All units receive config-changed when application config changes

kepler/src/charm.py

@@ -31,6 +31,7 @@ def __init__(self, framework: ops.Framework) -> None:
         super().__init__(framework)
         self.pebble_service_name = "fastapi-service"
         framework.observe(self.on["demo-server"].pebble_ready, self._on_demo_server_pebble_ready)
+        framework.observe(self.on.config_changed, self._on_config_changed)
 
     def _on_demo_server_pebble_ready(self, event: ops.PebbleReadyEvent) -> None:
         """Define and start a workload using the Pebble API."""
@@ -40,9 +41,18 @@ def _on_demo_server_pebble_ready(self, event: ops.PebbleReadyEvent) -> None:
         container.add_layer("fastapi_demo", self._get_pebble_layer(), combine=True)
         # Make Pebble reevaluate its plan, ensuring any services are started if enabled.
         container.replan()
-        # Learn more about statuses at
-        # https://documentation.ubuntu.com/juju/3.6/reference/status/
-        self.unit.status = ops.ActiveStatus()
+        # Reflect the current config in the unit status so that a config-changed
+        # event on this unit is observable via `juju status`.
+        self._update_status()
+
+    def _on_config_changed(self, event: ops.ConfigChangedEvent) -> None:
+        """Update the unit status to reflect the current log-level config."""
+        self._update_status()
+
+    def _update_status(self) -> None:
+        """Set the unit status to an active status reporting the log-level config."""
+        log_level = self.config.get("log-level", "info")
+        self.unit.status = ops.ActiveStatus(f"log-level={log_level}")
 
     def _get_pebble_layer(self) -> ops.pebble.Layer:
         """Pebble layer for the FastAPI demo services."""

kepler/tests/integration/test_charm.py

@@ -31,11 +31,56 @@
 APP_NAME = METADATA["name"]
 
 
+def _all_units_report(status: jubilant.Status, app: str, message: str) -> bool:
+    """Report whether every unit of *app* is active with the given workload status message.
+
+    This is used as a ``juju.wait`` ready condition so that the wait does not return until the
+    config-changed event has actually been processed on every unit and the status message
+    updated — not merely until the units are idle.
+    """
+    app_info = status.apps.get(app)
+    if app_info is None:
+        return False
+    if app_info.app_status.current != "active":
+        return False
+    if not app_info.units:
+        return False
+    for unit in app_info.units.values():
+        if unit.workload_status.current != "active":
+            return False
+        if unit.workload_status.message != message:
+            return False
+    return True
+
+
 @pytest.mark.juju_setup
 def test_deploy(charm: pathlib.Path, juju: jubilant.Juju):
-    """Deploy the charm under test."""
+    """Deploy the charm under test with two units."""
     resources = {
         "demo-server-image": METADATA["resources"]["demo-server-image"]["upstream-source"]
     }
-    juju.deploy(charm, app=APP_NAME, resources=resources)
+    juju.deploy(charm, app=APP_NAME, resources=resources, num_units=2)
     juju.wait(jubilant.all_active)
+
+
+def test_all_units_get_config_changed(juju: jubilant.Juju):
+    """Verify that a config change fires config-changed on every unit, not just the leader.
+
+    The charm sets its unit status to ``log-level=<value>`` in the config-changed handler.
+    After changing the ``log-level`` config, every unit's workload status message should
+    reflect the new value. If only the leader received config-changed, the non-leader unit
+    would still show the old value.
+    """
+    expected = "log-level=debug"
+    juju.config(APP_NAME, {"log-level": "debug"})
+    juju.wait(lambda status: _all_units_report(status, APP_NAME, expected))
+
+    status = juju.status()
+    units = status.apps[APP_NAME].units
+    assert len(units) == 2, f"expected 2 units, got {len(units)}"
+
+    for unit_name, unit in units.items():
+        message = unit.workload_status.message
+        assert message == expected, (
+            f"unit {unit_name} did not get config-changed: status message is {message!r}"
+        )

kepler/tests/unit/test_charm.py

@@ -44,10 +44,42 @@ def test_pebble_layer():
 
     # Check that we have the plan we expected:
     assert state_out.get_container(container.name).plan == expected_plan
-    # Check the unit is active:
-    assert state_out.unit_status == testing.ActiveStatus()
+    # Check the unit is active and reports the default log-level:
+    assert state_out.unit_status == testing.ActiveStatus("log-level=info")
     # Check the service was started:
     assert (
         state_out.get_container(container.name).service_statuses["fastapi-service"]
         == ops.pebble.ServiceStatus.ACTIVE
     )
+
+
+def test_config_changed_updates_status():
+    """A config-changed event updates the unit status to reflect the new log-level."""
+    ctx = testing.Context(KosmosCharm)
+    container = testing.Container(name="demo-server", can_connect=True)
+    state_in = testing.State(
+        containers={container},
+        leader=True,
+        config={"log-level": "debug"},
+    )
+    state_out = ctx.run(ctx.on.config_changed(), state_in)
+    assert state_out.unit_status == testing.ActiveStatus("log-level=debug")
+
+
+def test_config_changed_survives_pebble_ready():
+    """The status set by config-changed survives a subsequent pebble-ready event.
+
+    This mirrors the real event sequence on a unit: config-changed and pebble-ready
+    both fire during the initial deploy, and both handlers set the status from the
+    same config value, so the observable is preserved across the full sequence.
+    """
+    ctx = testing.Context(KosmosCharm)
+    container = testing.Container(name="demo-server", can_connect=True)
+    state = testing.State(
+        containers={container},
+        leader=True,
+        config={"log-level": "debug"},
+    )
+    state = ctx.run(ctx.on.config_changed(), state)
+    state = ctx.run(ctx.on.pebble_ready(container), state)
+    assert state.unit_status == testing.ActiveStatus("log-level=debug")