libvirt users - Apr 2016 - Re: Create multiple domains from single saved domain state (is UUID/name fixed?)

Hi,

I would like to save a running domain (ie. disk + memory) and be able to
restore it multiple times creating duplicates of the orignal domain all
starting from the same state.
Use case:
I'm building a task-processing system for use in a CI flow.
I want to run multiple VMs in parallel using the same image (always
starting from the same state).
And to avoid needlessly booting between each task, I would like to save
(and distribute) the domain state, so that I just restore from memory.

However, I can't seems to change the UUID or the name of a domain once it
is saved.
Nor do I seem able to rename a domain while it is running.

I can obviously duplicate both the disks and the file to which I saved the
domain state using "virsh save".
But I seem unable to rename before I restore.. Any ideas?

Could I do this with snapshots? I suspect not since I see
virDomainSnapshotRedefinePrep() calling
virDomainDefCheckABIStability which raises the error here:
https://fossies.org/dox/libvirt-1.3.3/domain__conf_8c_source.html#l17991

Out of curiosity does anyone know what horrors might befall me if I were to
remove the lines protecting against name and UUID changes? Then compile my
own libvirt...
The comment in the code says name can be changed, but I'm guessing I would
have to change the UUID too. Does anyone see how that would create issues?
I'm not sure how libvirt uses the UUID internally.

--
Regards Jonas Finnemann Jensen.

Hi Jonas,

I asked a similar question here last week. You could find it by searching
for this topic in the mailing list archives: "Clone VM with saved
state".
That being said I'd be very glad if you could update here when you find a
complete solution.

- Michael

On Mon, Apr 18, 2016 at 9:49 PM, Jonas Finnemann Jensen
<jonasfj@mozilla.com
> wrote:
> Hi,
>
> I would like to save a running domain (ie. disk + memory) and be able to
> restore it multiple times creating duplicates of the orignal domain all
> starting from the same state.
> Use case:
> I'm building a task-processing system for use in a CI flow.
> I want to run multiple VMs in parallel using the same image (always
> starting from the same state).
> And to avoid needlessly booting between each task, I would like to save
> (and distribute) the domain state, so that I just restore from memory.
>
> However, I can't seems to change the UUID or the name of a domain once
it
> is saved.
> Nor do I seem able to rename a domain while it is running.
>
> I can obviously duplicate both the disks and the file to which I saved the
> domain state using "virsh save".
> But I seem unable to rename before I restore.. Any ideas?
>
> Could I do this with snapshots? I suspect not since I see
> virDomainSnapshotRedefinePrep() calling
> virDomainDefCheckABIStability which raises the error here:
> https://fossies.org/dox/libvirt-1.3.3/domain__conf_8c_source.html#l17991
>
> Out of curiosity does anyone know what horrors might befall me if I were
> to remove the lines protecting against name and UUID changes? Then compile
> my own libvirt...
> The comment in the code says name can be changed, but I'm guessing I
would
> have to change the UUID too. Does anyone see how that would create issues?
> I'm not sure how libvirt uses the UUID internally.
>
> --
> Regards Jonas Finnemann Jensen.
>
> _______________________________________________
> libvirt-users mailing list
> libvirt-users@redhat.com
> https://www.redhat.com/mailman/listinfo/libvirt-users
>

On Mon, Apr 18, 2016 at 10:05:02PM +0300, Michael Ravits
wrote:
>Hi Jonas,
>
>I asked a similar question here last week. You could find it by searching
>for this topic in the mailing list archives: "Clone VM with saved
state".
>That being said I'd be very glad if you could update here when you find
a
>complete solution.
>
>- Michael
>
What I *think* Jones wants is to use virt-builder, it could cause some
problems if you started all of them.  What Michael wants is:

  virsh save running_domain saved-image-file.img
  virsh save-image-edit saved-image-file.img

Hope that helped,
Martin
>On Mon, Apr 18, 2016 at 9:49 PM, Jonas Finnemann Jensen
<jonasfj@mozilla.com
>> wrote:
>
>> Hi,
>>
>> I would like to save a running domain (ie. disk + memory) and be able
to
>> restore it multiple times creating duplicates of the orignal domain all
>> starting from the same state.
>> Use case:
>> I'm building a task-processing system for use in a CI flow.
>> I want to run multiple VMs in parallel using the same image (always
>> starting from the same state).
>> And to avoid needlessly booting between each task, I would like to save
>> (and distribute) the domain state, so that I just restore from memory.
>>
>> However, I can't seems to change the UUID or the name of a domain
once it
>> is saved.
>> Nor do I seem able to rename a domain while it is running.
>>
>> I can obviously duplicate both the disks and the file to which I saved
the
>> domain state using "virsh save".
>> But I seem unable to rename before I restore.. Any ideas?
>>
>> Could I do this with snapshots? I suspect not since I see
>> virDomainSnapshotRedefinePrep() calling
>> virDomainDefCheckABIStability which raises the error here:
>>
https://fossies.org/dox/libvirt-1.3.3/domain__conf_8c_source.html#l17991
>>
>> Out of curiosity does anyone know what horrors might befall me if I
were
>> to remove the lines protecting against name and UUID changes? Then
compile
>> my own libvirt...
>> The comment in the code says name can be changed, but I'm guessing
I would
>> have to change the UUID too. Does anyone see how that would create
issues?
>> I'm not sure how libvirt uses the UUID internally.
>>
>> --
>> Regards Jonas Finnemann Jensen.
>>
>> _______________________________________________
>> libvirt-users mailing list
>> libvirt-users@redhat.com
>> https://www.redhat.com/mailman/listinfo/libvirt-users
>>
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