What is CDN exactly?

A Content Delivery Network (CDN) is a network designed to accelerate the delivery of website content to end-users, and ultimately make websites load faster. CDN servers, called edge nodes, are distributed across many regions and used to cache content, thereby reducing the time it takes for users to access the content.

For instance, if your server is located in Tokyo, Japan, but your users are in Australia, the US, and the UK, the time it takes for a user to access your website from the US is approximately 150 milliseconds. In contrast, a user in Japan can access the same content in about 20 milliseconds. To address this disparity, CDN edge nodes are placed in multiple locations, closer to the end-users, to cache the content.

When a user requests content through a URL, the request is routed to the nearest edge node. If the edge node has the requested content in its cache, it is immediately delivered to the user. Otherwise, the edge node retrieves the content from the origin server and caches it for future requests.

One of the indirect benefits of CDN architecture is a reduction in server load. By caching some content, when a user requests the content, the CDN's edge node returns it without requiring the server to handle the request. This results in a reduction in server load, and contributes to an improvement in uptime, which is the percentage of time that the website can be accessed.

In addition, CDN edge servers provide a layer of security by acting as a buffer between the origin server and end-users.