[openstack-dev] [nova] locked instances and snaphot

Day, Phil philip.day at hp.com
Wed Jun 18 11:15:32 UTC 2014

> -----Original Message-----
> From: Ahmed RAHAL [mailto:arahal at iweb.com]
> Sent: 18 June 2014 01:21
> To: openstack-dev at lists.openstack.org
> Subject: Re: [openstack-dev] [nova] locked instances and snaphot
> Hi there,
> Le 2014-06-16 15:28, melanie witt a écrit :
> > Hi all,
> >
> [...]
> >
> > During the patch review, a reviewer raised a concern about the purpose
> > of instance locking and whether prevention of snapshot while an
> > instance is locked is appropriate. From what we understand, instance
> > lock is meant to prevent unwanted modification of an instance. Is
> > snapshotting considered a logical modification of an instance? That
> > is, if an instance is locked to a user, they take a snapshot, create
> > another instance using that snapshot, and modify the instance, have
> > they essentially modified the original locked instance?
> >
> > I wanted to get input from the ML on whether it makes sense to
> > disallow snapshot an instance is locked.
> Beyond 'preventing accidental change to the instance', locking could be seen
> as 'preventing any operation' to the instance.
> If I, as a user, lock an instance, it certainly only prevents me from accidentally
> deleting the VM. As I can unlock whenever I need to, there seems to be no
> other use case (chmod-like).

It bocks any operation that would stop the instance from changing state:  Delete, stop, start, reboot, rebuild, resize, shelve, pause, resume, etc

In keeping with that I don't see why it should block a snapshot, and having to unlock it to take a snapshot doesn't feel good either. 

> If I, as an admin, lock an instance, I am preventing operations on a VM and
> am preventing an ordinary user from overriding the lock.

The driver for doing this as an admin is slightly different - its to stop the user from changing the state of an instance rather than a protection.   A couple of use cases:
	- if you want to migrate a VM and the user is running a continual sequence of say reboot commands at it putting an admin lock in place gives you a way to break into that cycle.
	- There are a few security cases where we need to take over control of an instance, and make sure it doesn't get deleted by the user

> This is a form of authority enforcing that maybe should prevent even
> snapshots to be taken off that VM. The thing is that enforcing this beyond
> the limits of nova is AFAIK not there, so cloning/snapshotting cinder volumes
> will still be feasible.
> Enforcing it only in nova as a kind of 'security feature' may become
> misleading.
> The more I think about it, the more I get to think that locking is just there to
> avoid mistakes, not voluntary misbehaviour.
> --
> Ahmed
> _______________________________________________
> OpenStack-dev mailing list
> OpenStack-dev at lists.openstack.org
> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev

More information about the OpenStack-dev mailing list