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

Alex Xu xuhj at linux.vnet.ibm.com
Wed Jan 22 05:02:09 UTC 2014


On 2014?01?08? 23:12, Jay Lau wrote:
> 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.

I think cold migrate an ACTIVE VM is ok. The different of cold migration 
and live migration is there isn't down time for vm with live migration.  
Cold migration is make the vm
down first, then migrate it.

>
> What do you think?
>
> Thanks,
>
> Jay
>
>
>
> 2014/1/8 Russell Bryant <rbryant at redhat.com <mailto: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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