SoftwareDeploymentGroup allow arbitrary keys for attributes

Since SoftwareDeploymentGroup is really a ResourceGroup, it's capable
of resolving any attribute supported by SoftwareDeployment, including
arbitrary outputs mapped to attributes.  Exposing these via the
SoftwareDeploymentGroup resource provides much better flexibility than
forcing users to mangle everything via stdout.

This has the side-effect of making the existing attributes somewhat
redundant, e.g:

get_attr: [a_sdg, deploy_stdouts]

is exactly equivalent to this:

get_attr: [a_sdg, deploy_stdout]

The deploy_stdout attribute should be transparently reflected from the
SoftwareDeployment resources via the normal ResourceGroup interfaces,
so we could consider deprecating the existing attributes at some point.

Change-Id: Ie3b89155d2be0050394eb7f7d5000331cde9aae0
Closes-Bug: #1488921

heat/engine/resources/openstack/heat/software_deployment.py

@@ -548,6 +548,16 @@ class SoftwareDeployment(signal_responder.SignalResponder):
 
 
 class SoftwareDeploymentGroup(resource_group.ResourceGroup):
+    '''
+    This resource associates a group of servers with some configuration which
+    is to be deployed to all servers in the group.
+
+    The properties work in a similar way to OS::Heat::SoftwareDeployment,
+    and in addition to the attributes documented, you may pass any
+    attribute supported by OS::Heat::SoftwareDeployment, including those
+    exposing arbitrary outputs, and return a map of deployment names to
+    the specified attribute.
+    '''
 
     support_status = support.SupportStatus(version='5.0.0')
 
@@ -644,7 +654,9 @@ class SoftwareDeploymentGroup(resource_group.ResourceGroup):
         elif key == self.STATUS_CODES:
             n_attr = SoftwareDeployment.STATUS_CODE
         else:
-            return None
+            # Allow any attribute valid for a single SoftwareDeployment
+            # including arbitrary outputs, so we can't validate here
+            n_attr = key
 
         rg_attr = rg.FnGetAtt(rg.ATTR_ATTRIBUTES, n_attr)
         return attributes.select_from_attribute(rg_attr, path)

heat/tests/test_software_deployment.py

@@ -1333,6 +1333,34 @@ class SoftwareDeploymentGroupTest(common.HeatTestCase):
             mock.call('deploy_status_code'),
         ])
 
+    def test_attributes_passthrough_key(self):
+        '''Prove attributes not in the schema pass-through.'''
+        stack = utils.parse_stack(self.template)
+        snip = stack.t.resource_definitions(stack)['deploy_mysql']
+        resg = sd.SoftwareDeploymentGroup('test', snip, stack)
+        nested = self.patchobject(resg, 'nested')
+        server1 = mock.MagicMock()
+        server2 = mock.MagicMock()
+        nested.return_value = {
+            'server1': server1,
+            'server2': server2
+        }
+
+        server1.FnGetAtt.return_value = 'attr1'
+        server2.FnGetAtt.return_value = 'attr2'
+        self.assertEqual({
+            'server1': 'attr1',
+            'server2': 'attr2'
+        }, resg.FnGetAtt('some_attr'))
+
+        server1.FnGetAtt.assert_has_calls([
+            mock.call('some_attr'),
+        ])
+
+        server2.FnGetAtt.assert_has_calls([
+            mock.call('some_attr'),
+        ])
+
     def test_validate(self):
         stack = utils.parse_stack(self.template)
         snip = stack.t.resource_definitions(stack)['deploy_mysql']