Moi Verhole

There are three places where Drupal modifies session-handling settings: in the .htaccess file, in the
settings.php file, and in the bootstrap code in the includes/bootstrap.inc file.

Real world example: There can only be one president of a country at a time. The same president has to be brought to action, whenever duty calls. President here is singleton.
Purpose: To have only one instance of this object in the application that will handle all calls.

Key: To create a singleton, make the constructor private, disable cloning, disable extension and create a static variable to house the instance

1. Drupal core, modules, and themes
From an architectural standpoint, we can break up Drupal into three pieces--its core,
modules, and themes.
When we discuss Drupal 8 core, we can interpret it in two ways. A more restrictive
interpretation sees it as a functionality covered in all the code it ships with, without
modules and themes. The more widespread interpretation sees it as the total code base it
ships with (out of the box).

The architectures available for Drupal are those of other LAMP-stack software, and the techniques used
to scale are applicable to Drupal as well. Thus, we’ll concentrate on the Drupal-specific tips and gotchas
for different architectures.