CDN
Definition & meaning
Definition
A CDN (Content Delivery Network) is a globally distributed network of servers that delivers web content to users from the server geographically closest to them. When a user in Tokyo visits a site hosted in New York, the CDN serves cached content from a server in Tokyo — reducing latency from hundreds of milliseconds to single digits. CDNs cache static assets (images, CSS, JavaScript, fonts), and modern CDNs also cache dynamic content and run serverless functions at the edge. Beyond performance, CDNs provide DDoS protection, SSL termination, image optimization, and traffic analytics. Major CDN providers include Cloudflare (the most widely used), Vercel Edge Network, AWS CloudFront, Fastly, and Akamai. For modern web applications, a CDN is not optional — it is fundamental infrastructure that determines user experience and Core Web Vitals scores.
How It Works
A Content Delivery Network (CDN) is a globally distributed network of proxy servers and data centers designed to serve content from the location nearest to the end user. When a user requests a resource, DNS resolution directs them to the closest CDN edge node (called a Point of Presence or PoP). If that PoP has the content cached, it responds immediately without contacting the origin server — this is a cache hit. On a cache miss, the edge node fetches the resource from the origin, serves it to the user, and caches it for subsequent requests based on cache-control headers. Modern CDNs go beyond simple caching: they terminate TLS connections at the edge (reducing handshake latency), compress assets with Brotli or gzip, optimize images on-the-fly, and run serverless functions at edge locations. CDNs also provide DDoS mitigation by absorbing volumetric attacks across their distributed infrastructure.
Why It Matters
CDNs are no longer optional for production websites — they are infrastructure. Without a CDN, every request travels to a single origin server, meaning users in Tokyo experience 200-400ms of latency hitting a server in Virginia. A CDN reduces that to under 30ms. Google uses page speed as a ranking factor, so CDN adoption directly impacts SEO. Beyond performance, CDNs reduce origin server load by 60-90%, which translates to lower infrastructure costs and better resilience during traffic spikes. They also provide an essential security layer: Cloudflare alone blocks an average of 209 billion cyber threats per day across their network. For any site serving a global audience, a CDN is the single highest-impact infrastructure investment.
Real-World Examples
Cloudflare is the most widely adopted CDN, protecting and accelerating over 20% of all websites. Amazon CloudFront integrates tightly with AWS services. Fastly powers real-time content delivery for companies like GitHub, Stripe, and The New York Times with its Varnish-based edge cloud. Akamai, the original CDN pioneer, handles roughly 30% of global web traffic. Vercel's Edge Network and Netlify's CDN are optimized for JAMstack deployments. For a typical setup, we configure CloudFront in front of an S3 bucket for static assets, set cache-control headers for immutable hashed files, and use Cloudflare as a DNS and security layer with their WAF and bot management rules.
Tools We've Reviewed
Related Terms
Edge Computing
InfrastructureProcessing data near users instead of centralized data centers.
Core Web Vitals
MarketingGoogle's page experience metrics: loading speed (LCP), responsiveness (INP), visual stability (CLS).
SSL/TLS
InfrastructureEncryption protocols securing data between browsers and servers (HTTPS).
Caching
InfrastructureStoring data copies in fast-access locations to avoid repeating expensive operations.