# Upgrading from 3.0.2 to 3.0.3

Before performing an update you should take your site offline by replacing the index.php file with a static one.

## Step 1: Update your CodeIgniter files

Replace all files and directories in your system/ directory.

Note

If you have any custom developed files in these directories, please make copies of them first.

## Step 2: Make sure your ‘base_url’ config value is not empty

When `$config['base_url']` is not set, CodeIgniter tries to automatically detect what your website’s base URL is. This is done purely for convenience when you are starting development of a new application.

Auto-detection is never reliable and also has security implications, which is why you should always have it manually configured!

One of the changes in CodeIgniter 3.0.3 is how this auto-detection works, and more specifically it now falls back to the server’s IP address instead of the hostname requested by the client. Therefore, if you’ve ever relied on auto-detection, it will change how your website works now.

In case you need to allow e.g. multiple domains, or both http:// and https:// prefixes to be dynamically used depending on the request, remember that application/config/config.php is still a PHP script, in which you can create this logic with a few lines of code. For example:

    $allowed_domains = array('domain1.tld', 'domain2.tld');
    $default_domain  = 'domain1.tld';

    if (in_array($_SERVER['HTTP_HOST'], $allowed_domains, TRUE))
    {
            $domain = $_SERVER['HTTP_HOST'];
    }
    else
    {
            $domain = $default_domain;
    }

    if ( ! empty($_SERVER['HTTPS']))
    {
            $config['base_url'] = 'https://'.$domain;
    }
    else
    {
            $config['base_url'] = 'http://'.$domain;
    }