The overcloud images are effectively coupled with a given version of tripleo-heat-templates. There will be images which are known *not* to work with a given version of tht but we should allow unknown images.

For example, the overcloud 7.1 images are known not to work with a 7.2 undercloud, but the deployment only fails very late in the stack.

I would like to suggest a blacklist of image checksums which lives in tripleo-heat-templates. tripleoclient can validate that the current glance overcloud-full image checksum doesn't match anything in the blacklist before starting a stack-create operation.

For stack-updates there would ideally need to be detection that a scale-up is happening, so that scale-up would fail early on a blacklisted image, but only a warning would be shown if there is no new nodes being created.