To set Drupal System variables you can use the $settings (on Drupal 8) and $conf (On Drupal 7) array of setting.php file.

Create a custom module (here : example)

For active themes by route you first have to define a service in your $module.services.yml file:

On example.services.yml

Add:

Install Apache following this tutorial

Activate SSL Module

sudo a2enmod ssl

sudo service apache2 force-reload

#Or sudo /etc/init.d/apache2 force-reload

Example:

Get the default cache bin

$cache = \Drupal::cache();

To get a particular cache bin (here 'render'):

$render_cache = \Drupal::cache('render');