Add regression test for resize failing during retries

During testing in the alternate host series, it was found that retries
when resizing an instance would always fail. This turned out to be true
even before alternate hosts for resize was introduced. Further
investigation showed that there was a race in call to retry the resize
and the revert of the original attempt.

This adds a functional regression test to show the failure. A follow up
patch with the fix will modify the test to show it passing again.

Related-Bug: 1741125

Change-Id: I0760f3e3bc447c39a6443afd7857046a08b8f01d

nova/tests/functional/regressions/test_bug_1741125.py

@@ -0,0 +1,87 @@
+# 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 nova.compute import manager as compute_manager
+from nova.tests.functional.test_servers import ProviderUsageBaseTestCase
+
+
+class TestServerResizeReschedule(ProviderUsageBaseTestCase):
+    """Regression test for bug #1741125
+
+    During testing in the alternate host series, it was found that retries
+    when resizing an instance would always fail. This turned out to be true
+    even before alternate hosts for resize was introduced. Further
+    investigation showed that there was a race in call to retry the resize
+    and the revert of the original attempt.
+
+    This adds a functional regression test to show the failure. A follow up
+    patch with the fix will modify the test to show it passing again.
+    """
+
+    compute_driver = 'fake.SmallFakeDriver'
+
+    def setUp(self):
+        super(TestServerResizeReschedule, self).setUp()
+        self.compute1 = self._start_compute(host='host1')
+        self.compute2 = self._start_compute(host='host2')
+        self.compute3 = self._start_compute(host='host3')
+        self.compute4 = self._start_compute(host='host4')
+
+        flavors = self.api.get_flavors()
+        self.flavor1 = flavors[0]
+        self.flavor2 = flavors[1]
+        if self.flavor1["disk"] > self.flavor2["disk"]:
+            # Make sure that flavor1 is smaller
+            self.flavor1, self.flavor2 = self.flavor2, self.flavor1
+
+    def test_resize_reschedule_uses_host_lists(self):
+        """Test that when a resize attempt fails, the retry comes from the
+        supplied host_list, and does not call the scheduler.
+        """
+        server_req = self._build_minimal_create_server_request(
+                self.api, 'some-server', flavor_id=self.flavor1['id'],
+                image_uuid='155d900f-4e14-4e4c-a73d-069cbf4541e6',
+                networks=[])
+
+        self.first_attempt = True
+        created_server = self.api.post_server({'server': server_req})
+        server = self._wait_for_state_change(self.api, created_server,
+                'ACTIVE')
+
+        actual_prep_resize = compute_manager.ComputeManager._prep_resize
+
+        def fake_prep_resize(*args, **kwargs):
+            if self.first_attempt:
+                # Only fail the first time
+                self.first_attempt = False
+                raise Exception('fake_prep_resize')
+            actual_prep_resize(*args, **kwargs)
+
+        # Yes this isn't great in a functional test, but it's simple.
+        self.stub_out('nova.compute.manager.ComputeManager._prep_resize',
+                      fake_prep_resize)
+
+        server_uuid = server["id"]
+        data = {"resize": {"flavorRef": self.flavor2['id']}}
+        self.api.post_server_action(server_uuid, data)
+
+        # TODO(edleafe): Remove this when the bug is fixed, and uncomment the
+        # block below that relies on the fix.
+        self.assertRaises(AssertionError, self._wait_for_state_change,
+                self.api, created_server, 'VERIFY_RESIZE')
+
+        # Un-comment this when the bug is fixed.
+        # server = self._wait_for_state_change(self.api, created_server,
+        #         'VERIFY_RESIZE')
+        # ctxt = context.get_admin_context()
+        # instance = objects.Instance.get_by_uuid(ctxt, server["id"])
+        # self.assertEqual(int(self.flavor2["id"]), instance.flavor.id)