A plugin to activate/deactivate maintenance mode for CakePHP apps.
There's a view file if you need to change the message or appearance.

Load the component in you app_controller.php

var $components = array('Maintenance.Maintenance');

This will force your application into maintenance mode, so each request will be redirected to /maintenance.

How if you want the URL like / ? That's easy ... look at maintenance/config/settings.php and read the example or just copy require_once block into APP/config/routes.php and put on top of other URL patterns.

require_once App::pluginPath('maintenance').'/config/routes.php';