Make servers API use cell-targeted context

This makes the servers API look up the CellMapping for the instance
in question and target the context to the appropriate cell for the
subsequent call into compute/api.

Note that just as with get() and get_all(), we need to avoid going
direct to the cell database and thus short-circuiting the replication
in the case of cellsv1.

Related to blueprint cells-aware-api
Change-Id: If63a4fa7349890a6e7ac0fa3fe12917dc53334d0

nova/api/openstack/compute/servers.py

@@ -1135,9 +1135,16 @@ class ServersController(wsgi.Controller):
     def _get_instance(self, context, instance_uuid):
         try:
             attrs = ['system_metadata', 'metadata']
-            return objects.Instance.get_by_uuid(context, instance_uuid,
-                                                expected_attrs=attrs)
-        except exception.InstanceNotFound as e:
+            if not CONF.cells.enable:
+                # NOTE(danms): We can't target a cell database if we're
+                # in cellsv1 otherwise we'll short-circuit the replication.
+                mapping = objects.InstanceMapping.get_by_instance_uuid(
+                    context, instance_uuid)
+                nova_context.set_target_cell(context, mapping.cell_mapping)
+            return objects.Instance.get_by_uuid(
+                context, instance_uuid, expected_attrs=attrs)
+        except (exception.InstanceNotFound,
+                exception.InstanceMappingNotFound) as e:
             raise webob.exc.HTTPNotFound(explanation=e.format_message())
 
     @wsgi.response(202)

nova/context.py

@@ -358,19 +358,35 @@ def authorize_quota_class_context(context, class_name):
             raise exception.Forbidden()
 
 
+def set_target_cell(context, cell_mapping):
+    """Adds database connection information to the context
+    for communicating with the given target_cell.
+
+    This is used for permanently targeting a cell in a context.
+    Use this when you want all subsequent code to target a cell.
+
+    :param context: The RequestContext to add connection information
+    :param cell_mapping: An objects.CellMapping object
+    """
+    # avoid circular import
+    from nova import db
+    db_connection_string = cell_mapping.database_connection
+    context.db_connection = db.create_context_manager(db_connection_string)
+
+
 @contextmanager
 def target_cell(context, cell_mapping):
-    """Adds database connection information to the context
+    """Temporarily adds database connection information to the context
     for communicating with the given target cell.
 
+    This context manager makes a temporary change to the context
+    and restores it when complete.
+
     :param context: The RequestContext to add connection information
     :param cell_mapping: A objects.CellMapping object
     """
     original_db_connection = context.db_connection
-    # avoid circular import
-    from nova import db
-    db_connection_string = cell_mapping.database_connection
-    context.db_connection = db.create_context_manager(db_connection_string)
+    set_target_cell(context, cell_mapping)
     try:
         yield context
     finally:

nova/tests/fixtures.py

@@ -291,6 +291,9 @@ class SingleCellSimple(fixtures.Fixture):
         self.useFixture(fixtures.MonkeyPatch(
             'nova.context.target_cell',
             self._fake_target_cell))
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.context.set_target_cell',
+            lambda c, m: None))
 
     def _fake_hostmapping_get(self, *args):
         return {'id': 1,

nova/tests/unit/api/openstack/compute/test_server_start_stop.py

@@ -25,6 +25,7 @@ from nova import db
 from nova import exception
 from nova import policy
 from nova import test
+from nova.tests import fixtures as nova_fixtures
 from nova.tests.unit.api.openstack import fakes
 from nova.tests import uuidsentinel as uuids
 
@@ -35,6 +36,7 @@ class ServerStartStopTestV21(test.TestCase):
         super(ServerStartStopTestV21, self).setUp()
         self._setup_controller()
         self.req = fakes.HTTPRequest.blank('')
+        self.useFixture(nova_fixtures.SingleCellSimple())
         self.stub_out('nova.db.instance_get_by_uuid',
                       fakes.fake_instance_get())
 
@@ -132,6 +134,7 @@ class ServerStartStopPolicyEnforcementV21(test.TestCase):
         self.controller = server_v21.ServersController(
                           extension_info=ext_info)
         self.req = fakes.HTTPRequest.blank('')
+        self.useFixture(nova_fixtures.SingleCellSimple())
         self.stub_out(
             'nova.db.instance_get_by_uuid',
             fakes.fake_instance_get(

nova/tests/unit/api/openstack/compute/test_serversV21.py

@@ -189,6 +189,25 @@ class ServersControllerTest(ControllerTest):
                                        use_admin_context=use_admin_context,
                                        version=self.wsgi_api_version)
 
+    @mock.patch('nova.objects.Instance.get_by_uuid')
+    @mock.patch('nova.objects.InstanceMapping.get_by_instance_uuid')
+    def test_cellsv1_instance_lookup_no_target(self, mock_get_im,
+                                               mock_get_inst):
+        self.flags(enable=True, group='cells')
+        ctxt = context.RequestContext('fake', 'fake')
+        self.controller._get_instance(ctxt, 'foo')
+        self.assertFalse(mock_get_im.called)
+        self.assertIsNone(ctxt.db_connection)
+
+    @mock.patch('nova.objects.Instance.get_by_uuid')
+    @mock.patch('nova.objects.InstanceMapping.get_by_instance_uuid')
+    def test_instance_lookup_targets(self, mock_get_im, mock_get_inst):
+        ctxt = context.RequestContext('fake', 'fake')
+        mock_get_im.return_value.cell_mapping.database_connection = uuids.cell1
+        self.controller._get_instance(ctxt, 'foo')
+        mock_get_im.assert_called_once_with(ctxt, 'foo')
+        self.assertIsNotNone(ctxt.db_connection)
+
     def test_requested_networks_prefix(self):
         self.flags(use_neutron=True)
         uuid = 'br-00000000-0000-0000-0000-000000000000'
@@ -1761,6 +1780,7 @@ class ServersControllerRebuildInstanceTest(ControllerTest):
         self.req.headers["content-type"] = "application/json"
         self.req_user_id = self.req.environ['nova.context'].user_id
         self.req_project_id = self.req.environ['nova.context'].project_id
+        self.useFixture(nova_fixtures.SingleCellSimple())
 
         def fake_get(ctrl, ctxt, uuid):
             if uuid == 'test_inst':