Override write_leader_optime method in K8s implementation (#2850)

It is being called when postgres is already shut down cleanly but there are no healthy replicas to take it over.

Close https://github.com/zalando/patroni/issues/2837
Close https://github.com/zalando/patroni/pull/2838

patroni/dcs/kubernetes.py

@@ -1140,6 +1140,13 @@ class Kubernetes(AbstractDCS):
         """Unused"""
         raise NotImplementedError  # pragma: no cover
 
+    def write_leader_optime(self, last_lsn: int) -> None:
+        """Write value for WAL LSN to ``optime`` annotation of the leader object.
+
+        :param last_lsn: absolute WAL LSN in bytes.
+        """
+        self.patch_or_create(self.leader_path, {self._OPTIME: str(last_lsn)}, patch=True, retry=False)
+
     def _update_leader_with_retry(self, annotations: Dict[str, Any],
                                   resource_version: Optional[str], ips: List[str]) -> bool:
         retry = self._retry.copy()

tests/test_kubernetes.py

@@ -436,6 +436,10 @@ class TestKubernetesEndpoints(BaseTestKubernetes):
         mock_logger_exception.assert_called_once()
         self.assertEqual(('create_config_service failed',), mock_logger_exception.call_args[0])
 
+    @patch.object(k8s_client.CoreV1Api, 'patch_namespaced_endpoints', mock_namespaced_kind, create=True)
+    def test_write_leader_optime(self):
+        self.k.write_leader_optime(12345)
+
 
 def mock_watch(*args):
     return urllib3.HTTPResponse()