title: Getting 503 Service Unavailable when trying to generate discovery document
body: <p>I'm working with Google Cloud Endpoints, and I'm trying to generate a discovery document to create an iOS client library and so that I can test my endpoints. I tried to do it with this command, as said in the docs:</p>
  
  <pre><code>endpointscfg.py gen_discovery_doc -o . -f rpc appfile.ApiClass
  </code></pre>
  
  <p>With <code>appfile</code> and <code>ApiClass</code> changed to the real names. </p>
  
  <p>When I run this, I get:</p>
  
  <pre><code>urllib2.HTTPError: HTTP Error 503: Service Unavailable
  </code></pre>
  
  <p>Why is generating a discovery document accessing the internet at all? And why am I getting this error? And what can I do to fix it?</p>
  
  <p>P.S. I already checked my code for basic errors like other types in message classes, bad hostnames, etc., but nothing there seems to be the problem.</p>