Bootstrap for entire application in Yii2?

Question

Yii

I installed the "site settings" module, there is a component there, added it to the bootstrap components in config
For example, I have the item "is the site enabled?"
I need to check setting value and if site is down -> catchAll add to urlManager.
The question is, where and how to make Bootstrap for the whole application in yii ?
So that all components are available in it, and I can do something before transferring control to the controller?
For example check the setting value and "disable" the site.

Answer 1

Config web.php:
MaintenanceMode:
In filtering check for desired conditions and

Yii::$app->catchAll = [self::MAINTENANCE_MODE_ROUTE];

, if needed