Make InstanceMappings.cell_id nullable

In order to indicate that an instance boot request has been received,
but the instance has not yet been scheduled to a cell, it should be
mapped to a null cell_id. This will mean that an instance list/show will
need to fetch the instance details from the BuildRequest object rather
than looking for the instance in a cell database. A migration is added
and the InstanceMapping object is modified to make this possible.

Partially-implements: bp cells-scheduling-interaction

Change-Id: Iee768512314f11a13e2a85a1e7d5442864ddbc4b

nova/db/sqlalchemy/api_migrations/migrate_repo/versions/007_instance_mapping_nullable_cellid.py

@@ -0,0 +1,22 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from sqlalchemy import MetaData
+from sqlalchemy import Table
+
+
+def upgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    instance_mapping = Table('instance_mappings', meta, autoload=True)
+    instance_mapping.c.cell_id.alter(nullable=True)

nova/db/sqlalchemy/api_models.py

@@ -60,7 +60,7 @@ class InstanceMapping(API_BASE):
     id = Column(Integer, primary_key=True)
     instance_uuid = Column(String(36), nullable=False)
     cell_id = Column(Integer, ForeignKey('cell_mappings.id'),
-            nullable=False)
+            nullable=True)
     project_id = Column(String(255), nullable=False)
 
 

nova/objects/instance_mapping.py

@@ -30,7 +30,7 @@ class InstanceMapping(base.NovaTimestampObject, base.NovaObject,
     fields = {
         'id': fields.IntegerField(read_only=True),
         'instance_uuid': fields.UUIDField(),
-        'cell_id': fields.IntegerField(),
+        'cell_id': fields.IntegerField(nullable=True),
         'project_id': fields.StringField(),
         }
 

nova/tests/functional/db/api/test_migrations.py

@@ -257,6 +257,18 @@ class NovaAPIMigrationsWalk(test_migrations.WalkVersionsMixin):
         self.assertEqual(['id'], fk['referred_columns'])
         self.assertEqual(['request_spec_id'], fk['constrained_columns'])
 
+    def _check_007(self, engine, data):
+        map_table = db_utils.get_table(engine, 'instance_mappings')
+        self.assertTrue(map_table.columns['cell_id'].nullable)
+
+        # Ensure the foreign key still exists
+        inspector = reflection.Inspector.from_engine(engine)
+        # There should only be one foreign key here
+        fk = inspector.get_foreign_keys('instance_mappings')[0]
+        self.assertEqual('cell_mappings', fk['referred_table'])
+        self.assertEqual(['id'], fk['referred_columns'])
+        self.assertEqual(['cell_id'], fk['constrained_columns'])
+
 
 class TestNovaAPIMigrationsWalkSQLite(NovaAPIMigrationsWalk,
                                       test_base.DbTestCase,

nova/tests/functional/db/test_instance_mapping.py

@@ -72,6 +72,10 @@ class InstanceMappingTestCase(test.NoDBTestCase):
                 self.mapping_obj._get_by_instance_uuid_from_db, self.context,
                 mapping['instance_uuid'])
 
+    def test_cell_id_nullable(self):
+        # Just ensure this doesn't raise
+        create_mapping(cell_id=None)
+
 
 class InstanceMappingListTestCase(test.NoDBTestCase):
     def setUp(self):

nova/tests/unit/objects/test_instance_mapping.py

@@ -87,6 +87,11 @@ class _TestInstanceMappingObject(object):
         mapping_obj.destroy()
         destroy_in_db.assert_called_once_with(self.context, uuid)
 
+    def test_cell_id_nullable(self):
+        mapping_obj = objects.InstanceMapping(self.context)
+        # Just ensure this doesn't raise an exception
+        mapping_obj.cell_id = None
+
 
 class TestInstanceMappingObject(test_objects._LocalTest,
                                 _TestInstanceMappingObject):

nova/tests/unit/objects/test_objects.py

@@ -1139,7 +1139,7 @@ object_data = {
     'InstanceGroupList': '1.7-be18078220513316abd0ae1b2d916873',
     'InstanceInfoCache': '1.5-cd8b96fefe0fc8d4d337243ba0bf0e1e',
     'InstanceList': '2.0-6c8ba6147cca3082b1e4643f795068bf',
-    'InstanceMapping': '1.0-47ef26034dfcbea78427565d9177fe50',
+    'InstanceMapping': '1.0-94bff38981ef9ce37c9fccf309b94f58',
     'InstanceMappingList': '1.0-9e982e3de1613b9ada85e35f69b23d47',
     'InstanceNUMACell': '1.3-6991a20992c5faa57fae71a45b40241b',
     'InstanceNUMATopology': '1.2-d944a7d6c21e1c773ffdf09c6d025954',