[Nova] Suggestion needed for detach-boot-volume design

Zhenyu Zheng zhengzhenyulixi at gmail.com
Mon Jan 7 08:37:50 UTC 2019

Thanks alot for the replies, lets wait for some more comments, and I will
update the follow-up spec about this within two days.

On Sat, Jan 5, 2019 at 7:37 AM melanie witt <melwittt at gmail.com> wrote:

> On Fri, 4 Jan 2019 09:50:46 -0600, Matt Riedemann <mriedemos at gmail.com>
> wrote:
> > On 1/2/2019 2:57 AM, Zhenyu Zheng wrote:
> >> I've been working on detach-boot-volume[1] in Stein, we got the initial
> >> design merged and while implementing we have meet some new problems and
> >> now I'm amending the spec to cover these new problems[2].
> >
> > [2] is https://review.openstack.org/#/c/619161/
> >
> >>
> >> The thing I want to discuss for wider opinion is that in the initial
> >> design, we planned to support detach root volume for only STOPPED and
> >> SHELVED/SHELVE_OFFLOADED instances. But then we found out that we
> >> allowed to detach volumes for RESIZED/PAUSED/SOFT_DELETED instances as
> >> well. Should we allow detaching root volume for instances in these
> >> status too? Cases like RESIZE could be complicated for the revert resize
> >> action, and it also seems unnecesary.
> >
> > The full set of allowed states for attaching and detaching are here:
> >
> >
> https://github.com/openstack/nova/blob/8ef3d253a/nova/compute/api.py#L4187
> >
> >
> https://github.com/openstack/nova/blob/8ef3d253a/nova/compute/api.py#L4297
> >
> > Concerning those other states:
> >
> > RESIZED: There might be a case for attaching/detaching volumes based on
> > flavor during a resize, but I'm not sure about the root volume in that
> > case (that really sounds more like rebuild with a new image to me, which
> > is a different blueprint). I'm also not sure how much people know about
> > the ability to do this or what the behavior is on revert if you have
> > changed the volumes while the server is resized. If we consider that
> > when a user reverts a resize, they want to go back to the way things
> > were for the root disk image, then I would think we should not allow
> > changing out the root volume while resized.
> Yeah, if someone attaches/detaches a regular volume while the instance
> is in VERIFY_RESIZE state and then reverts the resize, I assume we
> probably don't attempt to change or restore anything with the volume
> attachments to put them back to how they were attached before the
> resize. But as you point out, the situation does seem different
> regarding a root volume. If a user changes that while in VERIFY_RESIZE
> and reverts the resize, and we leave the root volume alone, then they
> end up with a different root disk image than they had before the resize.
> Which seems weird.
> I agree it seems better not to allow this for now and come back to it
> later if people start asking for it.
> > PAUSED: First, I'm not sure how much anyone uses the pause API (or
> > suspend for that matter) although most of the virt drivers implement it.
> > At one point you could attach volumes to suspended servers as well, but
> > because libvirt didn't support it that was removed from the API (yay for
> > non-discoverable backend-specific API behavior changes):
> >
> > https://review.openstack.org/#/c/83505/
> >
> > Anyway, swapping the root volume on a paused instance seems dangerous to
> > me, so until someone really has a good use case for it, then I think we
> > should avoid that one as well.
> >
> > SOFT_DELETED: I really don't understand the use case for
> > attaching/detaching volumes to/from a (soft) deleted server. If the
> > server is deleted and only hanging around because it hasn't been
> > reclaimed yet, there are really no guarantees that this would work, so
> > again, I would just skip this one for the root volume changes. If the
> > user really wants to play with the volumes attached to a soft deleted
> > server, they should restore it first.
> >
> > So in summary, I think we should just not support any of those other
> > states for attach/detach root volumes and only focus on stopped or
> > shelved instances.
> Again, agree, I think we should just not allow the other states for the
> initial implementation and revisit later if it turns out people need these.
> -melanie
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-discuss/attachments/20190107/2c9e186e/attachment.html>

More information about the openstack-discuss mailing list