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

Daniel P. Berrange berrange at redhat.com
Mon Aug 19 09:27:41 UTC 2013

On Mon, Aug 19, 2013 at 01:28:25AM -0700, Tim Smith wrote:
> On Sun, Aug 18, 2013 at 1:28 PM, Robert Collins
> <robertc at robertcollins.net>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.
> >
> > I agree that *that* is a big deal : is there something we could do to
> > prevent that happening? E.g. annotating this whole thing as
> > experimental/not upstream supported or something?
> >
> My understanding is that the live-snapshot extensions are to be disabled by
> default (either on the driver side or the API side) and must be explicitly
> enabled via a nova configuration change. Thus, it is not interferant with
> mainline codepaths by default, and the user will not place themself into an
> "unmaintainable" position unless they or their OpenStack distro provider
> flips that particular switch.
> That would seem to me a sufficiently high bar for preventing the user from
> shooting themselves in the foot. As for any objections to the mere
> _existence_ of the live-snapshot capability, I propose that the market
> answer the question as to whether or not the feature has value.

NB live-snapshots are fine if used for rollback/forward of an individual
VMs. It is only use of live snapshots for the purpose of cloning VMs
that's the issue here. Whether the market wants live cloning or not is
irrelevant until a vendor will actually support it from a technology POV

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