CDN & Edge Computing Guides

A CDN is the most-used networking feature on the public internet that most people never think about — every Netflix stream, every Instagram image, every npm download, every game patch comes through one. Modern CDNs also run application code at the edge, do TLS termination, mitigate DDoS, and act as the security gateway for entire websites. These guides explain how the major pieces work in plain English, with specific cache-header semantics, anycast routing details, and the operational trade-offs that determine whether a CDN deployment helps or hurts your application.

Where to start

If you are new to CDNs, start with how a CDN works — points of presence, anycast routing, and cache hit logic. Everything else builds on those fundamentals.

If you are debugging a specific cache problem, jump to cache-control headers — most CDN behavior is controlled by HTTP headers, and most bugs are misconfigured headers.

If you are building an application that runs code at the edge, see edge functions explained for the model differences between Cloudflare Workers, Lambda@Edge, and Vercel Edge.

CDN fundamentals

How content moves from origin to user via the CDN's distributed network.

Fundamentals

How a CDN Works

Points of presence, edge servers, cache hits and misses, and origin shielding.

Cache-Control Headers Explained

Cache-Control, Vary, ETag, Surrogate-Control — the headers that drive CDN behavior.

Anycast vs GeoDNS

How CDNs decide which POP serves which user — the routing layer underneath everything.

Tiered Caching Explained

Regional shields and the cache hierarchy that protects origin from cold-miss bursts.

Cache Mechanics

Cache Key and Vary Header

How edges decide two requests are the same content — and how Vary changes that.

Stale-While-Revalidate

Serve stale content instantly while a fresh copy fetches in the background.

ETag and Conditional Requests

Validators, If-None-Match, and 304 Not Modified — cheap revalidation explained.

Cache Hit Ratio

Request hit rate vs byte hit rate, and what moves the number.

Media at the Edge

Image Optimization at the Edge

Format negotiation, resize, AVIF/WebP/JPEG, and responsive image patterns.

Video Streaming via CDN

HLS, DASH, CMAF, segment caching, and adaptive bitrate.

Edge Computing

CDN vs Edge Computing

Content delivery vs compute at the edge — overlapping vocabulary, different products.

Edge Functions Explained

Cloudflare Workers, Lambda@Edge, Vercel Edge, Deno Deploy — runtime models and trade-offs.

Operations & Security

CDN Purge and Invalidation

Cache busting strategies — tag-based, URL, soft-purge, and the propagation gotchas.

WAF, DDoS, and Bot Mitigation

The security layer on top of every modern CDN — what they actually protect against.

CDN Logs and Observability

Edge access logs, cache-status headers, and diagnostic patterns.