
<h2>What is a Dangling Server</h2>

Sometimes we need to make sure on one single web page, two AJAX requests hit
servers that are running with the same version of PHP code. This isn't always
the case during push time. Dangling server is trying to solve this problem by
running old instance of server on a different port for longer time before
shutting down. This way, on new server, if a page detects that the page needs
to be served from old version, it can simply call:

  if (dangling_server_proxy_old_request()) {
    exit;
  }
  // otherwise continue executing the page with new version

What dangling_server_proxy_old_request() will do is to send an HTTP request to
the local dangling server with URL, headers and POST data of current request,
and update current response's headers and output buffer with what it gets. It
will return false, if it failed to contact the dangling server that may have
shut down eventually.

Similarly, an old server can call dangling_server_proxy_new_request(), if it
knows which servers will surely get new version of the software first:

  if (dangling_server_proxy_new_request($host)) {
    exit;
  }
  // otherwise, do something about it