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

Ahmed RAHAL arahal at iweb.com
Wed Jun 25 02:49:55 UTC 2014


Le 2014-06-24 20:12, Joe Gordon a écrit :
>     Finally, assuming the customer had access to this 'unknown' state
>     information, what would he be able to do with it ? Usually he has no
>     lever to 'evacuate' or 'recover' the VM. All he could do is spawn
>     another instance to replace the lost one. But only if the VM really
>     is currently unavailable, an information he must get from other sources.
> If I was a user, and my instance went to an 'UNKNOWN' state, I would
> check if its still operating, and if not delete it and start another
> instance.

If I was a user and polled nova list/show on a regular basis just in 
case the management pane indicates a failure, I should have no 
expectation whatsoever. If service availability is my concern, I should 
monitor the service, nothing else. From there, once the service has 
failed, I can imagine checking if VM management is telling me something. 
However, if my service is down and I have no longer access to the VM ... 
simple case: destroy and respawn.

My point is that we should not make the nova state an expected source of 
truth regarding service availability in the VM, as there is no way to 
tell such a thing. If my VM is being DDOSed, nova would still say 
everything is fine, while my service is really down. In that situation, 
console access would help me determine if the VM management is wrong by 
stating everything is ok or if there is another root cause.
Similarly, should nova show a state change if load in the VM is through 
the roof and the service is not responsive ? or if OOM is killing all my 
processes because of a memory shortage ?

As stated before, providing such a state information is misleading 
because there are cases where node unavailability is not service 
disruptive, thus it would indicate a false positive while the opposite 
(everything is ok) is not at all indicative of a healthy status of the 

Maybe am I overseeing a use case here where you absolutely need the user 
of the service to know a potential problem with his hosting platform.


Ahmed Rahal <arahal at iweb.com> / iWeb Technologies
Spécialiste de l'Architecture TI
/ IT Architecture Specialist

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