update charms.traefik_route_k8s.v0.traefik_route library

lib/charms/traefik_route_k8s/v0/traefik_route.py

@@ -88,7 +88,7 @@ def __init__(self, *args):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 3
+LIBPATCH = 2
 
 log = logging.getLogger(__name__)
 
@@ -148,7 +148,7 @@ def __init__(
         super().__init__(charm, relation_name)
         self._stored.set_default(external_host=None)
 
-        self.charm = charm
+        self._charm = charm
         self._relation_name = relation_name
 
         if self._stored.external_host != external_host:
@@ -157,9 +157,31 @@ def __init__(
             self._update_requirers_with_external_host()
 
         self.framework.observe(
-            self.charm.on[relation_name].relation_changed, self._on_relation_changed
+            self._charm.on[relation_name].relation_changed, self._on_relation_changed
         )
 
+    @property
+    def external_host(self) -> str:
+        """Return the external host set by Traefik, if any."""
+        self._update_stored_external_host()
+        return self._stored.external_host or ""
+
+    def _update_stored_external_host(self) -> None:
+        """Ensure that the stored host is up to date.
+
+        This is split out into a separate method since, in the case of multi-unit deployments,
+        removal of a `TraefikRouteRequirer` will not cause a `RelationEvent`, but the guard on
+        app data ensures that only the previous leader will know what it is. Separating it
+        allows for re-use both when the property is called and if the relation changes, so a
+        leader change where the new leader checks the property will do the right thing."""
+        if self._charm.unit.is_leader():
+            for relation in self._charm.model.relations[self._relation_name]:
+                if not relation.app:
+                    self._stored.external_host = ""
+                    return
+                external_host = relation.data[relation.app].get("external_host", "")
+                self._stored.external_host = external_host or self._stored.external_host
+
     def _on_relation_changed(self, event: RelationEvent):
         if self.is_ready(event.relation):
             # todo check data is valid here?
@@ -168,11 +190,11 @@ def _on_relation_changed(self, event: RelationEvent):
 
     def _update_requirers_with_external_host(self):
         """Ensure that requirers know the external host for Traefik."""
-        if not self.charm.unit.is_leader():
+        if not self._charm.unit.is_leader():
             return
 
-        for relation in self.charm.model.relations[self._relation_name]:
-            relation.data[self.charm.app]["external_host"] = self._stored.external_host
+        for relation in self._charm.model.relations[self._relation_name]:
+            relation.data[self._charm.app]["external_host"] = self.external_host
 
     @staticmethod
     def is_ready(relation: Relation) -> bool:
@@ -213,6 +235,9 @@ def __init__(self, charm: CharmBase, relation: Relation, relation_name: str = "t
         self.framework.observe(
             self._charm.on[relation_name].relation_changed, self._on_relation_changed
         )
+        self.framework.observe(
+            self._charm.on[relation_name].relation_broken, self._on_relation_broken
+        )
 
     @property
     def external_host(self) -> str:
@@ -231,6 +256,9 @@ def _update_stored_external_host(self) -> None:
         if self._charm.unit.is_leader():
             if self._relation:
                 for relation in self._charm.model.relations[self._relation.name]:
+                    if not relation.app:
+                        self._stored.external_host = ""
+                        return
                     external_host = relation.data[relation.app].get("external_host", "")
                     self._stored.external_host = external_host or self._stored.external_host
 
@@ -240,6 +268,12 @@ def _on_relation_changed(self, event: RelationEvent) -> None:
         if self._charm.unit.is_leader():
             self.on.ready.emit(event.relation)
 
+    def _on_relation_broken(self, event: RelationEvent) -> None:
+        """On RelationBroken, clear the stored data if set and emit an event."""
+        self._stored.external_host = ""
+        if self._charm.unit.is_leader():
+            self.on.ready.emit(event.relation)
+
     def is_ready(self) -> bool:
         """Is the TraefikRouteRequirer ready to submit data to Traefik?"""
         return self._relation is not None