Global Scale with CDNs

If your server is in New York, a user in Tokyo has to wait 200ms just for the signal to travel. CDNs solve this by placing "Edge Servers" in every major city on Earth.

1. Edge Caching

Static assets (Images, CSS, JS) are cached at the edge. When a Tokyo user requests logo.png, they get it from a server in Tokyo, reducing latency from 200ms to 5ms.

2. Edge Computing (Cloudflare Workers / Lambda@Edge)

Modern CDNs allow you to run Code at the edge. You can handle authentication, A/B testing, or Geo-targeting logic right at the user's location, without ever hitting your central origin server.

4. Interview Mastery

Q: "What is 'Push' vs 'Pull' CDN?"

Architect Answer: "**Pull CDN** (Most common) waits for a user to request a file, then grabs it from your server and caches it. **Push CDN** is when your build system manually uploads all assets to the CDN ahead of time. Push is better for giant files (like high-res videos) that you want to be globally available the second they are published."