CDN — How It Works

CDN distributes content via edge servers around the world. Lower latency, higher availability.

Principle¶

Edge servers cache content close to users. Tokyo -> edge in Tokyo instead of origin in Prague.

What to Cache¶

• Static files (CSS, JS, images) — long TTL
• HTML — short TTL / stale-while-revalidate
• API — read-only, public only
• Video/audio — ideal use case

Cache-Control¶

Static assets¶

Cache-Control: public, max-age=31536000, immutable

HTML¶

Cache-Control: public, max-age=300, stale-while-revalidate=86400

Never¶

Cache-Control: no-store

Providers¶

• Cloudflare — free, DDoS, Workers
• CloudFront — AWS, Lambda@Edge
• Fastly — real-time purging
• Vercel/Netlify — JAMstack

CDN = Speed + Availability¶

A standard for any public-facing website.