[Openstack-operators] [openstack-dev] [nova] about rebuild instance booted from volume

Tomáš Vondra vondra at homeatcloud.cz
Wed Mar 14 15:43:37 UTC 2018

I say delete! Delete them all!
Really, it's called delete_on_termination and should be ignored on Rebuild.
We have a VPS service implemented on top of OpenStack and do throw the old contents away on Rebuild. When the user has the Backup service paid, they can restore a snapshot. Backup is implemented as volume snapshot, then clone volume, then upload to image (glance is on a different disk array).

I also sometimes multi-attach a volume manually to a service node and just dd an image onto it. If it was to be implemented this way, then there would be no deleting a volume with delete_on_termination, just overwriting. But the effect is the same.

IMHO you can have snapshots of volumes that have been deleted. Just some backends like our 3PAR don't allow it, but it's not disallowed in the API contract.
Tomas from Homeatcloud

-----Original Message-----
From: Saverio Proto [mailto:zioproto at gmail.com] 
Sent: Wednesday, March 14, 2018 3:19 PM
To: Tim Bell; Matt Riedemann
Cc: OpenStack Development Mailing List (not for usage questions); openstack-operators at lists.openstack.org
Subject: Re: [Openstack-operators] [openstack-dev] [nova] about rebuild instance booted from volume

My idea is that if delete_on_termination flag is set to False the Volume should never be deleted by Nova.

my 2 cents


2018-03-14 15:10 GMT+01:00 Tim Bell <Tim.Bell at cern.ch>:
> Matt,
> To add another scenario and make things even more difficult (sorry (), if the original volume has snapshots, I don't think you can delete it.
> Tim
> -----Original Message-----
> From: Matt Riedemann <mriedemos at gmail.com>
> Reply-To: "OpenStack Development Mailing List (not for usage 
> questions)" <openstack-dev at lists.openstack.org>
> Date: Wednesday, 14 March 2018 at 14:55
> To: "openstack-dev at lists.openstack.org" 
> <openstack-dev at lists.openstack.org>, openstack-operators 
> <openstack-operators at lists.openstack.org>
> Subject: Re: [openstack-dev] [nova] about rebuild instance booted from 
> volume
>     On 3/14/2018 3:42 AM, 李杰 wrote:
>     >
>     >              This is the spec about  rebuild a instance booted from
>     > volume.In the spec,there is a
>     >        question about if we should delete the old root_volume.Anyone who
>     > is interested in
>     >        booted from volume can help to review this. Any suggestion is
>     > welcome.Thank you!
>     >        The link is here.
>     >        Re:the rebuild spec:https://review.openstack.org/#/c/532407/
>     Copying the operators list and giving some more context.
>     This spec is proposing to add support for rebuild with a new image for
>     volume-backed servers, which today is just a 400 failure in the API
>     since the compute doesn't support that scenario.
>     With the proposed solution, the backing root volume would be deleted and
>     a new volume would be created from the new image, similar to how boot
>     from volume works.
>     The question raised in the spec is whether or not nova should delete the
>     root volume even if its delete_on_termination flag is set to False. The
>     semantics get a bit weird here since that flag was not meant for this
>     scenario, it's meant to be used when deleting the server to which the
>     volume is attached. Rebuilding a server is not deleting it, but we would
>     need to replace the root volume, so what do we do with the volume we're
>     replacing?
>     Do we say that delete_on_termination only applies to deleting a server
>     and not rebuild and therefore nova can delete the root volume during a
>     rebuild?
>     If we don't delete the volume during rebuild, we could end up leaving a
>     lot of volumes lying around that the user then has to clean up,
>     otherwise they'll eventually go over quota.
>     We need user (and operator) feedback on this issue and what they would
>     expect to happen.
>     --
>     Thanks,
>     Matt
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