[openstack-dev] [nova] should we have a stale data indication in "nova list/show"?

Joe Gordon joe.gordon0 at gmail.com
Tue Jun 24 21:38:51 UTC 2014

On Jun 24, 2014 2:31 PM, "Russell Bryant" <rbryant at redhat.com> wrote:
> On 06/24/2014 04:42 PM, Joe Gordon wrote:
> >
> > On Jun 18, 2014 3:03 PM, "Chris Friesen" <chris.friesen at windriver.com
> > <mailto:chris.friesen at windriver.com>> wrote:
> >>
> >> The output of "nova list" and "nova show" reflects the current status
> > in the database, not the actual state on the compute node.
> >>
> >> If the instances in question are on a compute node that is currently
> > "down", then the information is stale and possibly incorrect.  Would
> > there be any benefit in adding some sort of indication of this in the
> > "nova list" output?  Or do we expect the end-user to check "nova
> > service-list" (or other health-monitoring mechanisms) to see if the
> > compute node is "up" before relying on the output of "nova list"?
> >
> > Great question.  In general I don't think a regular user should never
> > need to run any health monitoring command. I think the larger question
> > here is what how do we handle instances associated with a nova-compute
> > that is currently being reported as down.  If nova-compute is down we
> > have no way of knowing the actual state of the instances. Perhaps we
> > should move those instances to an error state and let the user respond
> > accordingly (delete instance etc.). And if the Nova-compute service
> > returns we correct the state.
> There be dragons here.  Just because Nova doesn't see the node reporting
> in, doesn't mean the VMs aren't actually still running.  I think this
> needs to be left to logic outside of Nova.
> For example, if your deployment monitoring really does think the host is
> down, you want to make sure it's *completely* dead before taking further
> action such as evacuating the host.  You certainly don't want to risk
> having the VM running on two different hosts.  This is just a business I
> don't think Nova should be getting in to.

I agree nova shouldn't take any actions. But I don't think leaving an
instance as 'active' is right either.  I was thinking move instance to
error state (maybe an unknown state would be more accurate) and let the
user deal with it, versus just letting the user deal with everything. Since
nova knows something *may* be wrong shouldn't we convey that to the user
(I'm not 100% sure we should myself).

> --
> Russell Bryant
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