The Directory Structure

The directory structure of our application will be somewhat as follows:

application/
system/
public_html/
  assets/
  sub-domain-1.example.com/
    assets/
    .htaccess
    index.php
  sub-domain-2.example.com/
    assets/
    .htaccess
    index.php
  ...
  sub-domain-n.example.com/
    assets/
    .htaccess
    index.php

In the above structure:

• application is our application directory
• system contains the CodeIgniter system files, and
• public_html will be the document root of our domain example.com.
• assets directory inside our document root will hold the common assets for our application instances.
• sub-domain-1.example.com through sub-domain-n.example.com will hold our front controllers for each instance of our application. Set the document roots of the sub domains to these directories.
• assets directory inside each of the sub-domain-n.example.com will hold any instance specific assets that we may need (Optional).
• .htaccess inside our each of the sub-domain-n.example will help us remove the index.php from our URLs as well as implement a domain filter.

Now, we’ll walk through the files that need to be modified one-by-one.