How to run Slim on Google App Engine/Cloud Platform

Not only do you need a default script handler that points to your index.php file, but you will also need to manually populate the PATH_INFO attribute of Slim's Environment object. Additionally, App Engine doesn't set $_SERVER['SERVER_PORT'], which Slim doesn't use directly, but attempts to set to its Environment object. If you don't manually set SERVER_PORT on the $_SERVER object, GAE will fire a warning every time Slim loads up.