Should glance re-download an updated image from remote storage?

Asked by Major Hayden on 2012-04-27

We have some situations where we need to update an image in our remote storage repository which glance pulls images from. When we do that, we adjust the size and checksum in the glance registry to match the updated image. Glance will pull the image from cache, notice that the size doesn't match, and fail.

Would it be worthwhile to have glance re-download the image from the remote storage repository in this type of situation? Or, is there a better way to update images in a remote repository with glance?

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Major Hayden
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Eoghan Glynn (eglynn) said : #1

A point of information - we discussed image content mutability at the recent summit (in the context of restartable image downloads), and the conclusion was that image data (as opposed to metadata) are intended to be strictly immutable.

So what you're doing is not intended to be supported AFAIK.

That's not to say we couldn't make the cache more tolerant as you suggest.

Major Hayden (rackerhacker) said : #2

Thanks, Eoghan. That makes sense.