_external_url is bork

[PietroPasotti]

Bug Description

tempo coordinator errors out on relation to prometheus if s3 isn't integrated, because of an issue on how the external url is calculated.

To Reproduce

juju deploy cos-lite --channel edge
juju deploy tempo-coordinator-k8s --channel edge tempo
juju relate tempo prometheus

Environment

microk8s on top of openstack on top of multipass

(good luck)

Relevant log output

unit-tempo-0: 12:48:47 WARNING unit.tempo/0.juju-log metrics-endpoint:38: 'source_url' should start with a scheme, such as 'http://'. Assuming 'http:/
/' since none is present.                                                                                                                             
unit-tempo-0: 12:48:47 ERROR unit.tempo/0.juju-log metrics-endpoint:38: Uncaught exception while in charm code:                                       
Traceback (most recent call last):                                                                                                                    
  File "/var/lib/juju/agents/unit-tempo-0/charm/./src/charm.py", line 390, in <module>                                                                
    main(TempoCoordinatorCharm)                                                                                                                       
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/main.py", line 551, in main                                                                  
    manager.run()                                                                                                                                     
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/main.py", line 530, in run                                                                   
    self._emit()                                                                                                                                      
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/main.py", line 519, in _emit                                                                 
    _emit_charm_event(self.charm, self.dispatcher.event_name)                                                                                         
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/main.py", line 147, in _emit_charm_event                                                     
    event_to_emit.emit(*args, **kwargs)                                                                                                               
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/framework.py", line 348, in emit                                                             
    framework._emit(event)                                                                                                                            
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/framework.py", line 860, in _emit                                                            
    self._reemit(event_path)                                                                                                                          
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/framework.py", line 950, in _reemit                                                          
    custom_handler(event)                                                                                                                             
  File "/var/lib/juju/agents/unit-tempo-0/charm/lib/charms/prometheus_k8s/v0/prometheus_scrape.py", line 1527, in set_scrape_job_spec                 
    self._set_unit_ip()                                                                                                                               
  File "/var/lib/juju/agents/unit-tempo-0/charm/lib/charms/prometheus_k8s/v0/prometheus_scrape.py", line 1572, in _set_unit_ip                        
    relation.data[self._charm.unit]["prometheus_scrape_unit_address"] = unit_address                                                                  
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/model.py", line 1792, in __setitem__                                                         
    self._validate_write(key, value)                                                                                                                  
  File "/var/lib/juju/agents/unit-tempo-0/charm/venv/ops/model.py", line 1760, in _validate_write                                                     
    raise RelationDataTypeError(f'relation data values must be strings, not {type(value)}')                                                           
ops.model.RelationDataTypeError: relation data values must be strings, not <class 'NoneType'>                                                         
unit-tempo-0: 12:48:47 ERROR juju.worker.uniter.operation hook "metrics-endpoint-relation-joined" (via hook dispatching script: dispatch) failed: exit
 status 1                                                                                                                                             
unit-tempo-0: 12:48:47 INFO juju.worker.uniter awaiting error resolution for "relation-joined" hook

Additional context

No response

[mmkay]

It's easier to see even without the whole setup-on-setup:

1. deploy cos-lite first, then deploy tempo-coordinator and tempo-worker
2. jhack imatrix fill
3. no profit

It works if you deploy coordinator and worker first and relate them, then add cos-lite and jhack imatrix fill.

It might be an issue with the shared coordinator-worker object.

[PietroPasotti]

yes, the underlying issue is that tempo will not set up ingress until s3 is related and configured, and the _external_url property makes some incorrect assumptions about what TraefikRouteRequirer.is_ready means.

This should fix it:

    @property
    def _external_url(self) -> str:
        """Return the external url."""
        # traefik-route's is_ready() doesn't mean that there is data in the databags, hence the explicit checks.
        if self.ingress.is_ready() and self.ingress.scheme and self.ingress.external_host:
            ingress_url = f"{self.ingress.scheme}://{self.ingress.external_host}"