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

Zhenyu Zheng zhengzhenyulixi at gmail.com
Mon Jul 27 01:39:47 UTC 2015

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
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?


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