Load and merge the configuration files in the index.php.
See the chapter Application Configuration in this wiki.
$yii=dirname(__FILE__).'/../framework/yii.php';
require_once($yii);
...
$configDir = dirname(__FILE__).'/protected/config';
//Merge the config files:
//Settings from the other config files will extend or override the settings from previous (main.php,...)
$config=CMap::mergeArray(
require($configDir.'/main.php'),
require($configDir.'/yiistrap.php'),
require($configDir.'/yiiwheels.php'),
require($configDir.'/mongodb.php'),
.... add more ...
);
Yii::createApplication($config)->run();