Hook error when MetalLB is not enabled

[gruyaume]

Describe the bug

We are getting a hook failed error whenever relating AMF to gNBSIM whenever the external LB is not set in the AMF.

Expected behavior

Charm should go to blocked status.

Logs

guillaume@thinkpad:~$ juju status
Model  Controller  Cloud/Region        Version  SLA          Timestamp
dev    localhost   microk8s/localhost  3.1.6    unsupported  16:08:24+02:00

App                       Version  Status   Scale  Charm                     Channel  Rev  Address         Exposed  Message
gnbsim                             waiting      1  sdcore-gnbsim             edge      35  10.152.183.153  no       waiting for units to settle down
mongodb-k8s                        active       1  mongodb-k8s               6/edge    37  10.152.183.84   no       Primary
sdcore-amf                         waiting      1  sdcore-amf                edge      43  10.152.183.132  no       installing agent
sdcore-ausf                        active       1  sdcore-ausf               edge      32  10.152.183.254  no       
sdcore-nrf                         active       1  sdcore-nrf                edge      51  10.152.183.253  no       
sdcore-nssf                        active       1  sdcore-nssf               edge      30  10.152.183.37   no       
sdcore-pcf                         active       1  sdcore-pcf                edge      24  10.152.183.158  no       
sdcore-router                      active       1  sdcore-router             edge      26  10.152.183.59   no       
sdcore-udm                         active       1  sdcore-udm                edge      28  10.152.183.46   no       
sdcore-udr                         active       1  sdcore-udr                edge      24  10.152.183.21   no       
self-signed-certificates           active       1  self-signed-certificates  edge      43  10.152.183.44   no       
webui                              active       1  sdcore-webui              edge      18  10.152.183.237  no       

Unit                         Workload  Agent  Address      Ports  Message
gnbsim/0*                    waiting   idle   10.1.19.166         Waiting for N2 information
mongodb-k8s/0*               active    idle   10.1.19.137         Primary
sdcore-amf/0*                error     idle   10.1.19.140         hook failed: "fiveg-n2-relation-joined"
sdcore-ausf/0*               active    idle   10.1.19.149         
sdcore-nrf/0*                active    idle   10.1.19.146         
sdcore-nssf/0*               active    idle   10.1.19.159         
sdcore-pcf/0*                active    idle   10.1.19.162         
sdcore-router/0*             active    idle   10.1.19.163         
sdcore-udm/0*                active    idle   10.1.19.152         
sdcore-udr/0*                active    idle   10.1.19.155         
self-signed-certificates/0*  active    idle   10.1.19.143         
webui/0*                     active    idle   10.1.19.142         

unit-sdcore-amf-0: 16:05:29 ERROR unit.sdcore-amf/0.juju-log fiveg-n2:19: Uncaught exception while in charm code:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/./src/charm.py", line 686, in <module>
    main(AMFOperatorCharm)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/venv/ops/main.py", line 436, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/venv/ops/main.py", line 144, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/venv/ops/framework.py", line 340, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/venv/ops/framework.py", line 842, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/venv/ops/framework.py", line 931, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/./src/charm.py", line 386, in _on_n2_relation_joined
    self._set_n2_information()
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/./src/charm.py", line 425, in _set_n2_information
    amf_ip_address=self._get_n2_amf_ip(),
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/./src/charm.py", line 399, in _get_n2_amf_ip
    return self._amf_external_service_ip()
  File "/var/lib/juju/agents/unit-sdcore-amf-0/charm/./src/charm.py", line 645, in _amf_external_service_ip
    return service.status.loadBalancer.ingress[0].ip  # type: ignore[attr-defined]
TypeError: 'NoneType' object is not subscriptable

Environment

• Juju version: 3.1.6
• Cloud Environment: MicroK8s
• Kubernetes version: v1.27.6