juju-deployer --diff doesn't support multiple relations between same service pair

[JuanJo Ciarlante]

Doing 'juju-deployer --diff some-openstack.yaml' fails with:
Traceback (most recent call last):
  File "/usr/bin/juju-deployer", line 9, in <module>
    load_entry_point('juju-deployer==0.4.3', 'console_scripts', 'juju-deployer')()
  File "/usr/lib/python2.7/dist-packages/deployer/cli.py", line 130, in main
    run()
  File "/usr/lib/python2.7/dist-packages/deployer/cli.py", line 223, in run
    diff.Diff(env, deployment, options).run()
  File "/usr/lib/python2.7/dist-packages/deployer/action/diff.py", line 152, in run
    diff = self.do_diff()
  File "/usr/lib/python2.7/dist-packages/deployer/action/diff.py", line 148, in do_diff
    self.load_env()
  File "/usr/lib/python2.7/dist-packages/deployer/action/diff.py", line 34, in load_env
    rels.update(self._load_rels(svc_name))
  File "/usr/lib/python2.7/dist-packages/deployer/action/diff.py", line 49, in _load_rels
    rr_name = self._get_rel_name(svc_name, r_svc)
  File "/usr/lib/python2.7/dist-packages/deployer/action/diff.py", line 62, in _get_rel_name
    raise ValueError("Ambigious relations for service")
ValueError: Ambigious relations for service

Note that juju-deployer properly deploys it, but diff.py logic,
is failing on this YAML excerpt:
  relations:
    - [ ceilometer, "keystone:identity-service" ]
    - [ ceilometer, "keystone:identity-notifications" ]

FYI above relations as per
https://wiki.ubuntu.com/ServerTeam/OpenStackCharms/ReleaseNotes1501#Ceilometer

[Kapil Thangavelu (hazmat)]

so.. idle thoughts.. ibest practice i think is going to be using ensemble (github.com/kapilt/ensemble) for diffs. i haven't gotten around to incorporating it into deployer. but the diff logic there is significantly simpler and more robust as it implements a full backend/mock impl of core.

[JuanJo Ciarlante (jjo)]

@hazmat: tnx for the feedback, until we have that approach
ready, I'd appreciate your review on linked MP (all tests
pass, verified also against some of our deploys), as it's
quite a critical part of our production workflow, to assess
configs in-sync with environment.

[Robert Bruce Park (robru)]

This just bit me today, fortunately my second relation between two services was vestigial and I was able to solve the problem by removing a relation. Quite strange though, because this definitely used to work back when I added the second relation, perhaps a year ago.

[Tom Haddon (mthaddon)]

JuanJo is not going to have time to work on this for the next few weeks, so if we want to progress before then we'll need to find someone else to pick this up.