CDN and Edge Computing — Serve Faster by Getting Closer

The speed of light is your bottleneck#

Your server is in Virginia. Your user is in Tokyo. Light through fiber takes ~70ms one way. With TCP handshake, TLS, and the actual request, that's 200-400ms before any data arrives.

The only way to beat physics: put the content closer to the user.

What a CDN does#

A Content Delivery Network caches your content at edge servers worldwide. When a Tokyo user requests your page, they hit a server in Tokyo — not Virginia.

Static assets (images, CSS, JS, fonts): Cached at edge, served in 5-20ms.

API responses (cacheable): Cached at edge with short TTL, reducing origin load by 80-95%.

Dynamic content: Passes through to origin, but the edge handles TLS termination and connection pooling.

CDN caching strategies#

Cache-Control headers#

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

• public — CDN can cache this
• max-age=31536000 — cache for 1 year
• immutable — don't revalidate even on refresh

For versioned assets (app.a1b2c3.js): Cache forever. The filename changes when content changes.

For HTML pages: Short TTL or stale-while-revalidate:

Cache-Control: public, max-age=60, stale-while-revalidate=300

Serve cached for 60s, then serve stale while fetching fresh in background.

Cache invalidation#

The CDN cached the wrong version. How do you fix it?

• Purge: Delete specific URLs from the cache
• Versioned URLs: /api/v2/data or /app.abc123.js — never invalidate, just deploy new version
• Cache tags: Tag responses, purge by tag (purge all product-123 related)

Edge computing#

CDNs cache static content. Edge computing runs code at the edge.

Edge functions#

Lightweight JavaScript/WASM running at CDN edge locations.

Cloudflare Workers, Vercel Edge Functions, Deno Deploy

export default function handler(request) {
  const country = request.headers.get("cf-ipcountry");
  if (country === "DE") {
    return Response.redirect("/de/");
  }
  return fetch(request);
}

Use cases:

• Geo-routing and personalization
• A/B testing at the edge
• Auth token validation (no round trip to origin)
• API rate limiting
• Bot detection and blocking

Edge vs serverless#

Edge is for lightweight, latency-sensitive work. Serverless is for heavier computation.

The modern stack#

User → Edge (CDN + Workers) → Origin (API) → Database
         ↓
    Cached responses
    Auth validation
    Geo-routing
    A/B tests

The edge handles everything it can. Only requests that need fresh data hit the origin.

Providers#

See CDNs in your architecture#

On Codelit, every architecture with a frontend includes CDN components. Click the CDN node to audit caching strategy, see data flow from origin to edge, and identify what should be cached.

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Optimize your architecture's performance: describe your system on Codelit.io and see where edge caching fits.