[DPE 5235] update lib for mongos k8s ext connections (#474)

## Issue
mongos k8s charm handles ext connections by providing a separate port +
ip address

## Solution
update the lib to support this

lib/charms/mongodb/v1/mongodb_provider.py

@@ -31,12 +31,13 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 11
+LIBPATCH = 12
 
 logger = logging.getLogger(__name__)
 REL_NAME = "database"
 MONGOS_RELATIONS = "cluster"
 MONGOS_CLIENT_RELATIONS = "mongos_proxy"
+EXTERNAL_CONNECTIVITY_TAG = "external-node-connectivity"
 
 # We expect the MongoDB container to use the default ports
 
@@ -301,6 +302,10 @@ def _get_config(self, username: str, password: Optional[str]) -> MongoConfigurat
         }
         if self.charm.is_role(Config.Role.MONGOS):
             mongo_args["port"] = Config.MONGOS_PORT
+            if self.substrate == Config.Substrate.K8S:
+                external = self.is_external_client(relation.id)
+                mongo_args["port"] = self.charm.get_mongos_port(external)
+                mongo_args["hosts"] = self.charm.get_mongos_hosts(external)
         else:
             mongo_args["replset"] = self.charm.app.name
 
@@ -396,6 +401,13 @@ def get_relation_name(self):
         else:
             return REL_NAME
 
+    def is_external_client(self, rel_id) -> bool:
+        """Returns true if the integrated client requests external connectivity."""
+        return (
+            self.database_provides.fetch_relation_field(rel_id, EXTERNAL_CONNECTIVITY_TAG)
+            == "true"
+        )
+
     @staticmethod
     def _get_database_from_relation(relation: Relation) -> Optional[str]:
         """Return database name from relation."""

src/charm.py

@@ -419,7 +419,7 @@ def _on_config_changed(self, event: ConfigChangedEvent) -> None:
 
             # TODO in the future (24.04) support migration of components
             logger.error(
-                f"cluster migration currently not supported, cannot change from { self.model.config['role']} to {self.role}"
+                f"cluster migration currently not supported, cannot change from {self.model.config['role']} to {self.role}"
             )
             raise ShardingMigrationError(
                 f"Migration of sharding components not permitted, revert config role to {self.role}"