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Le 19/01/2017 16:27, Matt Riedemann a écrit :
> Sylvain and I were talking about how he's going to work placement
> microversion requests into his filter scheduler patch [1]. He needs to
> make requests to the placement API with microversion 1.4 [2] or later
> for resource provider filtering on specific resource classes like VCPU
> and MEMORY_MB.
> 
> The question was what happens if microversion 1.4 isn't available in the
> placement API, i.e. the nova-scheduler is running Ocata code now but the
> placement service is running Newton still.
> 
> Our rolling upgrades doc [3] says:
> 
> "It is safest to start nova-conductor first and nova-api last."
> 
> But since placement is bundled with n-api that would cause issues since
> n-sch now depends on the n-api code.
> 
> If you package the placement service separately from the nova-api
> service then this is probably not an issue. You can still roll out n-api
> last and restart it last (for control services), and just make sure that
> placement is upgraded before nova-scheduler (we need to be clear about
> that in [3]).
> 
> But do we have any other issues if they are not packaged separately? Is
> it possible to install the new code, but still only restart the
> placement service before nova-api? I believe it is, but want to ask this
> out loud.
> 
> I think we're probably OK here but I wanted to ask this out loud and
> make sure everyone is aware and can think about this as we're a week
> from feature freeze. We also need to look into devstack/grenade because
> I'm fairly certain that we upgrade n-sch *before* placement in a grenade
> run which will make any issues here very obvious in [1].
> 
> [1] https://review.openstack.org/#/c/417961/
> [2]
> http://docs.openstack.org/developer/nova/placement.html#filter-resource-providers-having-requested-resource-capacity
> 
> [3]
> http://docs.openstack.org/developer/nova/upgrade.html#rolling-upgrade-process
> 
> 

I thought out loud in the nova channel at the following possibility :
since we always ask to upgrade n-cpus *AFTER* upgrading our other
services, we could imagine to allow the nova-scheduler gently accept to
have a placement service be Newton *UNLESS* you have Ocata computes.

On other technical words, the scheduler getting a response from the
placement service is an hard requirement for Ocata. That said, if the
response code is a 400 with a message saying that the schema is
incorrect, it would be checking the max version of all the computes and
then :
 - either the max version is Newton and then call back the
ComputeNodeList.get_all() for getting the list of nodes
 - or, the max version is Ocata (at least one node is upgraded), and
then we would throw a NoValidHosts

That way, the upgrade path would be :
 1/ upgrade your conductor
 2/ upgrade all your other services but n-cpus (we could upgrade and
restart n-sch before n-api, that would still work, or the contrary would
be fine too)
 3/ rolling upgrade your n-cpus

I think we would keep then the existing upgrade path and we would still
have the placement service be mandatory for Ocata.

Thoughts ?
-Sylvain