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

Russell Bryant rbryant at redhat.com
Wed Jan 8 16:44:17 UTC 2014

On 01/08/2014 09:53 AM, John Garbutt wrote:
> On 8 January 2014 10:02, David Xie <david.scriptfan at gmail.com> wrote:
>> In nova/compute/api.py#2289, function resize, there's a parameter named
>> flavor_id, if it is None, it is considered as cold migration. Thus, nova
>> should skip resize verifying. However, it doesn't.
>> Like Jay said, we should skip this step during cold migration, does it make
>> sense?
> Not sure.
>> On Wed, Jan 8, 2014 at 5:52 PM, Jay Lau <jay.lau.513 at gmail.com> 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?
> I think the idea was allow users/admins to check everything went OK,
> and only delete the original VM when the have confirmed the move went
> OK.
> I thought there was an auto_confirm setting. Maybe you want
> auto_confirm cold migrate, but not auto_confirm resize?

I suppose we could add an API parameter to auto-confirm these things.
That's probably a good compromise.

>>> 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.
> We just stop the VM them perform the migration.
> I don't think we need to require its stopped first.
> Am I missing something?

Don't think so ... I think we should leave it as is.

Russell Bryant

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