CDNs cache content at edge locations close to users, cutting latency and load on the origin. Use for static assets, images, and sometimes API responses. Reduces bandwidth and can improve resilience to traffic spikes.
How a CDN helps
- Lower latency: Users get assets from a nearby edge node instead of your origin. Improves LCP and perceived speed.
- Less origin load: Cached responses do not hit your server. Frees CPU, bandwidth, and reduces risk of overload.
- Bandwidth savings: Many CDNs charge less for edge delivery than you would pay for the same traffic from origin.
What to put on the CDN
- Static assets: JS, CSS, images, fonts. Set long cache TTLs and versioned filenames for cache busting.
- Media: Video and large binaries; offload from origin and often cheaper egress at the edge.
- API: Cacheable GET responses (e.g. public data) can be edge-cached with short TTLs; be careful with personalized or dynamic content.
Best practices
- Cache headers: Use Cache-Control and ETag so the CDN and browsers cache correctly. Invalidate or version when you deploy.
- HTTPS: Serve everything over TLS; most CDNs terminate TLS at the edge and connect to origin over TLS or private link.
- Origin shield: Optional second-tier cache at the CDN to reduce origin requests further.
Summary
CDN = edge cache close to users; lower latency, less origin load, often lower bandwidth cost. Use for static and cacheable content; set cache headers and HTTPS.
