So, how do you use CDN in your application? In best practice, if your application has high traffic, creating different subdomains at your CDN for each content type is the best. For example, a separate domain for CSS and JavaScript files, a subdomain for images, and another separate subdomain for audio/videos files can be created. This way, the browser will send parallel requests for each content type. Let's say, we have the following URLs for each content type:

Now, most open source applications provide settings at their admin control panel to set up CDN URLs, but in case you happened to use an open source framework or a custom-build application, you can define your own setting for CDN by placing the previous URLs either in the database or in a configuration file loaded globally.

For our example, we will place the preceding URLs in a config file and create three constants for them, as follows:

Constant('CSS_JS_URL', 'http://css-js.yourcdn.com/');
Constant('IMAGES_URL', 'http://images.yourcdn.com/');
Constant('MEDiA_URL', 'http://css-js.yourcdn.com/');

If we need to load a CSS file, it can be loaded as follows:

<script type="text/javascript" src="<?php echo CSS_JS_URL ?>js/file.js"></script>

For a JavaScript file, it can be loaded as follows:

<link rel="stylesheet" type="text/css" href="<?php echo CSS_JS_URL ?>css/file.css" />

If we load images, we can use the previous way in the src attribute of the img tag, as follows:

<img src="<?php echo IMAGES_URL ?>images/image.png" />

In the preceding examples, if we don't need to use CDN or want to change the CDN URLs, it will be easy to change in just one place.

Most famous JavaScript libraries and templating engines host their static resources on their own personal CDN. Google hosts query libraries, fonts, and other JavaScript libraries on its own CDN, which can be used directly in applications.

Sometimes, we may not want to use CDN or be able to afford them. For this, we can use a technique called domain sharing. Using domain sharding, we can create subdomains or point out other domains to our resources' directories on the same server and application. The technique is the same as discussed earlier; the only difference is that we direct other domains or subdomains to our media, CSS, JavaScript, and image directories ourselves.

This may seem be fine, but it won't provide us with CDN's best performance. This is because CDN decides the geographical availability of content depending on the customer's location, extensive caching, and files optimization on the fly.