What is a CDN?
A Content Delivery Network, a globally distributed cache of edge servers that serves your assets from the location closest to each user.
A CDN places copies of your static assets (images, JS, CSS, video, sometimes HTML) in points of presence (PoPs) around the world. When a user requests one of those assets, the request hits the nearest PoP instead of your origin server, dropping latency from hundreds of milliseconds to single digits.
Modern CDNs do more than caching. They terminate TLS at the edge, enforce WAF rules, run serverless functions on every request (Cloudflare Workers, Fastly Compute, Vercel Edge Functions), bot-detect, and DDoS-absorb. The line between "CDN" and "edge platform" has effectively dissolved.
For websites, the practical impact is that almost every production site sits behind Cloudflare, Fastly, AWS CloudFront, or a managed PaaS that includes one. If you're scraping, the CDN is what fingerprints your client, applies rate limiting, and presents you with the CAPTCHA, not the origin.
In the wild
- Cloudflare caching
/static/main.cssat 300+ PoPs worldwide - Vercel and Netlify serving Next.js static output through their built-in CDN
- Akamai routing video segments through carrier-internal nodes for streaming services