CDN

What it means

A CDN, content delivery network, is a network of servers spread around the world that keep copies of a website’s content, such as images, stylesheets and scripts, and serve them to visitors from the nearest location. A visitor in Košice does not wait for a server in another country but gets the files from the closest node.

The main benefit is speed. Shorter distance and optimised delivery improve Core Web Vitals, which affect both visitor satisfaction and search rankings. At the same time the load on the main server falls, so the site copes with sudden traffic spikes.

A modern CDN does more than ship files. It often provides the SSL certificate, protection against DDoS attacks and a web application firewall, and for a static site it can serve the whole website without a traditional server.

How it works in practice

For smaller company websites the CDN is often part of the hosting or is switched on through the domain’s DNS settings. The switch takes hours rather than weeks, but it needs care so that email or domain verification for other services does not break.

For online shops and sites handling sensitive data we also look at data protection. The CDN provider processes visitors’ IP addresses, and if it is based outside the EU, the processing agreement and transfer mechanism need checking. It must also be mentioned in the privacy notice.

CDN costs are an ordinary operating service and a deductible expense. A foreign provider invoices without VAT, and a company that is a VAT payer or registered under Section 7a self-assesses the tax.

What to watch out for

The most common problem after switching a CDN on is visitors seeing an old version of a page because the cache was not purged. When prices or terms of sale change, the cache must be cleared, or an online shop may sell at outdated prices.

A CDN does not guarantee availability if the main server with dynamic content, such as the basket and payment, fails. The promised uptime refers to the CDN network, not the whole application, which should be kept in mind in customer contracts and in recovery planning.