HTTPRL

If left blank it will use the same server as the request. If set to -1 it will use the host name instead of an IP address. This controls the output of httprl_build_url_self()
If disabled all background_callback keys will be turned into callback & httprl_queue_background_callback will return NULL and not queue up the request. Note that background callbacks will automatically be disabled if the site is in maintenance mode.
Use httprl to handle all calls to drupal_http_request. Requires 7.22+