Make scheduler lazy-load the placement client

Like we did for conductor, this makes the scheduler lazy-load the
placement client instead of only doing it during __init__. This avoids
a startup crash if keystone or placement are not available, but
retains startup failures for other problems and errors likely to be
a result of misconfigurations.

Closes-Bug: #2012530
Change-Id: I42ed876b84d80536e83d9ae01696b0a64299c9f7

nova/scheduler/manager.py

@@ -23,6 +23,7 @@ import collections
 import copy
 import random
 
+from keystoneauth1 import exceptions as ks_exc
 from oslo_log import log as logging
 import oslo_messaging as messaging
 from oslo_serialization import jsonutils
@@ -67,10 +68,42 @@ class SchedulerManager(manager.Manager):
         self.host_manager = host_manager.HostManager()
         self.servicegroup_api = servicegroup.API()
         self.notifier = rpc.get_notifier('scheduler')
-        self.placement_client = report.report_client_singleton()
+        self._placement_client = None
+
+        try:
+            # Test our placement client during initialization
+            self.placement_client
+        except (ks_exc.EndpointNotFound,
+                ks_exc.DiscoveryFailure,
+                ks_exc.RequestTimeout,
+                ks_exc.GatewayTimeout,
+                ks_exc.ConnectFailure) as e:
+            # Non-fatal, likely transient (although not definitely);
+            # continue startup but log the warning so that when things
+            # fail later, it will be clear why we can not do certain
+            # things.
+            LOG.warning('Unable to initialize placement client (%s); '
+                        'Continuing with startup, but scheduling '
+                        'will not be possible.', e)
+        except (ks_exc.MissingAuthPlugin,
+                ks_exc.Unauthorized) as e:
+            # This is almost definitely fatal mis-configuration. The
+            # Unauthorized error might be transient, but it is
+            # probably reasonable to consider it fatal.
+            LOG.error('Fatal error initializing placement client; '
+                      'config is incorrect or incomplete: %s', e)
+            raise
+        except Exception as e:
+            # Unknown/unexpected errors here are fatal
+            LOG.error('Fatal error initializing placement client: %s', e)
+            raise
 
         super().__init__(service_name='scheduler', *args, **kwargs)
 
+    @property
+    def placement_client(self):
+        return report.report_client_singleton()
+
     @periodic_task.periodic_task(
         spacing=CONF.scheduler.discover_hosts_in_cells_interval,
         run_immediately=True)

nova/tests/unit/scheduler/test_manager.py

@@ -19,6 +19,7 @@ Tests For Scheduler
 
 from unittest import mock
 
+from keystoneauth1 import exceptions as ks_exc
 import oslo_messaging as messaging
 from oslo_serialization import jsonutils
 from oslo_utils.fixture import uuidsentinel as uuids
@@ -1688,6 +1689,41 @@ class SchedulerManagerTestCase(test.NoDBTestCase):
         mock_log_warning.assert_not_called()
         mock_log_debug.assert_called_once_with(msg)
 
+    @mock.patch('nova.scheduler.client.report.report_client_singleton')
+    @mock.patch.object(manager, 'LOG')
+    @mock.patch('nova.scheduler.host_manager.HostManager')
+    @mock.patch('nova.servicegroup.API')
+    @mock.patch('nova.rpc.get_notifier')
+    def test_init_lazy_placement_client(self, mock_rpc, mock_sg, mock_hm,
+                                        mock_log, mock_report):
+        # Simulate keytone or placement being offline at startup
+        mock_report.side_effect = ks_exc.RequestTimeout
+        mgr = manager.SchedulerManager()
+        mock_report.assert_called_once_with()
+        self.assertTrue(mock_log.warning.called)
+
+        # Make sure we're raising the actual error to subsequent callers
+        self.assertRaises(ks_exc.RequestTimeout, lambda: mgr.placement_client)
+
+        # Simulate recovery of the keystone or placement service
+        mock_report.reset_mock(side_effect=True)
+        mgr.placement_client
+        mock_report.assert_called_once_with()
+
+    @mock.patch('nova.scheduler.client.report.report_client_singleton')
+    @mock.patch('nova.scheduler.host_manager.HostManager')
+    @mock.patch('nova.servicegroup.API')
+    @mock.patch('nova.rpc.get_notifier')
+    def test_init_lazy_placement_client_failures(self, mock_rpc, mock_sg,
+                                                 mock_hm, mock_report):
+        # Certain keystoneclient exceptions are fatal
+        mock_report.side_effect = ks_exc.Unauthorized
+        self.assertRaises(ks_exc.Unauthorized, manager.SchedulerManager)
+
+        # Anything else is fatal
+        mock_report.side_effect = test.TestingException
+        self.assertRaises(test.TestingException, manager.SchedulerManager)
+
 
 class SchedulerManagerAllocationCandidateTestCase(test.NoDBTestCase):