Mongo unit error state on teardown

[markbeierl]

Steps to reproduce

Destroy a model with multiple applications relationed to mongodb-k8s.

Expected behavior

Model tears down cleanly

Actual behavior

Mongo charm goes into error state. The following is observed in the juju debug-log:

Versions

Operating system: Ubuntu 22.04.3 LTS
Juju CLI: 3.1.7-genericlinux-amd64
Juju agent: 3.1.7
Charm revision: 5/edge 36
microk8s: MicroK8s v1.27.7 revision 6101

Log output

Juju debug log:
log.txt

unit-mongodb-k8s-0: 20:46:42 INFO unit.mongodb-k8s/0.juju-log database:15: Update relation user: relation-7 on free5gc
unit-mongodb-k8s-0: 20:46:42 INFO unit.mongodb-k8s/0.juju-log database:15: Updating relation data according to diff
unit-mongodb-k8s-0: 20:46:42 ERROR unit.mongodb-k8s/0.juju-log database:15: Uncaught exception while in charm code:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/./src/charm.py", line 1218, in <module>
    main(MongoDBCharm)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/main.py", line 441, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/main.py", line 149, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/framework.py", line 344, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/framework.py", line 833, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/framework.py", line 922, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/lib/charms/mongodb/v0/mongodb_provider.py", line 97, in _on_relation_event
    self.oversee_users(departed_relation_id, event)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/lib/charms/mongodb/v0/mongodb_provider.py", line 149, in oversee_users
    self._diff(event)
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/lib/charms/mongodb/v0/mongodb_provider.py", line 175, in _diff
    key: value for key, value in event.relation.data[event.app].items() if key != "data"
  File "/var/lib/juju/agents/unit-mongodb-k8s-0/charm/venv/ops/model.py", line 1361, in __getitem__
    raise KeyError(
KeyError: 'Cannot index relation data with "None". Are you trying to access remote app data during a relation-broken event? This is not allowed.'
unit-mongodb-k8s-0: 20:46:42 ERROR juju.worker.uniter.operation hook "database-relation-broken" (via hook dispatching script: dispatch) failed: exit status 1

[github-actions]

https://warthogs.atlassian.net/browse/DPE-3008

[ghislainbourgeois]

I hit the same bug when removing a mongo relation, with the exact same stack trace.

[dmitry-ratushnyy]

Thank you very much for reporting the issue, I will take a look into it within a week.

[dariofaccin]

This issue is still present in channel 6/beta revision 38.