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

Matt Van Winkle mvanwink at rackspace.com
Fri Jun 12 13:27:16 UTC 2015

On 6/12/15 7:46 AM, "Andrew Laski" <andrew at lascii.com> wrote:

>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
>>> 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
>>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.

Completely agree with all your points, Andrew.  As someone who's starting
to live migrate more and more tenants, this is exactly the approach that
would be useful for me.


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