Why would you want to take a snapshot of an image in glance? I mean, the image will never change when you spawn an instance from it because another copy of it is created when an instance is created.

This being said there is no straight forward command to take a snapshot of an image that i know of. You could spawn an instance from it, make the necesary changes to it and then take a snapshot of the instance. This will upload it into glance like a normal image.

Or you could create a bootable volume from the image, spawn an instace, make changes, terminate instance and than upload the volume into glance as an image!

Hello,

If you are going to create new environment (same openstack version, different servers), if you wan't to move all running instances to new environment.

You can migrate the running instances if your environment was configured for live migration.

(OR) you can take the snapshot of running instances:

1. create snapshots of the running instances with "nova image-create"

2. publish your /var/lib/glance/images via http OR use glance image-download to copy the snapshots somewhere and publish that directory via http

3. import those snaps in the new environment by using "glance image-create --copy-from"

Regards,
RHK