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[Openstack] [nova][cinder] Migrate instances between regions or between clusters?


On Tue, Sep 18, 2018 at 11:32:37AM +0200, Attila Fazekas wrote:
[format recovered; top-posting after an inline reply looks confusing]
> On Mon, Sep 17, 2018 at 11:43 PM, Jay Pipes <jaypipes at gmail.com> wrote:
> 
> > On 09/17/2018 09:39 AM, Peter Penchev wrote:
> >
> >> Hi,
> >>
> >> So here's a possibly stupid question - or rather, a series of such :)
> >> Let's say a company has two (or five, or a hundred) datacenters in
> >> geographically different locations and wants to deploy OpenStack in both.
> >> What would be a deployment scenario that would allow relatively easy
> >> migration (cold, not live) of instances from one datacenter to another?
> >>
> >> My understanding is that for servers located far away from one another
> >> regions would be a better metaphor than availability zones, if only
> >> because it would be faster for the various storage, compute, etc.
> >> services to communicate with each other for the common case of doing
> >> actions within the same datacenter.  Is this understanding wrong - is it
> >> considered all right for groups of servers located in far away places to
> >> be treated as different availability zones in the same cluster?
> >>
> >> If the groups of servers are put in different regions, though, this
> >> brings me to the real question: how can an instance be migrated across
> >> regions?  Note that the instance will almost certainly have some
> >> shared-storage volume attached, and assume (not quite the common case,
> >> but still) that the underlying shared storage technology can be taught
> >> about another storage cluster in another location and can transfer
> >> volumes and snapshots to remote clusters.  From what I've found, there
> >> are three basic ways:
> >>
> >> - do it pretty much by hand: create snapshots of the volumes used in
> >>    the underlying storage system, transfer them to the other storage
> >>    cluster, then tell the Cinder volume driver to manage them, and spawn
> >>    an instance with the newly-managed newly-transferred volumes
> >>
> >
> > Yes, this is a perfectly reasonable solution. In fact, when I was at AT&T,
> > this was basically how we allowed tenants to spin up instances in multiple
> > regions: snapshot the instance, it gets stored in the Swift storage for the
> > region, tenant starts the instance in a different region, and Nova pulls
> > the image from the Swift storage in the other region. It's slow the first
> > time it's launched in the new region, of course, since the bits need to be
> > pulled from the other region's Swift storage, but after that, local image
> > caching speeds things up quite a bit.
> >
> > This isn't migration, though. Namely, the tenant doesn't keep their
> > instance ID, their instance's IP addresses, or anything like that.

Right, sorry, I should have clarified that what we're interested in is
technically creating a new instance with the same disk contents, so
that's fine.  Thanks for confirming that there is not a simpler way that
I've missed, I guess :)

> > I've heard some users care about that stuff, unfortunately, which is why
> > we have shelve [offload]. There's absolutely no way to perform a
> > cross-region migration that keeps the instance ID and instance IP addresses.
> >
> > - use Cinder to backup the volumes from one region, then restore them to
> >>    the other; if this is combined with a storage-specific Cinder backup
> >>    driver that knows that "backing up" is "creating a snapshot" and
> >>    "restoring to the other region" is "transferring that snapshot to the
> >>    remote storage cluster", it seems to be the easiest way forward (once
> >>    the Cinder backup driver has been written)
> >>
> >
> > Still won't have the same instance ID and IP address, which is what
> > certain users tend to complain about needing with move operations.
> >
> > - use Nova's "server image create" command, transfer the resulting
> >>    Glance image somehow (possibly by downloading it from the Glance
> >>    storage in one region and simulateneously uploading it to the Glance
> >>    instance in the other), then spawn an instance off that image
> >>
> >
> > Still won't have the same instance ID and IP address :)
> >
> > Best,
> > -jay
> >
> > The "server image create" approach seems to be the simplest one,
> >> although it is a bit hard to imagine how it would work without
> >> transferring data unnecessarily (the online articles I've seen
> >> advocating it seem to imply that a Nova instance in a region cannot be
> >> spawned off a Glance image in another region, so there will need to be
> >> at least one set of "download the image and upload it to the other
> >> side", even if the volume-to-image and image-to-volume transfers are
> >> instantaneous, e.g. using glance-cinderclient).  However, when I tried
> >> it with a Nova instance backed by a StorPool volume (no ephemeral image
> >> at all), the Glance image was zero bytes in length and only its metadata
> >> contained some information about a volume snapshot created at that
> >> point, so this seems once again to go back to options 1 and 2 for the
> >> different ways to transfer a Cinder volume or snapshot to the other
> >> region.  Or have I missed something, is there a way to get the "server
> >> image create / image download / image create" route to handle volumes
> >> attached to the instance?
> >>
> >> So... have I missed something else, too, or are these the options for
> >> transferring a Nova instance between two distant locations?
> >>
> >> Thanks for reading this far, and thanks in advance for your help!
> >>
> >> Best regards,
> >> Peter
> 
> Create a volume transfer VM/machine in each region.
> attache the volume -> dd -> compress  -> internet   ->decompress -> new
> volume, attache(/boot with) to the volume to the final machine.
> In case you have frequent transfers you may keep up the machines for the
> next one..

Thanks for the advice, but this would involve transferring *a lot* more
data than if we leave it to the underlying storage :)  As I mentioned,
the underlying storage can be taught about remote clusters and can be told
to create a remote snapshot of a volume; this will be the base on which
we will write our Cinder backup driver.  So both my options 1 (do it "by
hand" with the underlying storage) and 2 (cinder volume backup/restore)
would be preferable.

> In case the storage is just on the compute node: snapshot ->glance download
> ->glance upload

Right, as I mentioned in my description of the third option, this does
not really work with attached volumes (thus your "just on the compute node")
and as I mentioned before listing the options, the instances will almost
certainly have attached volumes.

> Would be nice if cinder/glance could take the credentials for another
> openstack and move the volume/image to another cinder/glance.
> 
> If you want the same IP , specify the ip at instance boot time (port
> create),
> but you cannot be sure the same ip is always available or really route-able
> to different region.. unless... VPN like solution in place...
> 
> The uuid not expected to be changed by the users or admins (unsafe),
> but you can use other metadata for description/your uuid.

Best regards,
Peter

-- 
Peter Penchev  openstack-dev at storpool.com  https://storpool.com/