title: What is the recommended way to connect to CloudSQL (or PubSub etc) in a GAE custom runtime
body: <p>I want to deploy a multi-service application on GAE using custom runtimes.</p>
  
  <p>I've everything set, my service expects some environment variable to know when to connect to the database and other services. </p>
  
  <p>But I can't see anywhere in the doc where it explains how to connect to other Google Cloud service from a custom runtime. </p>
  
  <p>If it is explained, thanks for pointing me there. if not, can someone who has been successful on doing that explain to me how he/she achieved it.</p>