[openstack-dev] [nova] live-snapshot/cloning of virtual machines

Daniel P. Berrange berrange at redhat.com
Mon Aug 19 09:24:59 UTC 2013

On Mon, Aug 19, 2013 at 08:28:58AM +1200, Robert Collins wrote:
> On 17 August 2013 07:01, Russell Bryant <rbryant at redhat.com> wrote:
> >> Maybe we've grown up to the point where we have to be more careful and
> >> not introduce
> >> these kind of features and the maintenance cost of introducing
> >> experimental features is
> >> too great. If that is the community consensus, then I'm happy keep the
> >> live snapshot stuff
> >> in a branch on github for people to experiment with.
> >
> > My feeling after following this discussion is that it's probably best to
> > keep baking in another branch (github or whatever).  The biggest reason
> > is because of the last comment quoted from Daniel Berrange above.  I
> > feel that like that is a pretty big deal.
> So, reading between the lines here, I guess you're worried that we'd
> let code paths that violate what upstream will support leak into the
> main codepaths for libvirt - and thus we'd end up with a situation
> where we aren't supported by upstream for all regular operations.

Yes, if you perform a live clone of a VM, then you have effectively
tainted that VM for the rest of its lifetime. From the virt host
vendors' POV, any unexpected or problematic behaviour you get from
that VM thereafter will be outside scope of support. The onus would
be on the openstack sysadmin to demonstrate that the same problem
occurs without the use of live cloning.

Running a production cloud using a feature that your virt host
vendor considers unsupported would be somewhat reckless IMHO, unless
you think your sysadmins think they have the skills to solve all
possible problems in that area themselves, which is unlikely for most
cloud vendors.

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