ScienceCloud Image Update

[TheChymera]

So, it seems that one cannot delete images on ScienceCloud (and I believe Openstack in general) as long as instances are still running based on them. Excerpt from email conversation:

Hello,

I am getting this issue, where I cannot delete an image while any instances which were generated based on it are running.
This happens both with the online GUI and the glance API.
[...]
Can you help me out?

Best,
Christian

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Dear Christian,

I am not sure I fully understood your questions but nonetheless I will provide you with some background on how the system works:
when you start an instance from an image what happens under the hood is that a COW clone is created and used as the instance root disk; as you can guess that in turn means that each instance needs to be able to reach the image from which it has started. Therefore by design you cannot delete an image if it has instances running from it.
If I understand correctly you are regularly uploading fresh images to the cloud. Assuming you are lifecycling your VM as often you should need just two gentoo images at the same time, the old one and the updated one.

I don't think I like the idea with 2 images. What would you suggest, @Doeme ? Reverting to the old, date-named format would be an option of last resort, I'd say.

[Doeme]

We don't need 2 but #of_instances+1.
I'd modify the process of creating an instance to include copying the image.
Otherwise just create a new image every time it is generated and try to garbage-collect the other ones