Using non-relative URL's during early development can alleviate a lot of growing pains. This may seem counter-intuitive at first, but hear me out. We all learned long ago to stop hard-coding the domain name into the href attribute of an anchor tag. Instead, we used relative URL's such as '/index.php' to make our code much more portable. However, relative URL's become a pain point when trying to scale your website. Let's review some common scenarios that can be averted with some proper planning.

Common scenario's:

1. The time comes for a CDN and all images need to be served up with a URL like cdn.example.com.
2. The use of SSL is very common for authentication and other sensitive user information. The problem is that SSL is much slower than a normal http request. Traffic needs to be segregated by changing the SSL URL's from https://www.example.com to https://secure.example.com.

The solution to these problems is quite trivial: simply prepend a domain to a relative URL. Consider the following config file:

[development]
site.cdn = "http://dev.example.com"
site.ssl = "https://dev.example.com"

[production]
site.cdn = "http://cdn.example.com"
site.ssl = "https://secure.example.com"

This configuration uses special URL values for a production environment, but uses the standard development server URL so the developers can still develop. A simple addition to the php bootstrap file can set up defines to use in html templates.

site->cdn);
define('SSL', $config->site->ssl);

And then in a .phtml file you can simply do the following:

Login

Consider prepending the domain for all URL's in your application, not just those types listed above. There are plenty of scenario's that may require AJAX calls or even normal GET/POST request to use different domains.