[openstack-dev] [nova] live migration in Mitaka
paul.carlton2 at hpe.com
Wed Oct 7 09:26:05 UTC 2015
I'd be happy to take this on in Mitaka
On 07/10/15 10:14, Daniel P. Berrange wrote:
> On Tue, Oct 06, 2015 at 11:43:52AM -0600, Chris Friesen wrote:
>> On 10/06/2015 11:27 AM, Paul Carlton wrote:
>>> On 06/10/15 17:30, Chris Friesen wrote:
>>>> On 10/06/2015 08:11 AM, Daniel P. Berrange wrote:
>>>>> On Tue, Oct 06, 2015 at 02:54:21PM +0100, Paul Carlton wrote:
>>>>>> https://review.openstack.org/#/c/85048/ was raised to address the
>>>>>> migration of instances that are not running but people did not warm to
>>>>>> the idea of bringing a stopped/suspended instance to a paused state to
>>>>>> migrate it. Is there any work in progress to get libvirt enhanced to
>>>>>> perform the migration of non active virtual machines?
>>>>> Libvirt can "migrate" the configuration of an inactive VM, but does
>>>>> not plan todo anything related to storage migration. OpenStack could
>>>>> already solve this itself by using libvirt storage pool APIs to
>>>>> copy storage volumes across, but the storage pool worked in Nova
>>>>> is stalled
>>>> What is the libvirt API to migrate a paused/suspended VM? Currently nova uses
>>>> dom.managedSave(), so it doesn't know what file libvirt used to save the
>>>> state. Can libvirt migrate that file transparently?
>>>> I had thought we might switch to virDomainSave() and then use the cold
>>>> migration framework, but that requires passwordless ssh. If there's a way to
>>>> get libvirt to handle it internally via the storage pool API then that would
>>>> be better.
>>> So my reading of this is the issue could be addressed in Mitaka by
>>> is there any prospect of this being progressed?
>> Paul, that would avoid the need for cold migrations to use passwordless ssh
>> between nodes. However, I think there may be additional work to handle
>> migrating paused/suspended instances--still waiting for Daniel to address
>> that bit.
> Migrating paused VMs should "just work" - certainly at the libvirt/QEMU
> level there's no distinction between a paused & running VM wrt migration.
> I know that historically Nova has blocked migration if the VM is paused
> and I recall patches to remove that pointless restriction. I can't
> remember if they ever merged.
> For suspended instances, the scenario is really the same as with completely
> offline instances. The only extra step is that you need to migrate the saved
> image state file, as well as the disk images. This is trivial once you have
> done the code for migrating disk images offline, since its "just one more file"
> to care about. Officially apps aren't supposed to know where libvirt keeps
> the managed save files, but I think it is fine for Nova to peek behind the
> scenes to get them. Alternatively I'd be happy to see an API added to libvirt
> to allow the managed save files to be uploaded & downloaded via a libvirt
> virStreamPtr object, in the same way we provide APIs to upload & download
> disk volumes. This would avoid the need to know explicitly about the file
> location for the managed save image.
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