[DPE-5325] Only write app data if leader (#676)

* Only write app data if leader

* Unit test

* Cover changes

Author: dragomirp

src/backups.py

@@ -495,8 +495,9 @@ def check_stanza(self) -> None:
         except RetryError as e:
             # If the check command doesn't succeed, remove the stanza name
             # and rollback the configuration.
-            self.charm.app_peer_data.update({"stanza": ""})
-            self.charm.app_peer_data.pop("init-pgbackrest", None)
+            if self.charm.unit.is_leader():
+                self.charm.app_peer_data.update({"stanza": ""})
+                self.charm.app_peer_data.pop("init-pgbackrest", None)
             self.charm.unit_peer_data.update({"stanza": "", "init-pgbackrest": ""})
             self.charm.update_config()
 

tests/unit/test_backups.py

@@ -799,6 +799,33 @@ def test_check_stanza(harness):
         assert _update_config.call_count == 2
         assert _member_started.call_count == 5
         assert _reload_patroni_configuration.call_count == 5
+        assert harness.get_relation_data(peer_rel_id, harness.charm.app) == {
+            "stanza": "test-stanza",
+            "init-pgbackrest": "True",
+        }
+        assert harness.get_relation_data(peer_rel_id, harness.charm.unit) == {}
+        assert isinstance(harness.charm.unit.status, BlockedStatus)
+        assert harness.charm.unit.status.message == FAILED_TO_INITIALIZE_STANZA_ERROR_MESSAGE
+
+        # Test when the archiving is not working correctly (pgBackRest check command fails) on leader.
+        with harness.hooks_disabled():
+            harness.set_leader(True)
+            harness.update_relation_data(
+                peer_rel_id,
+                harness.charm.app.name,
+                {"stanza": "test-stanza", "init-pgbackrest": "True"},
+            )
+            harness.update_relation_data(
+                peer_rel_id,
+                harness.charm.unit.name,
+                {"stanza": "test-stanza", "init-pgbackrest": "True"},
+            )
+        _execute_command.side_effect = ExecError(
+            command=stanza_check_command, exit_code=1, stdout="", stderr="fake error"
+        )
+        _member_started.return_value = True
+        harness.charm.backup.check_stanza()
+        assert _update_config.call_count == 4
         assert harness.get_relation_data(peer_rel_id, harness.charm.app) == {}
         assert harness.get_relation_data(peer_rel_id, harness.charm.unit) == {}
         assert isinstance(harness.charm.unit.status, BlockedStatus)
@@ -807,6 +834,7 @@ def test_check_stanza(harness):
         # Test when the archiving is working correctly (pgBackRest check command succeeds)
         # and the unit is not the leader.
         with harness.hooks_disabled():
+            harness.set_leader(False)
             harness.update_relation_data(
                 peer_rel_id,
                 harness.charm.app.name,