feat(release): throw 409 when identical release is done sequantially

This replaces logging that nothing changed for the release and still going ahead with the release. Now it is a noop operation.

Fixes #321

rootfs/api/models/release.py

@@ -5,7 +5,8 @@
 
 from registry import publish_release, get_port as docker_get_port, RegistryException
 from api.utils import dict_diff
-from api.models import UuidAuditedModel, DeisException
+from api.models import UuidAuditedModel
+from api.exceptions import DeisException, AlreadyExists
 from scheduler import KubeHTTPException
 
 logger = logging.getLogger(__name__)
@@ -423,5 +424,7 @@ def save(self, *args, **kwargs):  # noqa
                 if self.version == 1:
                     self.summary = "{} created the initial release".format(self.owner)
                 else:
-                    self.summary = "{} changed nothing".format(self.owner)
+                    # There were no changes to this release
+                    raise AlreadyExists("{} changed nothing - release stopped".format(self.owner))
+
         super(Release, self).save(*args, **kwargs)

rootfs/api/tests/test_release.py

@@ -349,3 +349,27 @@ def test_release_unset_config(self, mock_requests):
         body = {'cpu': json.dumps({'cmd': None})}
         response = self.client.post(url, body)
         self.assertEqual(response.status_code, 422, response.data)
+
+    def test_release_no_change(self, mock_requests):
+        """
+        Test that a release is created when an app is created, and
+        then has 2 identical config set, causing a 409 as there was
+        no change
+        """
+        url = '/v2/apps'
+        response = self.client.post(url)
+        self.assertEqual(response.status_code, 201, response.data)
+        app_id = response.data['id']
+
+        # check that updating config rolls a new release
+        url = '/v2/apps/{app_id}/config'.format(**locals())
+        body = {'values': json.dumps({'NEW_URL1': 'http://localhost:8080/'})}
+        response = self.client.post(url, body)
+        self.assertEqual(response.status_code, 201, response.data)
+        self.assertIn('NEW_URL1', response.data['values'])
+
+        # trigger identical release
+        url = '/v2/apps/{app_id}/config'.format(**locals())
+        body = {'values': json.dumps({'NEW_URL1': 'http://localhost:8080/'})}
+        response = self.client.post(url, body)
+        self.assertEqual(response.status_code, 409, response.data)