Add to OS::Heat::AutoScalingGroup a property that lists resource IDs (you might informally think of these as resource names, but see http://docs.openstack.org/developer/heat/template_guide/hot_spec.html#resources-section) that no member may have. This is expected to be useful in the context of an update operation, as a principled way to get the resource group to remove undesirable existing members (whose IDs appear in this new property) and replace them appropriately. As a bit of convenient hygiene on behalf of users: the scaling group, upon completion of such an update (at which point no member has any excluded ID), forks an asynchronous invocation of the stack-update-by-deltas operation to remove the now-moot entries from the list of excluded IDs; for the sake of correctness in a concurrent world, this delta will not set the list to empty but rather remove the entries now known to be moot. This will cause another invocation of the scaling group's handle_update method, which will (unless concurrent activity introduced something) determine that nothing needs to be done.
Unknown
