diff --git a/heat/engine/service_software_config.py b/heat/engine/service_software_config.py
index aa203ae123..82cb0f0af6 100644
--- a/heat/engine/service_software_config.py
+++ b/heat/engine/service_software_config.py
@@ -111,51 +111,47 @@ class SoftwareConfigService(object):
 
         metadata_put_url = None
         metadata_queue_id = None
-        metadata_headers = None
         for rd in rs.data:
             if rd.key == 'metadata_put_url':
                 metadata_put_url = rd.value
             if rd.key == 'metadata_queue_id':
                 metadata_queue_id = rd.value
-        if metadata_put_url:
-            data = requests.head(metadata_put_url)
-            etag = data.headers.get('etag')
-            if etag:
-                metadata_headers = {'if-match': etag}
-            else:
-                LOG.warning("Couldn't find existing Swift metadata "
-                            "for server %s", server_id)
 
+        action = _('deployments of server %s') % server_id
+        atomic_key = rs.atomic_key
         rows_updated = db_api.resource_update(
-            cnxt, rs.id, {'rsrc_metadata': md}, rs.atomic_key)
+            cnxt, rs.id, {'rsrc_metadata': md}, atomic_key)
         if not rows_updated:
-            LOG.debug('Conflict on deployment metadata update for '
-                      'server %s; retrying', server_id)
-            action = _('deployments of server %s') % server_id
+            LOG.debug('Retrying server %s deployment metadata update',
+                      server_id)
             raise exception.ConcurrentTransaction(action=action)
-        LOG.debug('Updated deployment metadata for server %s', server_id)
+
+        LOG.debug('Updated server %s deployment metadata', server_id)
 
         if metadata_put_url:
             json_md = jsonutils.dumps(md)
-            resp = requests.put(metadata_put_url, json_md,
-                                headers=metadata_headers)
-            if resp.status_code == requests.codes.precondition_failed:
-                LOG.debug('Conflict on Swift deployment update for '
-                          'server %s; retrying', server_id)
-                action = _('deployments of server %s') % server_id
-                raise exception.ConcurrentTransaction(action=action)
-            else:
-                try:
-                    resp.raise_for_status()
-                except requests.HTTPError as exc:
-                    LOG.error('Failed to deliver deployment data to '
-                              'server %s: %s', server_id, exc)
+            resp = requests.put(metadata_put_url, json_md)
+            try:
+                resp.raise_for_status()
+            except requests.HTTPError as exc:
+                LOG.error('Failed to deliver deployment data to '
+                          'server %s: %s', server_id, exc)
         if metadata_queue_id:
             project = stack_user_project_id
             queue = self._get_zaqar_queue(cnxt, rs, project, metadata_queue_id)
             zaqar_plugin = cnxt.clients.client_plugin('zaqar')
             queue.post({'body': md, 'ttl': zaqar_plugin.DEFAULT_TTL})
 
+        # Bump the atomic key again to serialise updates to the data sent to
+        # the server via Swift.
+        if metadata_put_url is not None:
+            rows_updated = db_api.resource_update(cnxt, rs.id, {},
+                                                  atomic_key + 1)
+            if not rows_updated:
+                LOG.debug('Concurrent update to server %s deployments data '
+                          'detected - retrying.', server_id)
+                raise exception.ConcurrentTransaction(action=action)
+
     def _refresh_swift_software_deployment(self, cnxt, sd, deploy_signal_id):
         container, object_name = urlparse.urlparse(
             deploy_signal_id).path.split('/')[-2:]
diff --git a/heat/tests/engine/service/test_software_config.py b/heat/tests/engine/service/test_software_config.py
index 15079dcd45..038d7a04f6 100644
--- a/heat/tests/engine/service/test_software_config.py
+++ b/heat/tests/engine/service/test_software_config.py
@@ -693,9 +693,8 @@ class SoftwareConfigServiceTest(common.HeatTestCase):
     @mock.patch.object(db_api, 'resource_update')
     @mock.patch.object(db_api, 'resource_get_by_physical_resource_id')
     @mock.patch.object(service_software_config.requests, 'put')
-    @mock.patch.object(service_software_config.requests, 'head')
     def test_push_metadata_software_deployments_temp_url(
-            self, head, put, res_get, res_upd, md_sd):
+            self, put, res_get, res_upd, md_sd):
         rs = mock.Mock()
         rs.rsrc_metadata = {'original': 'metadata'}
         rs.id = '1234'
@@ -707,14 +706,6 @@ class SoftwareConfigServiceTest(common.HeatTestCase):
         res_get.return_value = rs
         res_upd.return_value = 1
 
-        head_response = mock.Mock()
-        head_response.headers = {'etag': '1234'}
-        head_response.status_code = 200
-        head.return_value = head_response
-
-        put_response = mock.Mock()
-        put_response.status_code = 201
-
         deployments = {'deploy': 'this'}
         md_sd.return_value = deployments
 
@@ -725,12 +716,15 @@ class SoftwareConfigServiceTest(common.HeatTestCase):
         with mock.patch.object(self.ctx.session, 'refresh'):
             self.engine.software_config._push_metadata_software_deployments(
                 self.ctx, '1234', None)
-        res_upd.assert_called_once_with(
-            self.ctx, '1234', {'rsrc_metadata': result_metadata}, 1)
+        res_upd.has_calls(
+            mock.call(self.ctx, '1234',
+                      {'rsrc_metadata': result_metadata}, 1),
+            mock.call(self.ctx, '1234',
+                      {'rsrc_metadata': result_metadata}, 2),
+        )
 
         put.assert_called_once_with(
-            'http://192.168.2.2/foo/bar', json.dumps(result_metadata),
-            headers={'if-match': '1234'})
+            'http://192.168.2.2/foo/bar', json.dumps(result_metadata))
 
     @mock.patch.object(service_software_config.SoftwareConfigService,
                        'metadata_software_deployments')