Glossary / CDN

What is a CDN (Content Delivery Network)

A CDN (Content Delivery Network) is a worldwide network of servers that store copies of your site's files and serve them to each visitor from the nearest location. Instead of pulling images and scripts from one distant server, the browser grabs them nearby. That speeds up loading and takes load off your main hosting.

When a visitor opens the site, the CDN detects their location and serves static files (images, CSS, JS, video) from the closest node. Those files are cached on the nodes, so your origin server no longer has to hand them out and gets a break.

A CDN helps most for sites with an audience across countries or with many heavy files. Beyond speed, it adds resilience to traffic spikes and basic DDoS protection, because an attack spreads across nodes. The best known are Cloudflare, Fastly, Amazon CloudFront, and Google Cloud CDN.

A CDN does not replace hosting: dynamic pages are still built by your server. It only speeds up delivery of static files and cached responses.

Example

cf-cache-status: HIT

Common mistakes

• Thinking a CDN replaces hosting, when it only caches and serves files while the site itself lives on your server.
• Believing every site needs a CDN, when a small site with a local audience gains little.
• Forgetting SSL: the wrong mode (Flexible instead of Full) on Cloudflare causes endless redirects.
• Not purging the CDN cache after an update and seeing the old version.

Related terms

• TTFB What is TTFB (Time To First Byte)
• HTTP/2 What is HTTP/2
• HTTP/3 What is HTTP/3
• gzip / Brotli What is gzip and Brotli compression
• DNSBL What is a DNSBL (blacklist)