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[nova] Strict isolation of group of hosts for image and flavor, modifying command 'nova-manage placement sync_aggregates'


On Fri, 2019-06-07 at 19:04 +0100, Sean Mooney wrote:
> On Fri, 2019-06-07 at 09:05 -0500, Eric Fried wrote:
> > > > > (a) Leave all traits alone. If they need to be removed, it would have to
> > > > > be manually via a separate step.
> > > > > 
> > > > > (b) Support a new option so the caller can dictate whether the operation
> > > > > should remove the traits. (This is all-or-none.)
> > > > > 
> > > > > (c) Define a "namespace" - a trait substring - and remove only traits in
> > > > > that namespace.
> > > > 
> > > > I'm going to -1 (b). It's too big a hammer, at too big a cost (including
> > > > API changes).
> > > > 
> > > > > If Iâ??m not wrong, for last two approaches, we would need to change
> > > > > RestFul APIs.
> > > > 
> > > > No, (c) does not. By "define a namespace" I mean we would establish a
> > > > naming convention for traits to be used with this feature. For example:
> > > > 
> > > > CUSTOM_AGGREGATE_ISOLATION_WINDOWS_LICENSE
> > > 
> > > i personaly dislike c as it means we cannot use any standard traits in host
> > > aggrates.
> > 
> > Actually, it means we *can*, whereas (b) and (d) mean we *can't*. That's
> > the whole point. If we want to isolate our hyperthreading hosts, we put
> > them in an aggregate with HW_CPU_HYPERTHREADING on it. The sync here
> > should be a no-op because those hosts should already have
> > HW_CPU_HYPERTHREADING on them. And then if we decide to remove such a
> > host, or destroy the aggregate, or whatever, we *don't want*
> > HW_CPU_HYPERTHREADING to be removed from the providers, because they can
> > still do that.
> 
> in the cpu pinning spec we said HW_CPU_HYPERTHREADING was not going to be managed
> by the virt driver so it wont be reported unless the admin manulaly adds it.
> 
> 
https://github.com/openstack/nova-specs/blob/master/specs/train/approved/cpu-resources.rst#add-hw_cpu_hyperthreading-trait
> "The HW_CPU_HYPERTHREADING trait will need to be among the traits that the virt driver cannot always override, since
> the
> operator may want to indicate that a single NUMA node on a multi-NUMA-node host is meant for guests that tolerate
> hyperthread siblings as dedicated CPUs."
> 
> so i was suggesting this was a way to enable that the operator to manage whic host report that trait
> although as the spec suggest we may  want to report this differently per numa node which would still
> require you to use osc-placment or some other way to set it manually.
> > 
> > (Unless you mean we can't make a standard trait that we can use for
> > isolation that gets (conditionally) removed in these scenarios? There's
> > nothing preventing us from creating a standard trait called
> > COMPUTE_AGGREGATE_ISOLATION_WINDOWS_LICENSE, which would work just the
> > same.)
> 
> im suggesting it woudl be nice to be able to use host aggates to manage statdard or custom traits on hosts that are
> not managed by the driver thwer ethat is a COMPUTE_AGGREGATE_ISOLATION_WINDOWS_LICENSE trait or something
> else. so i was hoping to make this feature more reusable for other usecase in the future. for example it would be nice
> to be able to say this set of host has the CUSTOM_DPDK_NETWORKING trait by putting them in a host aggrage and then
> adding a forbindent trait to my non hugepage backed guests.
> > 
> > > there is also an option d. when you remove a trait form a host aggregate for each host in
> > > the aggregate check if that traits exists on another aggregate the host is a member of and remove
> > > it if not found on another aggregate.
> > 
> > Sorry I wasn't clear, (b) also does this ^ but with the condition that
> > also checks for the _AGGREGATE_ISOLATION_ infix.
> > 
> > > for c you still have to deal with the fact a host can be in multiple
> > 
> > host aggrates too by
> > > the way so jsut because a thread is namespace d and it is removed from
> > 
> > an aggrate does not
> > > mean its correcct to remove it from a host.
> > 
> > Right - in reality, there should be one algorithm, idempotent, to sync
> > host RP traits when anything happens to aggregates. It always goes out
> > and does the appropriate {set} math to decide which traits should exist
> > on which hosts and effects any necessary changes.
> > 
> > And yes, the performance will suck in a large deployment, because we
> > have to get all the compute RPs in all the aggregates (even the ones
> > with no trait metadata) to do that calculation. But aggregate operations
> > are fairly rare, aren't they?
> > 
> > Perhaps this is where we provide a nova-manage tool to do (b)'s sync
> > manually (which we'll surely have to do anyway as a "heal" or for
> > upgrades). So if you're not using the feature, you don't suffer the penalty.
> > 
> > > for example we talked about useing a hyperthreading trait in the cpu pinning spec which
> > > will not be managed by the compute driver. host aggages would be a convient way
> > > to be able to manage that trait if this was a generic feature.
> > 
> > Oh, okay, yeah, I don't accept this as a use case for this feature. It
> > will work, but we shouldn't recommend it precisely because it's
> > asymmetrical (you can't remove the trait by removing it from the
> > aggregate).
> 
> why not we do not expect the virt driver to report the hypertreading trait
> since we said it can be extrenally managed. even if we allowed the virt drvier to
> conditionally report it only when it frst creates a RP it is not allowed to readd
> if it is remvoed by someone else.
> 
> > There are other ways to add a random trait to all hosts in
> > an aggregate (for host in `get providers in aggregate`; do openstack
> > resource provider trait add ...; done).
> > 
> > But for the sake of discussion, what about:
> > 
> > (e) Fully manual. Aggregate operations never touch (add or remove)
> > traits on host RPs. You always have to do that manually. As noted above,
> > it's easy to do - and we could make it easier with a tiny wrapper that
> > takes an aggregate, a list of traits, and an --add/--remove command. So
> > initially, setting up aggregate isolation is a two-step process, and in
> > the future we can consider making new API/CLI affordance that combines
> > the steps.
ya e could work too.
melanie added a similar functionality to osc placment for managing the alloction ratios
of specific resource classes per aggregate a few months ago 
https://review.opendev.org/#/c/640898/

we could proably provide somthing similar for managing traits but determining what RP to
add the trait too would be a littel tricker. we would have to be able to filter to RP with either a
specific inventory or with a specific trait or in a speicic subtree.

you could have a --root or somthing to jsut say add or remove the tratit from the root RPs in an
aggregate. but yes you could certely automate this in a simile cli extention.
> > 
> > efried
> > .
> > 
> 
>