Comment 5 for bug 1523506

So, Hans is right but the model is maybe a bit confusing. Let me explain :

The default AZ (eg. "nova") defined by the default_availability_zone Opt is only for allowing the AZ REST resource to show all the hosts behind a single AZ if not set. That doesn't imply that the host is attached to an aggregate explicitely defined as an AZ for partitioning.