Destroying deployed mongodb service fails with 'replica-set-relation-broken'

[Mario Splivalo]

When completely removing deployed mongodb service, the unit which is currently 'primary' will not get removed - it will remain stuck in this state:

agent-state-info: 'hook failed: "replica-set-relation-broken"'

This is the excerpt from the log file:

2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 Traceback (most recent call last):
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 File "/var/lib/juju/agents/unit-m7-0/charm/hooks/replica-set-relation-broken", line 1618, in <module>
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 hooks.execute(sys.argv)
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 File "/var/lib/juju/agents/unit-m7-0/charm/hooks/charmhelpers/core/hookenv.py", line 528, in execute
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 self._hooks[hook_name]()
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 File "/var/lib/juju/agents/unit-m7-0/charm/hooks/replica-set-relation-broken", line 1238, in replica_set_relation_broken
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 master_node = r['primary']
2015-03-24 19:27:18 INFO unit.m7/0.replica-set-relation-broken logger.go:40 KeyError: 'primary'

The workaround is to manually resolve failed unit with 'juju resolved'. After that juju will remove the unit, and completely destroy the service.