Die/warn of constraints which exceed available resources

On an Openstack provider, I did a deploy with "--constraints mem=32G", but in our environment, the available flavors only had a maximum of 16GB. The unit created was instead created with a 1GB memory flavor, without any sort of warning or notification.

Constraints should be a minimum bound (constrained to be the minimum above the requested constraints). Not being able to satisfy the minimum constraint should produce an error, or at the very least a warning plus selecting the maximum flavor closest to being able to satisfy the constraints.