Make run_instance() bail quietly if instance has been deleted

Right now, we make a big mess in the logs if someone deletes an
instance before we get a chance to run it. This cleans that up
to a single warning message.

Fixes bug 1154292

Change-Id: I2de0c2993d6a16d9482878eee4eef10bfd78c3e6

2 files changed, 22 insertions, 2 deletions

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 53ab3a2ed..b2d69e6a7 100755
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -747,6 +747,15 @@ class ComputeManager(manager.SchedulerDependentManager):
 
         try:
             self._check_instance_exists(context, instance)
+
+            try:
+                self._start_building(context, instance)
+            except exception.InstanceNotFound:
+                LOG.info(_("Instance disappeared before we could start it"),
+                         instance=instance)
+                # Quickly bail out of here
+                return
+
             image_meta = self._check_image_size(context, instance)
 
             if node is None:
@@ -759,8 +768,6 @@ class ComputeManager(manager.SchedulerDependentManager):
             else:
                 extra_usage_info = {}
 
-            self._start_building(context, instance)
-
             self._notify_about_instance_usage(
                     context, instance, "create.start",
                     extra_usage_info=extra_usage_info)
diff --git a/nova/tests/compute/test_compute.py b/nova/tests/compute/test_compute.py
index 0e41678b3..a3ce7bdae 100644
--- a/nova/tests/compute/test_compute.py
+++ b/nova/tests/compute/test_compute.py
@@ -708,6 +708,19 @@ class ComputeTestCase(BaseTestCase):
                           self.compute.run_instance,
                           self.context, instance=instance)
 
+    def test_run_instance_bails_on_missing_instance(self):
+        # Make sure that run_instance() will quickly ignore a deleted instance
+        called = {}
+        instance = self._create_instance()
+
+        def fake_instance_update(self, *a, **args):
+            called['instance_update'] = True
+            raise exception.InstanceNotFound(instance_id='foo')
+        self.stubs.Set(self.compute, '_instance_update', fake_instance_update)
+
+        self.compute.run_instance(self.context, instance)
+        self.assertIn('instance_update', called)
+
     def test_can_terminate_on_error_state(self):
         # Make sure that the instance can be terminated in ERROR state.
         #check failed to schedule --> terminate