Set BlockedStatus if @ is not used when running `juju config AM con…

…fig_file=@FILE_NAME` (#284)

* set app in BlockedStatus if @ is not used while running juju config

* pin ruff

* update charm_tracing.py lib

* unping ruff

* add example on how to use `config_file` config option

config.yaml

@@ -7,7 +7,12 @@ options:
     default: ""
     description: >
       Alertmanager configuration file (yaml), with the exclusion of the templates section.
-      Refer to https://www.prometheus.io/docs/alerting/latest/configuration/ for full details.
+      To send the contents of a file to this configuration option, the symbol `@` must be used.
+
+      Usage: `juju config alertmanager config_file=@alertmanager.yaml`
+
+      For more information on configuring the Alertmanager, refer to:
+      https://www.prometheus.io/docs/alerting/latest/configuration/
   templates_file:
     type: string
     default: ""

src/charm.py

@@ -351,6 +351,15 @@ def _get_local_config(self) -> Optional[Tuple[Optional[dict], Optional[str]]]:
         config = self.config["config_file"]
         if config:
             local_config = yaml.safe_load(cast(str, config))
+
+            # If `juju config` is executed like this `config_file=am.yaml` instead of
+            # `config_file=@am.yaml` local_config will be the string `am.yaml` instead
+            # of its content (dict).
+            if not isinstance(local_config, dict):
+                msg = f"Unable to set config from file. Use juju config {self.unit.name} config_file=@FILENAME"
+                logger.error(msg)
+                raise ConfigUpdateFailure(msg)
+
             local_templates = cast(str, self.config["templates_file"]) or None
             return local_config, local_templates
         return None

tests/integration/am_config.yaml

@@ -0,0 +1,9 @@
+route:
+  receiver: test_receiver
+  group_by:
+  - alertname
+  group_wait: 1234s
+  group_interval: 4321s
+  repeat_interval: 1111h
+receivers:
+- name: test_receiver

tests/integration/test_remote_configuration.py

@@ -16,6 +16,7 @@
 
 import helpers
 import pytest
+import sh
 import yaml
 from deepdiff import DeepDiff  # type: ignore[import]
 from pytest_operator.plugin import OpsTest
@@ -105,6 +106,26 @@ async def test_remote_configuration_applied_on_relation_created(ops_test: OpsTes
     )
 
 
+@pytest.mark.abort_on_fail
+async def test_remote_configuration_file_wrongly_applied(ops_test: OpsTest, setup):
+    sh.juju(
+        [
+            "config",
+            f"{APP_NAME}",
+            "-m",
+            ops_test.model_name,
+            "config_file=tests/integration/am_config.yaml",
+        ]
+    )
+
+    await ops_test.model.wait_for_idle(
+        apps=[APP_NAME],
+        status="blocked",
+        timeout=1000,
+        idle_period=5,
+    )
+
+
 def _copy_alertmanager_remote_configuration_library_into_tester_charm():
     """Ensure that the tester charm uses the current Alertmanager Remote Configuration library."""
     library_path = "lib/charms/alertmanager_k8s/v0/alertmanager_remote_configuration.py"