jujuclient.EnvError: <Env Error - Details: { u'Error': u'watcher was stopped', u'RequestId': 9, u'Response': { }}

When deploying the CI Airline we are seeing this error:

2014-02-24 12:43:18 Waiting for units before adding relations
Traceback (most recent call last):
  File "/tmp/tmpMXiOxi/deployer/cli.py", line 224, in <module>
    main()
  File "/tmp/tmpMXiOxi/deployer/cli.py", line 119, in main
    run()
  File "/tmp/tmpMXiOxi/deployer/cli.py", line 216, in run
    importer.Importer(env, deployment, options).run()
  File "/tmp/tmpMXiOxi/deployer/action/importer.py", line 191, in run
    self.wait_for_units()
  File "/tmp/tmpMXiOxi/deployer/action/importer.py", line 166, in wait_for_units
    int(timeout), watch=self.options.watch, no_exit=ignore_error)
  File "/tmp/tmpMXiOxi/deployer/env/go.py", line 225, in wait_for_units
    self.client.wait_for_units(timeout, goal_state, callback=callback)
  File "/usr/lib/python2.7/dist-packages/jujuclient.py", line 406, in wait_for_units
    return WaitForUnits(watch, goal_state).run(callback)
  File "/usr/lib/python2.7/dist-packages/jujuclient.py", line 690, in run
    for change_set in self.watch:
  File "/usr/lib/python2.7/dist-packages/jujuclient.py", line 216, in next
    return super(TimeoutWatcher, self).next()
  File "/usr/lib/python2.7/dist-packages/jujuclient.py", line 178, in next
    'Id': self.watcher_id})
  File "/usr/lib/python2.7/dist-packages/jujuclient.py", line 145, in _rpc
    raise EnvError(result)
jujuclient.EnvError: <Env Error - Details:
 { u'Error': u'watcher was stopped', u'RequestId': 9, u'Response': { }}
 >
Problem deploying "ci-airline-staging": Command '['juju-deployer', '-v', '-c', '/tmp/tmpoUnBMa/deployer/relations.yaml', '-c', '/tmp/tmpoUnBMa/deploye$/production-only.yaml', '-c', '/tmp/tmpoUnBMa/deployer/ppa-assigner.yaml', '-c', '/tmp/tmpoUnBMa/deployer/image-builder.yaml', '-c', '/tmp/tmpoUnBMa/de
ployer/juju-gui.yaml', '-c', '/tmp/tmpoUnBMa/deployer/lander.yaml', '-c', '/tmp/tmpoUnBMa/deployer/ticket-system.yaml', '-c', '/tmp/tmpoUnBMa/deployer/
branch-source-builder.yaml', '-c', '/tmp/tmpoUnBMa/deployer/test-runner.yaml', 'ci-airline-staging']' returned non-zero exit status 1

machine-0: http://paste.ubuntu.com/6986643/

We have tried this on 1gb and 2gb canonistack instances. This has happened in lcy01 and lcy02.

07:36:34 rogpeppe | hazmat, cjohnston: it looks like it might be a problem with mongo - the port it's getting a timeout error from
                    | is mongod's port
07:37:18 rogpeppe | hmm, but that's somewhat odd
07:37:54 cjohnston | hazmat: 'status' meaning 'juju status' ?
07:38:40 rogpeppe | cjohnston: yes
07:38:54 cjohnston | juju status works
07:39:21 rogpeppe | cjohnston: ok, so it seems like this is only a transient error, which is something
07:40:00 cjohnston | http://paste.ubuntu.com/6986741/
07:40:22 rogpeppe | cjohnston: thanks. that all looks healthy.
07:40:42 rogpeppe | cjohnston: did you find out about the issue from a GUI error?
07:41:30 hazmat | rogpeppe, from a deployer error, he's been reproducing this consistently for a week
07:41:43 cjohnston | http://paste.ubuntu.com/6986666/

juju-core: 1.17.3-0ubuntu1

To reproduce:

bzr branch lp:ubuntu-ci-services-itself
cd ubuntu-ci-services-itself
juju bootstrap
sshuttle
./juju-deployer/deploy.py