[openstack-dev] [cinder][nova] about re-image the volume

Sean McGinnis sean.mcginnis at gmx.com
Thu Mar 29 14:28:13 UTC 2018

>       This is the spec [0] about rebuild the volumed backed server.
> The question raised in the spec is about how to bandle the root volume.
> Finally,in Nova team,we think that the cleanest / best solution to this is to
> add a volume action API to cinder for re-imaging the volume.Once that is
> available in a new cinder v3 microversion, nova can use it. The reason I
> ...
>       So Nova team want Cinder to achieve the re-image api.But, I see a spec
> about volume revert by snapshot[1].It is so good for rebuild operation.In
> short,I have two ideas,one is change the volume revert by snapshot spec to
> re-image spec,not only it can let the volume revert by snapshot,but also can
> re-image the volume which the image's size is greater than 0;another idea is
> add a only re-image spec,it only can re-image the volume which the image's
> size is greater than 0.

I do not think changing the revert to snapshot implementation is appropriate
here. There may be some cases where this can get the desired result, but there
is no guarantee that there is a snapshot on the volume's base image state to
revert to. It also would not make sense to overload this functionality to
"revert to snapshot if you can, otherwise do all this other stuff instead."

This would need to be a new API (microversioned) to add a reimage call. I
wouldn't expect implementation to be too difficult as we already have that
functionality for new volumes. We would just need to figure out the most
appropriate way to take an already in-use volume, detach it, rewrite the image,
then reattach it.

Ideally, from my perspective, Nova would take care of the detach/attach portion
and Cinder would only need to take care of imaging the volume.


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