fix(tags): improve the error message when the combination of tags match no node labels

Fixes #486

Author: helgi

rootfs/api/models/config.py

@@ -67,10 +67,15 @@ def save(self, **kwargs):
             nodes = self._scheduler._get_nodes(labels=self.tags).json()
             if not nodes['items']:
                 labels = ['{}={}'.format(key, value) for key, value in self.tags.items()]
-                raise EnvironmentError(
-                    'These tags do not match labels on kubernetes nodes: {}'.format(
-                        ', '.join(labels)
-                    )
-                )
+                message = 'No nodes matched the provided labels: {}'.format(', '.join(labels))
+
+                # Find out if there are any other tags around
+                old_tags = getattr(previous_config, 'tags')
+                if old_tags:
+                    old = ['{}={}'.format(key, value) for key, value in old_tags.items()]
+                    new = set(labels) - set(old)
+                    message += ' - Addition of {} is the cause'.format(', '.join(new))
+
+                raise EnvironmentError(message)
 
         return super(Config, self).save(**kwargs)

rootfs/api/tests/test_config.py

@@ -503,6 +503,14 @@ def test_tags(self):
         response = self.client.post(url, json.dumps(body), content_type='application/json',
                                     HTTP_AUTHORIZATION='token {}'.format(self.token))
         self.assertEqual(response.status_code, 201)
+        body = {'tags': json.dumps({'host.the-name.com/does.no.exist': 'valid'})}
+        response = self.client.post(url, json.dumps(body), content_type='application/json',
+                                    HTTP_AUTHORIZATION='token {}'.format(self.token))
+        self.assertContains(
+            response,
+            'Addition of host.the-name.com/does.no.exist=valid is the cause',
+            status_code=400
+        )
         # set invalid values
         body = {'tags': json.dumps({'valid': 'in\nvalid'})}
         response = self.client.post(url, json.dumps(body), content_type='application/json',