worker protocol only on localhost

templates/buildbot/master.cfg.j2

@@ -10,7 +10,11 @@ c['schedulers'] = []
 c['builders'] = []
 c['services'] = []
 
-c['protocols'] = {'pb': {'port': 9989}}
+c['protocols'] = {
+  'pb': {
+    'port': "tcp:9989:interface=127.0.0.1"
+  }
+}
 
 c['title'] = "buildbot title"
 c['titleURL'] = "https://github.com/covid-videoplattform"