Enhance StackResource update for more use cases

Enhance StackResource.update_with_template to accommodate more
possible use cases. This will take care of the nested stack update
failure by raising an exception in such case, so the the concrete
nested stack resource implementations will have a chance to take
some actions upon nested stack update failure.

blueprint nested-stack-updates

Change-Id: Id31ef67e1d7c4928704c6e169bce13f0f7232932

heat/engine/resources/autoscaling.py

@@ -174,12 +174,15 @@ class InstanceGroup(stack_resource.StackResource):
         When shrinking, the newest instances will be removed.
         """
         new_template = self._create_template(new_capacity)
-        result = self.update_with_template(new_template, {})
-        for resource in self.nested():
-            if resource.state == ('CREATE', 'FAILED'):
-                resource.destroy()
+        try:
+            self.update_with_template(new_template, {})
+        except exception.Error as ex:
+            logger.error('Failed to resize instance group %s. Error: %s' %
+                         (self.name, ex))
+            for resource in self.nested():
+                if resource.state == ('CREATE', 'FAILED'):
+                    resource.destroy()
         self._lb_reload()
-        return result
 
     def _lb_reload(self):
         '''

heat/engine/stack_resource.py

@@ -113,9 +113,25 @@ class StackResource(resource.Resource):
                              environment.Environment(user_params),
                              timeout_mins=timeout_mins,
                              disable_rollback=True,
-                             parent_resource=self)
+                             parent_resource=self,
+                             owner_id=self.stack.id)
         stack.validate()
-        return self._nested.update(stack)
+
+        nested_stack = self.nested()
+        if nested_stack is None:
+            raise exception.Error(_('Cannot update %s, stack not created')
+                                  % self.name)
+
+        if not hasattr(type(self), 'attributes_schema'):
+            self.attributes = None
+            self._outputs_to_attribs(child_template)
+
+        nested_stack.update(stack)
+
+        if nested_stack.state != (nested_stack.UPDATE,
+                                  nested_stack.COMPLETE):
+            raise exception.Error("Nested stack update failed: %s" %
+                                  nested_stack.status_reason)
 
     def delete_nested(self):
         '''

heat/tests/test_stack_resource.py

@@ -12,6 +12,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+
+import mox
+
 from heat.common import template_format
 from heat.common import exception
 from heat.engine import environment
@@ -167,6 +170,35 @@ class StackResourceTest(HeatTestCase):
             self.parent_stack.context, self.stack.id)
         self.assertEqual(saved_stack.owner_id, self.parent_stack.id)
 
+    @utils.stack_delete_after
+    def test_update_with_template_state_err(self):
+        """
+        update_with_template_state_err method should raise error when update
+        task is done but the nested stack is in (UPDATE, FAILED) state.
+        """
+        create_creator = self.parent_resource.create_with_template(
+            self.simple_template, {})
+        create_creator.run_to_completion()
+        self.stack = self.parent_resource.nested()
+
+        new_templ = self.simple_template.copy()
+        inst_snippet = new_templ["Resources"]["WebServer"].copy()
+        new_templ["Resources"]["WebServer2"] = inst_snippet
+
+        def change_state(stack):
+            self.stack.state_set(parser.Stack.UPDATE, parser.Stack.FAILED, '')
+
+        self.m.StubOutWithMock(self.stack, 'update')
+        self.stack.update(mox.IgnoreArg()).WithSideEffects(change_state)
+        self.m.ReplayAll()
+
+        try:
+            self.parent_resource.update_with_template(new_templ, {})
+        except exception.Error as ex:
+            self.assertEqual('Nested stack update failed: ', ex.message)
+
+        self.m.VerifyAll()
+
     @utils.stack_delete_after
     def test_load_nested_ok(self):
         self.parent_resource.create_with_template(self.templ,