Scale up operation should not crash the charm

[gatici]

Hello,

If we scale up self-signed-certificates operator, charm crashes with error "ops.model.ModelError: ERROR permission denied".
Although scaling operation is not implemented yet (needs to be implemented), this charm shouldn't crash when we try to do so. Non-leader unit should simply do nothing.
This problem needs to be fixed.

gatici@gaticipc:~/.ssh$ juju status
Model  Controller          Cloud/Region        Version  SLA          Timestamp
core   microk8s-localhost  microk8s/localhost  3.1.5    unsupported  01:25:01+03:00

SAAS        Status  Store               URL
loki        active  microk8s-localhost  admin/cos.loki
prometheus  active  microk8s-localhost  admin/cos.prometheus

App                       Version  Status   Scale  Charm                     Channel        Rev  Address         Exposed  Message
amf                                active       1  sdcore-amf                edge            21  10.152.183.39   no       
ausf                               active       1  sdcore-ausf               edge            14  10.152.183.202  no       
gnbsim                             active       1  sdcore-gnbsim             edge            17  10.152.183.159  no       
grafana-agent-k8s         0.32.1   active       1  grafana-agent-k8s         latest/stable   38  10.152.183.253  no       
mongodb-k8s                        active       1  mongodb-k8s               5/edge          35  10.152.183.250  no       
nrf                                active       1  sdcore-nrf                edge            31  10.152.183.201  no       
nssf                               active       1  sdcore-nssf               edge            16  10.152.183.19   no       
pcf                                active       1  sdcore-pcf                edge             7  10.152.183.119  no       
router                             active       1  sdcore-router             edge            11  10.152.183.207  no       
self-signed-certificates           waiting      3  self-signed-certificates  edge            17  10.152.183.40   no       installing agent
smf                                active       1  sdcore-smf                edge            17  10.152.183.22   no       
udm                                active       1  sdcore-udm                edge            13  10.152.183.158  no       
udr                                active       1  sdcore-udr                edge            15  10.152.183.71   no       
upf                                active       1  sdcore-upf                                 0  10.152.183.109  no       
webui                              active       1  sdcore-webui              edge             8  10.152.183.197  no       

Unit                         Workload  Agent  Address      Ports  Message
amf/0*                       active    idle   10.1.146.13         
ausf/0*                      active    idle   10.1.146.62         
gnbsim/0*                    active    idle   10.1.146.10         
grafana-agent-k8s/0*         active    idle   10.1.146.54         
mongodb-k8s/0*               active    idle   10.1.146.61         
nrf/0*                       active    idle   10.1.146.45         
nssf/0*                      active    idle   10.1.146.26         
pcf/0*                       active    idle   10.1.146.42         
router/0*                    active    idle   10.1.146.5          
self-signed-certificates/0*  active    idle   10.1.146.12         
self-signed-certificates/1   error     idle   10.1.146.57         hook failed: "certificates-relation-changed"
self-signed-certificates/2   error     idle   10.1.146.32         hook failed: "certificates-relation-changed"
smf/0*                       active    idle   10.1.146.46         
udm/0*                       active    idle   10.1.146.19         
udr/0*                       active    idle   10.1.146.38         
upf/0*                       active    idle   10.1.146.2          
webui/0*                     active    idle   10.1.146.3  

Juju debug log output:

unit-self-signed-certificates-1: 01:21:06 INFO juju.worker.uniter.operation ran "certificates-relation-created" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:06 INFO juju.worker.uniter.operation ran "certificates-relation-created" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-0: 01:21:07 INFO unit.self-signed-certificates/0.juju-log certificates:6: Generated certificate for relation 6
unit-self-signed-certificates-1: 01:21:07 INFO juju.worker.uniter.operation ran "leader-settings-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-0: 01:21:07 INFO juju.worker.uniter.operation ran "certificates-relation-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:07 INFO juju.worker.uniter.operation ran "leader-settings-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:08 INFO juju.worker.uniter.operation ran "config-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:08 INFO juju.worker.uniter found queued "start" hook
unit-self-signed-certificates-0: 01:21:08 INFO juju.worker.uniter.operation ran "secret-remove" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:08 INFO juju.worker.uniter.operation ran "config-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:08 INFO juju.worker.uniter found queued "start" hook
unit-self-signed-certificates-1: 01:21:08 INFO unit.self-signed-certificates/1.juju-log Running legacy hooks/start.
unit-self-signed-certificates-2: 01:21:08 INFO unit.self-signed-certificates/2.juju-log Running legacy hooks/start.
unit-ausf-0: 01:21:08 INFO juju.worker.uniter.operation ran "certificates-relation-changed" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:08 INFO juju.worker.uniter.operation ran "start" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:09 INFO juju.worker.uniter.operation ran "start" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:09 INFO juju.worker.uniter.operation ran "certificates-relation-joined" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:09 INFO juju.worker.uniter.operation ran "certificates-relation-joined" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:10 INFO juju.worker.uniter.operation ran "certificates-relation-joined" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:10 INFO juju.worker.uniter.operation ran "certificates-relation-joined" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-1: 01:21:10 INFO juju.worker.uniter.operation ran "certificates-relation-joined" hook (via hook dispatching script: dispatch)
unit-self-signed-certificates-2: 01:21:10 ERROR unit.self-signed-certificates/2.juju-log certificates:17: Uncaught exception while in charm code:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 2723, in _run
    result = subprocess.run(args, **kwargs)  # type: ignore
  File "/usr/lib/python3.10/subprocess.py", line 526, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '('/var/lib/juju/tools/unit-self-signed-certificates-2/relation-get', '-r', '17', '-', 'self-signed-certificates', '--app', '--format=json')' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/./src/charm.py", line 221, in <module>
    main(SelfSignedCertificatesCharm)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/main.py", line 441, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/main.py", line 149, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/framework.py", line 344, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/framework.py", line 841, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/framework.py", line 930, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/lib/charms/tls_certificates_interface/v2/tls_certificates.py", line 1106, in _on_relation_changed
    provider_relation_data = _load_relation_data(event.relation.data[self.charm.app])
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/lib/charms/tls_certificates_interface/v2/tls_certificates.py", line 604, in _load_relation_data
    for key in raw_relation_data:
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 679, in __iter__
    return iter(self._data)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 666, in _data
    data = self._lazy_data = self._load()
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 1397, in _load
    return self._backend.relation_get(self.relation.id, self._entity.name, self._is_app)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 2804, in relation_get
    raw_data_content = self._run(*args, return_output=True, use_json=True)
  File "/var/lib/juju/agents/unit-self-signed-certificates-2/charm/venv/ops/model.py", line 2725, in _run
    raise ModelError(e.stderr)
ops.model.ModelError: ERROR permission denied