Efficient way to keep Drupal 7 session alive from another web app? Is there a simple PHP file I could create which, when called by an authenticated user, will keep their Drupal session alive? 

I don't want to do an AJAX call to /index.php as this will cause unnecessary overhead. I just need a way to keep the session alive from another app.

Could I use the bootstrap method below, rather than instantiating the whole stack? 

&lt;?php
    define('DRUPAL_ROOT', '/my/local/root');
    include_once(DRUPAL_ROOT . '/includes/bootstrap.inc');
    drupal_bootstrap(DRUPAL_BOOTSTRAP_SESSION);
?&gt;
If you're worried about unnecessary overhead, why not check out the High-performance JavaScript callback handler module. 

It allows you to control what exactly gets loaded during the Drupal bootstrapping process, so that you would only spin up the bare essentials to keep your session alive from another app.

Check out this blog post for a good breakdown of how you implement this module: 

High performance AJAX callbacks with Drupal 7 and the JS module