title: Should a 502 HTTP status code be used if a proxy receives no response at all?
body: <p>According to the RFC:</p>
  
  <blockquote>
    <p><strong>10.5.3 502 Bad Gateway</strong><br/>
    The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request.</p>
  </blockquote>
  
  <p>Can <em>invalid response</em> also mean no response at all (e.g. connection refused)?</p>