Merge pull request #339 from canonical/backport-handle-relation-broken

backport(fix): Handle relation-broken events (#272)

charms/kfp-api/src/charm.py

@@ -483,7 +483,15 @@ def _get_relational_db_data(self) -> dict:
         self._get_db_relation("relational-db")
 
         # retrieve database data from library
-        relation_data = self.database.fetch_relation_data()
+        try:
+            # if called in response to a '*-relation-broken' event, this will raise an exception
+            relation_data = self.database.fetch_relation_data()
+        except KeyError:
+            self.logger.error("Failed to retrieve relation data from library")
+            raise GenericCharmRuntimeError(
+                "Failed to retrieve relational-db data. This is to be expected if executed in"
+                " response to a '*-relation-broken' event"
+            )
         # parse data in relation
         # this also validates expected data by means of KeyError exception
         for val in relation_data.values():

charms/kfp-api/tests/integration/test_charm.py

@@ -174,6 +174,9 @@ async def test_msql_relation_with_relational_db_relation(self, ops_test: OpsTest
         )
         assert ops_test.model.applications[APP_NAME].units[0].workload_status == "blocked"
 
+        # remove redundant relation
+        await ops_test.juju("remove-relation", f"{APP_NAME}:mysql", "kfp-db:mysql")
+
     async def test_prometheus_grafana_integration(self, ops_test: OpsTest):
         """Deploy prometheus, grafana and required relations, then test the metrics."""
         prometheus = "prometheus-k8s"
@@ -240,3 +243,8 @@ async def test_prometheus_grafana_integration(self, ops_test: OpsTest):
         wait=wait_exponential(multiplier=1, min=1, max=10),
         reraise=True,
     )
+
+    async def test_remove_application(self, ops_test: OpsTest):
+        """Test that the application can be removed successfully."""
+        await ops_test.model.remove_application(app_name=APP_NAME, block_until_done=True)
+        assert APP_NAME not in ops_test.model.applications

charms/kfp-api/tests/unit/test_operator.py

@@ -6,11 +6,13 @@
 
 import pytest
 import yaml
-from ops.model import ActiveStatus, BlockedStatus, WaitingStatus
+from ops.model import ActiveStatus, BlockedStatus, MaintenanceStatus, WaitingStatus
 from ops.testing import Harness
 
 from charm import ErrorWithStatus, KfpApiOperator
 
+KFP_API_CONTAINER_NAME = "apiserver"
+
 
 @pytest.fixture()
 def mocked_resource_handler(mocker):
@@ -570,3 +572,39 @@ def test_relational_db_relation_with_data(
                 "db_host": "host",
                 "db_port": "1234",
             }
+
+    def test_relational_db_relation_broken(
+        self,
+        mocked_resource_handler,
+        mocked_lightkube_client,
+        mocked_kubernetes_service_patcher,
+        harness: Harness,
+    ):
+        """Test that a relation broken event is properly handled."""
+        database = MagicMock()
+        fetch_relation_data = MagicMock(side_effect=KeyError())
+        database.fetch_relation_data = fetch_relation_data
+        harness.model.get_relation = MagicMock(
+            side_effect=self._get_relation_db_only_side_effect_func
+        )
+
+        rel_name = "relational-db"
+        rel_id = harness.add_relation(rel_name, "relational-db-provider")
+
+        harness.begin()
+        harness.set_leader(True)
+        harness.container_pebble_ready(KFP_API_CONTAINER_NAME)
+
+        assert harness.model.unit.status == WaitingStatus("Waiting for relational-db data")
+
+        harness.charm.database = database
+        del harness.model.get_relation
+
+        harness._emit_relation_broken(rel_name, rel_id, "kfp-api")
+
+        assert harness.model.unit.status == BlockedStatus(
+            "Please add required database relation: eg. relational-db"
+        )
+
+        harness.charm.on.remove.emit()
+        assert harness.model.unit.status == MaintenanceStatus("K8S resources removed")