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

melanie witt melwitt at outlook.com
Thu Jun 19 19:06:36 UTC 2014

On Jun 17, 2014, at 13:34, Andrew Laski <andrew.laski at rackspace.com> wrote:

> It appears that locking was added in 2010 (8aea573bd2e44e152fb4ef1627640bab1818dede), at which time commit messages weren't nearly as clear and helpful as they now are so there's not much insight from that.  But the lock checking methods added at that time have a docstring that includes "decorator used for preventing action against locked instances".  So the original intent seems to be that API actions would not be allowed against locked instances.  From that point of view snapshotting should be disallowed.

That's what I was going on initially too. I was ignorant about what locking instances is really for and didn't find documentation about it other than some anecdotal things in ML archive.

> Having said that, the main reason that I've heard for locks being used is to prevent accidental deletes.  And I've heard requests for locks that only prevent deletes.  So in my experience users want more granular locks, not more inclusive locking.  So I wouldn't consider it a bug that snapshots are allowed while an instance is locked.

That's interesting and good to know.

> But getting back to the original issue, I'm not sure locking snapshots is going to help.  The intent seems to be keeping users from gaining access to data that's within the instance.  But locks don't keep a user from seeing what's on the instance, or doing something like an LVM snapshot of the data from within the instance.

That's true and underscores why locking as a security measure doesn't make much sense. There are too many ways to get around it that you end up with a quite incomplete lockdown.

I think we have consensus that instance locking to protect content isn't an appropriate use of the feature and anyway isn't a complete solution to that problem. Instance locking prevents accidental changes/deletion of an instance by way of the api. And in Michael's example scenario of having to unlock (and risk accidental change/delete) in order to take a snapshot of an important instance, disabling snapshot of a locked instance would actively disrupt the expected use case of instance locking.

Thanks all for the discussion -- I learned a lot about this feature and I'll be updating the lp bug (not a bug) and review.

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