Add regression test for bug 1914777

This adds two tests to cover a regression where racing create and
delete requests could result in a user receiving a 500 error when
attempting to delete an instance:

  Unexpected exception in API method: AttributeError: 'NoneType' object
  has no attribute 'uuid'

Related-Bug: #1914777

NOTE(melwitt): The difference from the cherry picked change is because
I6daea47988181dfa6dde3d9c42004c0ecf6ae87a is not in Ussuri.

Change-Id: I8249c572c6f727ef4ca434843106b9b57c47e585
(cherry picked from commit f7975d640ce1e9fa06d045d35177f07451716f0c)
(cherry picked from commit 4f17ea2f7dedb67802c2a8bc0caa64ff66fd2c9c)

1 files changed, 152 insertions, 0 deletions

diff --git a/nova/tests/functional/regressions/test_bug_1914777.py b/nova/tests/functional/regressions/test_bug_1914777.py
new file mode 100644
index 0000000000..6f5cd92de6
--- /dev/null
+++ b/nova/tests/functional/regressions/test_bug_1914777.py
@@ -0,0 +1,152 @@
+# 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.
+
+import mock
+
+from nova import context as nova_context
+from nova import exception
+from nova import objects
+from nova import test
+from nova.tests import fixtures as nova_fixtures
+from nova.tests.functional.api import client
+from nova.tests.functional import integrated_helpers
+import nova.tests.unit.image.fake
+from nova.tests.unit import policy_fixture
+
+
+class TestDeleteWhileBooting(test.TestCase,
+                             integrated_helpers.InstanceHelperMixin):
+    """This tests race scenarios where an instance is deleted while booting.
+
+    In these scenarios, the nova-api service is racing with nova-conductor
+    service; nova-conductor is in the middle of booting the instance when
+    nova-api begins fulfillment of a delete request. As the two services
+    delete records out from under each other, both services need to handle
+    it properly such that a delete request will always be fulfilled.
+
+    Another scenario where two requests can race and delete things out from
+    under each other is if two or more delete requests are racing while the
+    instance is booting.
+
+    In order to force things into states where bugs have occurred, we must
+    mock some object retrievals from the database to simulate the different
+    points at which a delete request races with a create request or another
+    delete request. We aim to mock only the bare minimum necessary to recreate
+    the bug scenarios.
+    """
+    def setUp(self):
+        super(TestDeleteWhileBooting, self).setUp()
+        self.useFixture(policy_fixture.RealPolicyFixture())
+        self.useFixture(nova_fixtures.NeutronFixture(self))
+        nova.tests.unit.image.fake.stub_out_image_service(self)
+
+        api_fixture = self.useFixture(nova_fixtures.OSAPIFixture(
+            api_version='v2.1'))
+        self.api = api_fixture.api
+
+        self.ctxt = nova_context.get_context()
+
+        # We intentionally do not start a conductor or scheduler service, since
+        # our goal is to simulate an instance that has not been scheduled yet.
+
+        # Kick off a server create request and move on once it's in the BUILD
+        # state. Since we have no conductor or scheduler service running, the
+        # server will "hang" in an unscheduled state for testing.
+        self.server = self._create_server(expected_state='BUILD')
+        # Simulate that a different request has deleted the build request
+        # record after this delete request has begun processing. (The first
+        # lookup of the build request occurs in the servers API to get the
+        # instance object in order to delete it).
+        # We need to get the build request now before we mock the method.
+        self.br = objects.BuildRequest.get_by_instance_uuid(
+            self.ctxt, self.server['id'])
+
+    @mock.patch('nova.objects.build_request.BuildRequest.get_by_instance_uuid')
+    def test_build_request_and_instance_not_found(self, mock_get_br):
+        """This tests a scenario where another request has deleted the build
+        request record and the instance record ahead of us.
+        """
+        # The first lookup at the beginning of the delete request in the
+        # ServersController succeeds and the second lookup to handle "delete
+        # while booting" in compute/api fails after a different request has
+        # deleted it.
+        br_not_found = exception.BuildRequestNotFound(uuid=self.server['id'])
+        mock_get_br.side_effect = [self.br, br_not_found]
+        # FIXME(melwitt): Delete request fails due to the AttributeError.
+        ex = self.assertRaises(
+            client.OpenStackApiException, self._delete_server, self.server)
+        self.assertEqual(500, ex.response.status_code)
+        self.assertIn('AttributeError', str(ex))
+        # FIXME(melwitt): Uncomment when the bug is fixed.
+        # self._delete_server(self.server)
+
+    @mock.patch('nova.objects.build_request.BuildRequest.get_by_instance_uuid')
+    @mock.patch('nova.objects.InstanceMapping.get_by_instance_uuid')
+    @mock.patch('nova.objects.instance.Instance.get_by_uuid')
+    def test_deleting_instance_at_the_same_time(self, mock_get_i, mock_get_im,
+                                                mock_get_br):
+        """This tests the scenario where another request is trying to delete
+        the instance record at the same time we are, while the instance is
+        booting. An example of this: while the create and delete are running at
+        the same time, the delete request deletes the build request, the create
+        request finds the build request already deleted when it tries to delete
+        it. The create request deletes the instance record and then delete
+        request tries to lookup the instance after it deletes the build
+        request. Its attempt to lookup the instance fails because the create
+        request already deleted it.
+        """
+        # First lookup at the beginning of the delete request in the
+        # ServersController succeeds, second lookup to handle "delete while
+        # booting" in compute/api fails after the conductor has deleted it.
+        br_not_found = exception.BuildRequestNotFound(uuid=self.server['id'])
+        mock_get_br.side_effect = [self.br, br_not_found]
+        # Simulate the instance transitioning from having no cell assigned to
+        # having a cell assigned while the delete request is being processed.
+        # First lookup of the instance mapping has the instance unmapped (no
+        # cell) and subsequent lookups have the instance mapped to cell1.
+        no_cell_im = objects.InstanceMapping(
+            context=self.ctxt, instance_uuid=self.server['id'],
+            cell_mapping=None)
+        has_cell_im = objects.InstanceMapping(
+            context=self.ctxt, instance_uuid=self.server['id'],
+            cell_mapping=self.cell_mappings['cell1'])
+        mock_get_im.side_effect = [
+            no_cell_im, has_cell_im, has_cell_im, has_cell_im]
+        # Simulate that the instance object has been created by the conductor
+        # in the create path while the delete request is being processed.
+        # First lookups are before the instance has been deleted and the last
+        # lookup is after the conductor has deleted the instance. Use the build
+        # request to make an instance object for testing.
+        i = self.br.get_new_instance(self.ctxt)
+        i_not_found = exception.InstanceNotFound(instance_id=self.server['id'])
+        mock_get_i.side_effect = [i, i, i, i_not_found]
+
+        # Simulate that the conductor is running instance_destroy at the same
+        # time as we are.
+        def fake_instance_destroy(*args, **kwargs):
+            # NOTE(melwitt): This is a misleading exception, as it is not only
+            # raised when a constraint on 'host' is not met, but also when two
+            # instance_destroy calls are racing. In this test, the soft delete
+            # returns 0 rows affected because another request soft deleted the
+            # record first.
+            raise exception.ObjectActionError(
+                action='destroy', reason='host changed')
+
+        self.stub_out(
+            'nova.objects.instance.Instance.destroy', fake_instance_destroy)
+        # FIXME(melwitt): Delete request fails due to the AttributeError.
+        ex = self.assertRaises(
+            client.OpenStackApiException, self._delete_server, self.server)
+        self.assertEqual(500, ex.response.status_code)
+        self.assertIn('AttributeError', str(ex))
+        # FIXME(melwitt): Uncomment when the bug is fixed.
+        # self._delete_server(self.server)