A content delivery network (CDN) is a network of servers spread across many locations that keep copies of your website’s files, and sometimes whole pages, and serve each visitor from the one nearest to them. Instead of every request travelling to your own hosting server, most are answered close to the visitor, so pages arrive faster and your server does less work.
How a CDN works
Once a CDN is set up, your domain’s DNS sends visitors to the CDN rather than straight to your host. Each CDN location, often called an edge server or point of presence, checks whether it already holds a fresh copy of the file requested. If it does, it sends it immediately. If not, it fetches the file from your server, known as the origin, passes it on and keeps a copy for the next visitor.
By default most CDNs store static files: images, stylesheets, scripts and fonts. Many can also store complete HTML pages, which gives the biggest speed gain but needs care, because pages with personal content must never be shared between visitors. The same caching rules about expiry and purging apply at the edge.
Modern CDNs do much more than store files. Common extras include automatic compression and image resizing, newer connection protocols, a web application firewall, protection against floods of malicious traffic and controls over which bots may visit. Well-known providers include Cloudflare, Fastly, Amazon CloudFront and Bunny.net, and hosted platforms such as Shopify and Squarespace include a CDN as standard.
Why it matters
For UK visitors, the location point is simple: the major CDNs run edge servers in London and often other UK cities. If your host is abroad, a CDN can remove most of the delay that distance adds. If your host is already in the UK, the speed gain for UK visitors is smaller, and the larger benefits are reduced load on your server, steadier performance during traffic spikes and protection from attacks.
There is also a data protection side. A CDN handles every visitor’s IP address, which counts as personal data under UK GDPR, so the CDN provider acts as your data processor. You need a data processing agreement with it, a mention in your privacy notice and, if data leaves the UK, a valid basis for the transfer. Most large providers publish standard terms, but you still need to accept and keep them.
Common mistakes
- Caching account, basket or checkout pages at the edge, so one customer can see another’s details.
- Not purging the CDN after edits, leaving old prices or content visible for hours.
- Leaving the origin server open to direct traffic, so attackers bypass the CDN’s firewall altogether.
- Switching on aggressive bot blocking that also stops search engine crawlers. Some CDNs now offer or default to blocking AI crawlers, at the time of writing (October 2026), which can keep your content out of AI search answers if you want to appear there.
- Expecting a CDN to fix a slow server. Pages that cannot be cached still wait for the origin.
How to act on it
First, check whether you already use one: response headers such as cf-ray, x-cache or via in your browser’s developer tools give it away. If you do, find out who controls the account and what it is set to cache.
Then confirm the essentials: personal pages excluded, purging tied to publishing, the origin locked down and bot settings reviewed so Googlebot and any AI crawlers you welcome can reach the site. File the provider’s data processing terms with your other UK GDPR records.
Finally, measure speed before and after any change, from a logged-out browser. Setting up and checking a CDN properly is part of the technical SEO service I run, because a misconfigured one can hide content from search engines as easily as it speeds pages up.