When you open a website running on a server on the other side of the world, it loads surprisingly fast. A CDN is largely responsible for this. Let us explain what it is, how it works and why most large websites use it.

What a CDN is

A CDN (Content Delivery Network) is a network of servers spread around the world that keep a copy of a website’s content. When you visit the website, the content is delivered to you not from one distant server, but from the nearest CDN server. This significantly shortens the loading time.

How it works

The original website runs on one server (the origin). The CDN stores a copy of its static content (images, styles, scripts) on its servers in various countries, which are called edge servers (at the edge, close to the user). When you visit the website from Bratislava, you get the content from a nearby European server, not from another continent. This storing is called caching.

How long an edge server keeps the copy is set by the TTL value (time to live). After it expires, or when you change the content, the CDN fetches a fresh version from the origin. Static content (images, fonts) is cached easily, while dynamic content (for example a logged-in account) is mostly pulled straight from the origin. That is why a CDN brings the biggest benefit on sites with lots of static content.

Why a CDN helps

  • Speed. A closer server means faster loading, which you and the search engine appreciate.
  • Resilience. When the website is under a surge of visitors, the CDN spreads the load and relieves the original server.
  • Availability. Even if the original server wavers, the CDN can keep delivering the content.

CDN and security

A CDN often also protects a website from attacks. Since visitors do not talk directly to your server but to the edge network, the CDN hides the origin’s real IP address and can filter out malicious traffic. It can mitigate DDoS attacks, where attackers try to overwhelm the website with a flood of requests. A well-known provider is for example Cloudflare. So a CDN also acts as a shield between the internet and your server. It is worth adding, though, that it is not a full replacement for a firewall, it is one of the layers of protection.

When a CDN is worth it

  • Websites with visitors from several countries or regions.
  • Websites with lots of images and media that the CDN delivers faster.
  • Websites where speed and availability matter, which is also related to SEO.

For a small local website with visitors from the surroundings, a CDN may not be essential, but speed and protection come in handy almost always. Many providers (including Cloudflare) offer a basic version for free, so you can try it at no cost. Deployment is usually simple, in most cases you just point the domain’s DNS records to the CDN, which then takes over delivering the content.

Dealing with the speed or security of your website? Get in touch, we will advise on deploying a CDN and on overall hosting and availability monitoring.