Why is $base_url = http://{$_SERVER['SERVER_NAME']} in settings.php? Will this cause any problems?
If the site is served by a single application server and that name will never change, then this isn't wrong, but not the way I would do it.

If you want to use SERVER_NAME and avoid issues if it's not initialized:

$base_url = isset($_SERVER['SERVER_NAME']) ? $_SERVER['SERVER_NAME'] : '';


Or, instead of empty quotes, specify the server name if it doesn't change.