Comment 65 for bug 1603473

The bundle described in https://bugs.launchpad.net/juju/+bug/1603473/comments/61 doesn't have any "bindings" sections, which means you are not informing Juju of which space you want the charm to use, and thus we end up guessing.

Things like:
  ceph-radosgw:
    annotations:
      gui-x: '1000'
      gui-y: '250'
    charm: cs:trusty/ceph-radosgw-19
    num_units: 1
    options:
      source: cloud:trusty-liberty
      use-embedded-webserver: true
    to:
    - lxc:0

Could be updated to look like:
  ceph-radosgw:
    annotations:
      gui-x: '1000'
      gui-y: '250'
    charm: cs:trusty/ceph-radosgw-19
    num_units: 1
    options:
      source: cloud:trusty-liberty
      use-embedded-webserver: true
    to:
    - lxc:0
    bindings:
      "": maas-management

The "" binding is a "default for all otherwise unnamed endpoints". If you want one part of an application to use a different subnet, then you can list it explicitly. Eg:
  ceph-radosgw:
    annotations:
      gui-x: '1000'
      gui-y: '250'
    charm: cs:trusty/ceph-radosgw-19
    num_units: 1
    options:
      source: cloud:trusty-liberty
      use-embedded-webserver: true
    to:
    - lxc:0
    bindings:
      "": maas-management
      public: maas-external
      admin: maas-management
# not necessary as it is covered in "", but maybe explicit is good etc