[openstack-dev] [OpenStack][Nova][cold migration] Why we need confirm resize after cold migration

Jay Lau jay.lau.513 at gmail.com
Wed Jan 8 15:12:38 UTC 2014


Thanks Russell, OK, will file a bug for first issue.

For second question, I want to show some of my comments here. I think that
we should disable cold migration for an ACTIVE VM as cold migrating will
first destroy the VM then re-create the VM when using KVM, I did not see a
use case why someone want to do such a case.

Even further, this might make end user confused, its really strange both
cold migration and live migration can migrate an ACTIVE VM. Cold migration
should only target STOPPED VM instance.

What do you think?

Thanks,

Jay



2014/1/8 Russell Bryant <rbryant at redhat.com>

> On 01/08/2014 04:52 AM, Jay Lau wrote:
> > Greetings,
> >
> > I have a question related to cold migration.
> >
> > Now in OpenStack nova, we support live migration, cold migration and
> resize.
> >
> > For live migration, we do not need to confirm after live migration
> finished.
> >
> > For resize, we need to confirm, as we want to give end user an
> > opportunity to rollback.
> >
> > The problem is cold migration, because cold migration and resize share
> > same code path, so once I submit a cold migration request and after the
> > cold migration finished, the VM will goes to verify_resize state, and I
> > need to confirm resize. I felt a bit confused by this, why do I need to
> > verify resize for a cold migration operation? Why not reset the VM to
> > original state directly after cold migration?
>
> The confirm step definitely makes more sense for the resize case.  I'm
> not sure if there was a strong reason why it was also needed for cold
> migration.
>
> If nobody comes up with a good reason to keep it, I'm fine with removing
> it.  It can't be changed in the v2 API, though.  This would be a v3 only
> change.
>
> > Also, I think that probably we need split compute.api.resize() to two
> > apis: one is for resize and the other is for cold migrations.
> >
> > 1) The VM state can be either ACTIVE and STOPPED for a resize operation
> > 2) The VM state must be STOPPED for a cold migrate operation.
>
> I'm not sure why would require different states here, though.  ACTIVE
> and STOPPED are allowed now.
>
> --
> Russell Bryant
>
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