Field Guide · concept

Also known as: CDN

A content delivery network (CDN) is a geographically distributed group of servers that cache and serve web content from locations close to users, cutting latency and offloading the origin servers.1

Origin one source Edge PoPregion A Edge PoPregion B Edge PoPregion C user user user fill on miss each user is served from the nearest edge cache, not the distant origin
The origin is copied out to caching nodes — points of presence — spread around the world. A user is routed to the closest one and served over a short hop; the origin is touched only on a cache miss (the dashed links). Most traffic never reaches the origin, so it stays fast and lightly loaded even far away.

Overview

A CDN places caching nodes — points of presence — in many data centers around the world. When a user requests a file, they are routed to the nearest node, which serves a cached copy if it has one or fetches it from the origin and keeps it for the next request. Because most of the traffic (images, video, scripts, static pages) is served from the edge, the origin sees far less load and distant users get content over a short network hop instead of a transcontinental one. CDNs also commonly absorb traffic spikes and blunt denial-of-service attacks.

Where it fits

A CDN is closely related to a reverse proxy and a load balancer — it is essentially a global, caching reverse proxy — and it is a form of edge computing for content. It is a standard tool for scalability in web hosting. A small GopherTrunk dashboard rarely needs one, but a public site distributing decoded archives could front them with a CDN.

Sources

  1. Content delivery network — Wikipedia, on CDN architecture and benefits. ↩

See also