The database.php

The database configuration of each instance is kept in application/config/database.php in a separate db_group. Since we have assigned the db_group in our front-controller, we just need to set the same in our database.php.

Here is our database.php:

$active_group = config_item('db_group'); 
$query_builder = TRUE; 

$db['subdomain-1'] = array(
    'dsn'	   => '',
    'hostname' => 'localhost',
    'username' => 'user_1',
    'password' => 'pass_1',
    'database' => 'db_1',
    'dbdriver' => 'mysqli',
    // ...
    'save_queries' => FALSE
); 

$db['subdomain-2'] = array( 
    'dsn'	   => '', 
    'hostname' => 'localhost', 
    'username' => 'user_2', 
    'password' => 'pass_2', 
    'database' => 'db_2', 
    'dbdriver' => 'mysqli', 
    // ...
    'save_queries' => FALSE
);

// ... so on for every instance