Send events from PrometheusRemoteWriteProvider (#440)

lib/charms/prometheus_k8s/v0/prometheus_remote_write.py

@@ -45,7 +45,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 10
+LIBPATCH = 11
 
 
 logger = logging.getLogger(__name__)
@@ -721,6 +721,33 @@ def endpoints(self) -> List[Dict[str, str]]:
         return endpoints
 
 
+class PrometheusRemoteWriteAlertsChangedEvent(EventBase):
+    """Event emitted when Prometheus remote_write alerts change."""
+
+    def __init__(self, handle, relation_id):
+        super().__init__(handle)
+        self.relation_id = relation_id
+
+    def snapshot(self):
+        """Save Prometheus remote_write information."""
+        return {"relation_id": self.relation_id}
+
+    def restore(self, snapshot):
+        """Restore Prometheus remote_write information."""
+        self.relation_id = snapshot["relation_id"]
+
+
+class PrometheusRemoteWriteProviderConsumersChangedEvent(EventBase):
+    """Event emitted when Prometheus remote_write alerts change."""
+
+
+class PrometheusRemoteWriteProviderEvents(ObjectEvents):
+    """Event descriptor for events raised by `PrometheusRemoteWriteProvider`."""
+
+    alert_rules_changed = EventSource(PrometheusRemoteWriteAlertsChangedEvent)
+    consumers_changed = EventSource(PrometheusRemoteWriteProviderConsumersChangedEvent)
+
+
 class PrometheusRemoteWriteProvider(Object):
     """API that manages a provided `prometheus_remote_write` relation.
 
@@ -760,6 +787,8 @@ def __init__(self, *args):
     name to differentiate between "incoming" and "outgoing" remote write interactions is necessary.
     """
 
+    on = PrometheusRemoteWriteProviderEvents()
+
     def __init__(
         self,
         charm: CharmBase,
@@ -810,15 +839,25 @@ def __init__(
         on_relation = self._charm.on[self._relation_name]
         self.framework.observe(
             on_relation.relation_created,
-            self._on_relation_change,
+            self._on_consumers_changed,
         )
         self.framework.observe(
             on_relation.relation_joined,
-            self._on_relation_change,
+            self._on_consumers_changed,
         )
+        self.framework.observe(
+            on_relation.relation_changed,
+            self._on_relation_changed,
+        )
+
+    def _on_consumers_changed(self, event: RelationEvent) -> None:
+        if not isinstance(event, RelationBrokenEvent):
+            self.update_endpoint(event.relation)
+        self.on.consumers_changed.emit()
 
-    def _on_relation_change(self, event: RelationEvent) -> None:
-        self.update_endpoint(event.relation)
+    def _on_relation_changed(self, event: RelationEvent) -> None:
+        """Flag Providers that data has changed so they can re-read alerts."""
+        self.on.alert_rules_changed.emit(event.relation.id)
 
     def update_endpoint(self, relation: Optional[Relation] = None) -> None:
         """Triggers programmatically the update of the relation data.

src/charm.py

@@ -163,9 +163,8 @@ def __init__(self, *args):
         self.framework.observe(self.on.update_status, self._update_status)
         self.framework.observe(self.ingress.on.ready_for_unit, self._on_ingress_ready)
         self.framework.observe(self.ingress.on.revoked_for_unit, self._on_ingress_revoked)
-        self.framework.observe(self.on.receive_remote_write_relation_created, self._configure)
-        self.framework.observe(self.on.receive_remote_write_relation_changed, self._configure)
-        self.framework.observe(self.on.receive_remote_write_relation_broken, self._configure)
+        self.framework.observe(self.remote_write_provider.on.alert_rules_changed, self._configure)
+        self.framework.observe(self.remote_write_provider.on.consumers_changed, self._configure)
         self.framework.observe(self.metrics_consumer.on.targets_changed, self._configure)
         self.framework.observe(self.alertmanager_consumer.on.cluster_changed, self._configure)
         self.framework.observe(self.resources_patch.on.patch_failed, self._on_k8s_patch_failed)