[openstack-dev] [nova] Should we add instance action event to live migration?

Andrew Laski andrew at lascii.com
Fri Jun 12 12:46:45 UTC 2015

On 06/11/15 at 06:54pm, Ian Wells wrote:
>On 11 June 2015 at 12:37, Richard Raseley <richard at raseley.com> wrote:
>> Andrew Laski wrote:
>>> There are many reasons a deployer may want to live-migrate instances
>>> around: capacity planning, security patching, noisy neighbors, host
>>> maintenance, etc... and I just don't think the user needs to know or
>>> care that it has taken place.
>> They might care, insofar as live migrations will often cause performance
>> degradation from a users perspective.
>Seconded.  If your app manager is warned that you're going to be live
>migrating it can do something about the capacity drop.  I can imagine cases
>where a migrating VM would be brutally murdered [1] and replaced because
>it's not delivering sufficient performance.

To be clear I see instance-action reporting more as a log of what has 
previously happened to an instance, not a report of what's currently 
happening.  A live migration still has task_state changes to make it 
visible to a user.

My view is that in a cloud environment it shouldn't matter which host 
you're on, as long as it meets the scheduling constraints required, so a 
no-downtime movement between them is not an important event for a user.  
But that does ignore the performance drop-off that may be noticed by a 
user, so there are reasons to expose that information.  I'm just in 
favor of making it optional, not hiding it in general.

>[1] See "nova help brutally-murder"

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