Hi everyone,

I got excited to hear that this live snapshot has been taken into 
discussion in our community. Recently my clients in China came up with 
this live snapshot requirement as well, because they have already had 
their legacy environment and expect the original functions work fine when 
they transfer to use OpenStack. In my opinion, we need to think a little 
bit about these clients' needs, because it is also a potential market for 
OpenStack.

I registered a new blueprint for Nova 
https://blueprints.launchpad.net/nova/+spec/driver-specific-snapshot. It 
is named driver-specific before, but can be changed later.

The Nova API could be implemented via the extension, the following API may 
be added:
• CreateSnapshot: create a snapshot from the VM. The snapshot can be live 
snapshot or other hypervisor native way to create a snapshot.
• RestoreFromSnapshot: restore/revert the VM from a snapshot.
• DeleteSnapshot: delete a snapshot.
• ListSnapshot: list all the snapshots or list all the snapshots if a VM 
id is given.
• SpawnFromSnapshot: spawn a new VM from an existing snapshot, which is 
the live snapshot or the snapshot of other snapshot created in a 
hypervisor native way.
The features in this blueprint can be optional for any drivers. If a 
driver does not have a "native way" to do live snapshot or other kind of 
snapshots, it is fine to leave the API not implemented; if a driver can 
provide the "native feature" to do snapshot, it is an opportunity to 
reinforce Nova with this snapshot support. 

I sincerely need your comments and hope we can figure it out in a most 
favorable way. 
Thank you so much.

Best wishes,
Vincent Hou (侯胜博)

Staff Software Engineer, Open Standards and Open Source Team, Emerging 
Technology Institute, IBM China Software Development Lab

Tel: 86-10-82450778 Fax: 86-10-82453660
Notes ID: Sheng Bo Hou/China/IBM@IBMCN    E-mail: sb...@cn.ibm.com 
Address:3F Ring, Building 28 Zhongguancun Software Park, 8 Dongbeiwang 
West Road, Haidian District, Beijing, P.R.C.100193
地址:北京市海淀区东北旺西路8号中关村软件园28号楼环宇大厦3层 邮编:100193



Jay Pipes <jaypi...@gmail.com> 
2014/03/12 03:15
Please respond to
"OpenStack Development Mailing List \(not for usage questions\)" 
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Subject
Re: [openstack-dev] [nova] a question about instance snapshot






On Tue, 2014-03-11 at 06:35 +0000, Bohai (ricky) wrote:
> > -----Original Message-----
> > From: Jay Pipes [mailto:jaypi...@gmail.com]
> > Sent: Tuesday, March 11, 2014 3:20 AM
> > To: openstack-dev@lists.openstack.org
> > Subject: Re: [openstack-dev] [nova] a question about instance snapshot
> >
> > On Mon, 2014-03-10 at 12:13 -0400, Shawn Hartsock wrote:
> > > We have very strong interest in pursing this feature in the VMware
> > > driver as well. I would like to see the revert instance feature
> > > implemented at least.
> > >
> > > When I used to work in multi-discipline roles involving operations 
it
> > > would be common for us to snapshot a vm, run through an upgrade
> > > process, then revert if something did not upgrade smoothly. This
> > > ability alone can be exceedingly valuable in long-lived virtual
> > > machines.
> > >
> > > I also have some comments from parties interested in refactoring how
> > > the VMware drivers handle snapshots but I'm not certain how much 
that
> > > plays into this "live snapshot" discussion.
> >
> > I think the reason that there isn't much interest in doing this kind 
of thing is
> > because the worldview that VMs are pets is antithetical to the 
worldview that
> > VMs are cattle, and Nova tends to favor the latter (where DRS/DPM on
> > vSphere tends to favor the former).
> >
> > There's nothing about your scenario above of being able to "revert" an 
instance
> > to a particular state that isn't possible with today's Nova.
> > Snapshotting an instance, doing an upgrade of software on the 
instance, and
> > then restoring from the snapshot if something went wrong (reverting) 
is
> > already fully possible to do with the regular Nova snapshot and 
restore
> > operations. The only difference is that the "live-snapshot"
> > stuff would include saving the memory view of a VM in addition to its 
disk state.
> > And that, at least in my opinion, is only needed when you are treating 
VMs like
> > pets and not cattle.
> >
> 
> Hi Jay,
> 
> I read every words in your reply and respect what you said.
> 
> But i can't agree with you that memory snapshot is a feature for pat not 
for cattle.
> I think it's a feature whatever what do you look the instance as.
> 
> The world doesn't care about what we look the instance as, in fact, 
currently almost all the
> mainstream hypervisors have supported the memory snapshot.
> If it's just a dispensable feature and no users need it, I can't 
understand why
> the hypervisors provide it without exception.
> 
> In the document " OPENSTACK OPERATIONS GUIDE" section " Live snapshots" 
has the
> below words:
> " To ensure that important services have written their contents to disk 
(such as, databases),
> we recommend you read the documentation for those applications to 
determine what commands
> to issue to have them sync their contents to disk. If you are unsure how 
to do this,
>  the safest approach is to simply stop these running services normally.
> "
> This just pushes all the responsibility to guarantee the consistency of 
the instance to the end user.
> It's absolutely not convenient and I doubt whether it's appropriate.

Hi Ricky,

I guess we will just have to disagree about the relative usefulness of
this kind of thing for users of the cloud (and not users of traditional
managed hosting) :) Like I said, if it does not affect the performance
of other tenants' instances, I'm fine with adding the functionality in a
way that is generic (not hypervisor-specific).

Best,
-jay


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