Can't assign machines/units to (EC2, MAAS, etc.) availability zones in bundles

[George Kraft]

When deploying standalone, it's possible to assign units or machines to a specific availability zone on EC2:

juju add-machine zone=us-east-1c
juju deploy ubuntu --to zone=us-east-1c

When deploying a bundle, though, it seems there is no way to do this.

This would be helpful for custom deployments of canonical-kubernetes, where units integrate directly with AWS in order to make use of ELB and EBS functionality within Kubernetes. EBS volumes in particular are tied to specific availability zones, which makes the placement of kubernetes-worker units within availability zones important.