Content Delivery Network (CDN)

A content delivery network (CDN) is a geographically distributed overlay of proxy servers — often called edge servers grouped into points of presence (PoPs) — that caches and serves web content from locations close to end users rather than from a single origin data center. The architecture reduces round-trip latency, lowers bandwidth costs by serving cached responses near the user, and shields the origin server from load spikes and abuse. The CDN model was pioneered by Akamai Technologies, founded in 1998 by MIT mathematician Tom Leighton and graduate student Daniel Lewin together with co-founders Jonathan Seelig, Randall Kaplan, Preetish Nijhawan, and Bruce Maggs. The company emerged from research on consistent hashing done in response to a challenge from Tim Berners-Lee about congestion on the early Web, was a finalist in the 1998 MIT $50K competition, and launched its commercial FreeFlow service in 1999. Lewin died aboard American Airlines Flight 11 on September 11, 2001. A typical CDN routes a client to a nearby PoP using DNS-based request routing, Anycast over BGP, or both. If the edge cache has a fresh copy of the requested object it serves the response directly; otherwise it fetches from the origin (sometimes through an intermediate origin shield tier that consolidates misses) and stores the result for subsequent requests. Caching policy is governed by HTTP cache headers and by the operator's own purge and revalidation rules. Early CDNs accelerated only static assets — images, scripts, stylesheets, software downloads, video segments — but modern operators also cache dynamic responses, stream live and on-demand video, and deploy newer transports such as HTTP/2 and HTTP/3 to improve uncached traffic. Major operators today include Akamai, Cloudflare, Fastly, Amazon CloudFront, Google Cloud CDN, and Microsoft Azure Front Door, with Akamai alone reporting roughly 365,000 servers across more than 135 countries. Beyond caching, CDNs have become a core layer of internet infrastructure: they terminate TLS on behalf of customers, provide DDoS Mitigation by absorbing volumetric attacks across their distributed capacity, host Web Application Firewalls and bot management, and run customer code at the edge through Edge Computing platforms such as Cloudflare Workers, Fastly Compute@Edge, and AWS Lambda@Edge. The combination concentrates a growing fraction of global web traffic in a small number of CDN networks, which has made the health of these networks a recurring concern for internet resilience.