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CDN

A CDN (Content Delivery Network) is a globally distributed network of edge servers that cache your site's static content (HTML, CSS, JS, images, fonts) close to users so each request hits a nearby PoP instead of your origin server.

Updated May 2026 · 4 min read
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Definition

A CDN (Content Delivery Network) is a globally distributed network of edge servers that cache your site's static content (HTML, CSS, JS, images, fonts) close to users so each request hits a nearby PoP instead of your origin server.

What it means

Without a CDN, every visitor's request travels to your origin — sometimes thousands of miles. A user in Tokyo hitting a server in Virginia adds 200ms+ of pure round-trip latency before any rendering can start. A CDN places hundreds of points of presence around the world; the user gets routed to the nearest one (anycast IP), which serves cached content directly. If the cache is cold, the PoP fetches from origin once and caches it for the next visitor. Cloudflare, Fastly, Vercel, AWS CloudFront, and Bunny CDN are the major providers; static-site hosts like Vercel and Netlify include CDN by default.

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Why it matters

CDNs reduce LCP (largest contentful paint) by 200-1500ms for users far from your origin, lower origin bandwidth costs by 80-99% on cached content, and absorb traffic spikes (a CDN doesn't crash if a popular post hits front-page Hacker News). They also add edge security: WAF rules, bot mitigation, DDoS absorption. The downside is cache invalidation complexity — pushing a hotfix means purging the relevant URLs across every PoP.

Frequently asked questions

Do I need a CDN for a small site?

If you're on Vercel, Netlify, Cloudflare Pages, or similar, you already have one — it's the default. For self-hosted small sites, a CDN is still worth it the moment you have international visitors or an embedded image-heavy gallery.

What gets cached?

By default: anything with cache-friendly headers (Cache-Control: public, max-age, immutable). Hashed asset URLs (build-id-based) cache forever; HTML pages typically cache for minutes. The CDN's behavior is driven by the headers your origin sends.

Edge functions vs CDN?

An edge function runs your code at the same PoP that serves your cache. CDNs that support edge compute (Cloudflare Workers, Vercel Edge, Deno Deploy) let you do auth, A/B testing, redirects, even small SSR — all without a round-trip to origin.

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