Make haproxy instanciation fail when backend-dict is empty.

slapos/recipe/haproxy/__init__.py

@@ -76,6 +76,10 @@ class Recipe(GenericBaseRecipe):
       backend_dict = {
         self.options['name']: (self.options['port'], backend_list),
       }
+    if not backend_dict:
+      # Fail installation if backend_dict is empty, otherwise partition may be
+      # advertised as available although it provides no service.
+      raise Exception('backend-dict is empty')
 
     server_snippet_filename = self.getTemplateFilename(
       'haproxy-server-snippet.cfg.in')