPOOL_X']) for each.  It would also
update_inventory() for each as appropriate.

    Now on your deploys, to get scheduled to a particular resource pool,
you would have to specify required=CUSTOM_RPOOL_X in your flavor.

    That's it.  You never use new_child().  There are no providers
corresponding to pools.  There are no aggregates.

    Are we making progress, or am I confused/confusing?


On 01/27/2018 01:50 AM, Radoslav Gerganov wrote:
> +Chris
> Hi Eric,
> Thanks a lot for sending this.  I must admit that I am still trying to
> catch up with how the scheduler (will) work when there are nested RPs,
> traits, etc.  I thought mostly about the case when we use a custom
> trait to force allocations only from one resource pool.  However, if
> no trait is specified then we can end up in the situation that you
> describe (allocating different resources from different resource
> pools) and this is not what we want.  If we go with the model that you
> propose, is there a way to make the scheduler allocate only from one
> specific RP if no custom trait is specified in the request?
> Thanks,
> Rado
> ------------------------------------------------------------------------
> *From:* Eric Fried <openstack at fried.cc>
> *Sent:* Friday, January 26, 2018 10:20 PM
> *To:* Radoslav Gerganov
> *Cc:* Jay Pipes
> *Subject:* VMWare's resource pool / cluster and nested resource providers
> Rado-
>         It occurred to me just now that the model you described to me
> [1] isn't
> going to work, unless there's something I really misunderstood.
>         The problem is that the placement API will think it can allocate
> resources from anywhere in the tree for a given allocation request
> (unless you always use a single numbered request group [2] in your
> flavors, which doesn't sound like a clean plan).
>         So if you have *any* model where multiple compute nodes reside
> in the
> same provider tree, and I come along with a request for say
> VCPU:1,MEMORY_MB:2048,DISK_GB:512, placement will happily give you a
> candidate with the VCPU from compute10, the memory from compute5, and
> the disk from compute7.  I'm only guessing that this isn't a viable way
> to boot an instance.
>         I go back to my earlier suggestion: I think you need to create the
> compute nodes as root providers in your ProviderTree, and find some
> other way to mark the resource pool associations.  You could do it with
> custom traits (CUSTOM_RESOURCE_POOL_X, ..._Y, etc.); or you could do it
> with aggregates (an aggregate maps to a resource pool; associate all the
> compute providers in a given pool with its aggregate uuid).
>                         Thanks,
>                         Eric
> [1]
> http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2018-01-26.log.html#t2018-01-26T14:40:44
> [2]
> https://specs.openstack.org/openstack/nova-specs/specs/queens/approved/granular-resource-requests.html#numbered-request-groups

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