title: Under what circumstances does checkip.amazonaws.com return multiple addresses?
body: <p>I'm trying to understand an issue <a href="https://github.com/nchammas/flintrock/issues/271" rel="noreferrer">reported by a user against one of my open source projects</a>. When they query <code>checkip.amazonaws.com</code> they sometimes get back multiple, comma-delimited IP addresses.</p>
  
  <p>I couldn't find any information about this, so I'm curious:</p>
  
  <ol>
  <li>Is there any proper documentation for this Amazon service?</li>
  <li>Under what circumstances does <code>checkip.amazonaws.com</code> return multiple addresses?</li>
  <li>When it <em>does</em> return multiple addresses, what do they mean? Is there a significance to the order?</li>
  </ol>