fix: use internal UPF hostname when MetalLB is not available (#56)

src/charm.py

@@ -737,25 +737,25 @@ def _get_gnb_subnet_config(self) -> Optional[str]:
     def _get_external_upf_hostname_config(self) -> Optional[str]:
         return self.model.config.get("external-upf-hostname")
 
-    def _upf_load_balancer_service_hostname(self) -> str:
+    def _upf_load_balancer_service_hostname(self) -> Optional[str]:
         """Returns the hostname of UPF's LoadBalancer service.
 
         Returns:
-            str: Hostname of UPF's LoadBalancer service
+            str/None: Hostname of UPF's LoadBalancer service if available else None
         """
         client = Client()
         service = client.get(
             Service, name=f"{self.model.app.name}-external", namespace=self.model.name
         )
         try:
             return service.status.loadBalancer.ingress[0].hostname  # type: ignore[attr-defined]
-        except AttributeError:
+        except (AttributeError, TypeError):
             logger.error(
                 "Service '%s-external' does not have a hostname:\n%s",
                 self.model.app.name,
                 service,
             )
-            return ""
+            return None
 
     @property
     def _upf_hostname(self) -> str:

tests/unit/test_charm.py

@@ -544,6 +544,26 @@ def test_given_external_upf_hostname_config_not_set_and_external_upf_service_hos
             upf_n4_port=TEST_PFCP_PORT,
         )
 
+    @patch("lightkube.core.client.GenericSyncClient", new=Mock)
+    @patch("lightkube.core.client.Client.get")
+    @patch("charms.sdcore_upf.v0.fiveg_n4.N4Provides.publish_upf_n4_information")
+    @patch("charm.PFCP_PORT", TEST_PFCP_PORT)
+    def test_given_external_upf_hostname_config_not_set_and_metallb_not_available_and_fiveg_n4_relation_created_when_fiveg_n4_request_then_upf_hostname_and_n4_port_is_published(  # noqa: E501
+        self, patched_publish_upf_n4_information, patched_lightkube_client_get
+    ):
+        service = Mock(status=Mock(loadBalancer=Mock(ingress=None)))
+        patched_lightkube_client_get.return_value = service
+
+        n4_relation_id = self.harness.add_relation("fiveg_n4", "n4_requirer_app")
+        self.harness.add_relation_unit(n4_relation_id, "n4_requirer_app/0")
+
+        patched_publish_upf_n4_information.assert_called_once_with(
+            relation_id=n4_relation_id,
+            upf_hostname=f"{self.harness.charm.app.name}-external.{self.namespace}"
+            ".svc.cluster.local",
+            upf_n4_port=TEST_PFCP_PORT,
+        )
+
     @patch("charms.sdcore_upf.v0.fiveg_n4.N4Provides.publish_upf_n4_information")
     @patch(f"{MULTUS_LIBRARY_PATH}.KubernetesMultusCharmLib.is_ready")
     @patch(f"{HUGEPAGES_LIBRARY_PATH}.KubernetesHugePagesPatchCharmLib.is_patched")