_update_received_ca_certs method first needs to validate the availability of traefik container

[gatici]

Bug Description

During the integration of CertificateTransfer interface:
If CertificateTransferAvailableEvent is emitted too quick before traefik container become available, _update_received_ca_certs method tries to write to an non-existing path which causes "ops.pebble.ConnectionError: [Errno 2] No such file or directory" error.
In , def _update_received_ca_certs method, first we need to check if container is up or not.

To Reproduce

juju deploy vault-k8s --channel edge -n 5 --trust
juju deploy traefik-k8s --channel edge --trust
juju integrate vault-k8s:send-ca-cert traefik-k8s:receive-ca-cert

Environment

juju: 3.1.5
microk8s: v1.27.5
lxd:5.0.2-838e1b2
certificate_transfer interface: 0.4

Relevant log output

unit-traefik-0: 2023-10-06 12:03:21 DEBUG jujuc running hook tool "state-get" for traefik/0-receive-ca-cert-relation-changed-577932895375089497
unit-traefik-0: 2023-10-06 12:03:21 DEBUG jujuc running hook tool "juju-log" for traefik/0-receive-ca-cert-relation-changed-577932895375089497
unit-traefik-0: 2023-10-06 12:03:21 DEBUG unit.traefik/0.juju-log receive-ca-cert:4: Emitting custom event <CertificateAvailableEvent via TraefikIngressCharm/CertificateTransferRequires[receive-ca-cert]/on/certificate_available[42]>.
unit-traefik-0: 2023-10-06 12:03:21 DEBUG jujuc running hook tool "juju-log" for traefik/0-receive-ca-cert-relation-changed-577932895375089497
unit-traefik-0: 2023-10-06 12:03:21 ERROR unit.traefik/0.juju-log receive-ca-cert:4: Uncaught exception while in charm code:
Traceback (most recent call last):
  File "/usr/lib/python3.8/urllib/request.py", line 1354, in do_open
    h.request(req.get_method(), req.selector, req.data, headers,
  File "/usr/lib/python3.8/http/client.py", line 1256, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1302, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1251, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1011, in _send_output
    self.send(msg)
  File "/usr/lib/python3.8/http/client.py", line 951, in send
    self.connect()
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/pebble.py", line 272, in connect
    self.sock.connect(self.socket_path)
FileNotFoundError: [Errno 2] No such file or directory

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/pebble.py", line 1599, in _request_raw
    response = self.opener.open(request, timeout=self.timeout)
  File "/usr/lib/python3.8/urllib/request.py", line 525, in open
    response = self._open(req, data)
  File "/usr/lib/python3.8/urllib/request.py", line 542, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
  File "/usr/lib/python3.8/urllib/request.py", line 502, in _call_chain
    result = func(*args)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/pebble.py", line 286, in http_open
    return self.do_open(_UnixSocketConnection, req,  # type:ignore
  File "/usr/lib/python3.8/urllib/request.py", line 1357, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [Errno 2] No such file or directory>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./src/charm.py", line 1343, in <module>
    main(TraefikIngressCharm, use_juju_for_storage=True)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/main.py", line 441, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/main.py", line 149, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 342, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 839, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 928, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-traefik-0/charm/lib/charms/certificate_transfer_interface/v0/certificate_transfer.py", line 374, in _on_relation_changed
    self.on.certificate_available.emit(
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 342, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 839, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/framework.py", line 928, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-traefik-0/charm/lib/charms/tempo_k8s/v0/charm_tracing.py", line 455, in wrapped_function
    return callable(*args, **kwargs)  # type: ignore
  File "./src/charm.py", line 271, in _on_recv_ca_cert_available
    self._update_received_ca_certs(event)
  File "/var/lib/juju/agents/unit-traefik-0/charm/lib/charms/tempo_k8s/v0/charm_tracing.py", line 455, in wrapped_function
    return callable(*args, **kwargs)  # type: ignore
  File "./src/charm.py", line 282, in _update_received_ca_certs
    self.container.push(
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/model.py", line 2188, in push
    self._pebble.push(str(path), source, encoding=encoding,
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/pebble.py", line 2014, in push
    response = self._request_raw('POST', '/v1/files', None, headers, data)
  File "/var/lib/juju/agents/unit-traefik-0/charm/venv/ops/pebble.py", line 1612, in _request_raw
    raise ConnectionError(e.reason)
ops.pebble.ConnectionError: [Errno 2] No such file or directory
unit-traefik-0: 2023-10-06 12:03:21 ERROR juju.worker.uniter.operation hook "receive-ca-cert-relation-changed" (via hook dispatching script: dispatch) failed: exit status 1

Additional context

No response

[lucabello]

I believe this is solved by your own PR #267, so I'm closing the issue :)