多台服务器下共享session cookie

ini_set('session.cookie_path', '/');
ini_set('session.cookie_domain', '.test.com');
ini_set('session.cookie_lifetime', '1800');
if($_SERVER['HTTP_HOST']=='test.com'){
header('HTTP/1.1 301 Moved Permanently');
header("Location: http://www.test.com/");
exit;
}