title: What does the Amazon ELB automatic health check do and what does it expect?
body: <p>Here is the thing:</p>
  
  <ol>
  <li>We've implemented a C++ RESTful API Server, with built-in HTTP parser and no standard HTTP server like apache or anything of the kind</li>
  <li>It has been in use for several months in Amazon structure, using both plain and SSL communications, and no problems have been identified, related to Amazon infra-structure</li>
  <li>We are deploying our first backend using Amazon ELB</li>
  <li>Amazon ELB has a customizable health check system but also as an automatic one, as stated <a href="http://docs.amazonwebservices.com/ElasticLoadBalancing/latest/DeveloperGuide/ts-elb-healthcheck.html">here</a></li>
  <li>We've found no documentation of what data is sent by the health check system</li>
  <li>The backend simple hangs on the socket read instruction and, eventually, the connection is closed</li>
  </ol>
  
  <p>I'm not looking for a solution for the problem since the backend is not based on a standard web server, just if someone knows what kind of message is being sent by the ELB health check system, since we've found no documentation about this, anywhere.</p>
  
  <p>Help is much appreciated. Thank you.</p>