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

Russell Bryant rbryant at redhat.com
Tue Jun 24 21:31:16 UTC 2014

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.

Russell Bryant

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