[openstack-dev] [nova][cinder] Should we allow this kind of action?

Chris Friesen chris.friesen at windriver.com
Mon Jul 27 17:33:54 UTC 2015

On 07/26/2015 07:39 PM, Zhenyu Zheng wrote:
> Hi all,
> Recently, I've been asked to perform this kind of action using OpenStack:
> 1. Launch an volume-backended instance.
> 2. Take a snapshot of this instance using nova image-create, an image will be
> added in glance, the size is zero, and the BDM will be saved in it's metadata.
> 3. Create an volume using this image (with Cinder), This volume will be marked
> with bootable.
> 4. Launch an new volume-backended instance using this newly built volume.
> There will be errors performing this action:
> 1. Cinder will create an volume with zero size and the BDM saved in metadata is
> transformed from dict to string and it is not able to be used in nova for
> instance creation.
> 2. The BDM is provided by user with REST API, and it will be conflict with the
> BDM saved in metadata.
> Now, my question is:
> Should we allow this kind of action in Nova? Or should we only use the image
> directly for instance creation.
> If this kind of action is not allowed, should we add checks in Cinder to forbid
> volume creation with an zero-sized image?

If we're going to allow snapshotting a boot-from-volume instance, then I think 
we should make it a "proper" image that can be used for any purpose that a 
regular image can be used.


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