On 1/20/2017 9:00 AM, Matt Riedemann wrote:
On 1/20/2017 4:53 AM, Eoghan Glynn wrote:
Do we also need to be concerned about the placement API "warm-up" time?
i.e. if a placement-less newton deployment is upgraded to placement-ful
ocata, then would there surely be a short period during which placement
is able to respond to the incoming queries from the scheduler, but only
with incomplete information since all the computes haven't yet triggered
their first reporting cycle?
In that case, it wouldn't necessarily lead to a NoValidHost failure on a
instance boot request, but rather a potentially faulty placement
decision,
being based on incomplete information. I mean "faulty" there in the sense
of not strictly following the configured scheduling strategy.
Is that a concern, or an acceptable short degradation of service?
Cheers,
Eoghan
That's discussed a bit in this older thread [1]. If placement is up and
running but there are no computes checking in yet, then it's going to be
a NoValidHost from the filter scheduler because it's not going to
fallback to the compute_nodes table.
The nova-status command was written as an upgrade readiness check for
this situation [2]. If there are compute nodes in the database (from
Newton) but no resource providers in the placement service, then that
upgrade check is going to fail.
If it's a fresh install and there are 0 resource providers in the
placement service and 0 compute nodes, then the upgrade check passes but
provides a reminder about needing to make sure you get the computes
configured and registered for placement as you bring them online.
[1]
http://lists.openstack.org/pipermail/openstack-dev/2016-December/109060.html
[2]
https://github.com/openstack/nova/blob/ae753d96281709397dcfe5dd4ff7d6db57f3683e/nova/cmd/status.py#L301
Also, before anyone mentions this:
"Well what if I've upgraded my controller services to Ocata, including
placement and nova-scheduler, but my computes are all still Newton?!"
The answer is Newton computes can be configured to register with the
placement service already, and we backported a fix from Dan Smith [1] to
make sure the Newton computes keep trying to connect to placement.
So this means you can still configure your Newton computes to talk to
the Ocata placement service, even before rolling out placement, and once
it's up the computes will check in and you shouldn't have NoValidHost
issues, or at least the window should be small.
[1] https://review.openstack.org/#/c/419217/
--
Thanks,
Matt Riedemann
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