Comment 9 for bug 1689683

I think we also need to figure out the same problem for Cinder AZs and multi storage backend scenarios.

https://github.com/juju/juju/blob/d7ab142/provider/openstack/provider.go#L1275-L1279

https://github.com/openstack/cinder/blob/master/releasenotes/notes/per-backend-az-28727aca360a1cc8.yaml

" Availability zones may now be configured per backend in a multi-backend
    configuration. Individual backend sections can now set the configuration
    option ``backend_availability_zone``. If set, this value will override
    the [DEFAULT] ``storage_availability_zone`` setting.
"

In my view, in a certain way we have a domain-specific language (DSL) per cloud to describe compute, storage and networking for machine allocation.

Juju implements availability zones (without specifying which ones exactly) and constraints, however, there are currently no good constraints/abstractions for multi-AZ, multi provider network, multi storage backend scenarios.

https://jujucharms.com/docs/2.2/charms-storage#openstack/cinder-(cinder)
"The OpenStack/Cinder provider does not currently have any specific configuration options."

For the networking side there is only one external network to allocate FIPs from, however, one might have multiple provider networks in general which is not modeled.

I think this deserves a separate wishlist type of issue.