What Is a CDN? A Beginner's Guide to Content Delivery Networks
The Problem a CDN Solves
Every website lives on an origin server somewhere. If that server is in Virginia and you open the site from Mumbai, your request has to cross thousands of miles of fiber, hop through dozens of routers, and wait for the origin to build the response before the bytes start coming back. That round trip costs time — often more than the actual work of generating the page.
A content delivery network fixes this by putting copies of your content closer to users. Instead of one origin, you get edge servers distributed across many cities and continents. When a user requests a large image, a video segment, or a mostly static HTML page, the nearest edge server can serve it directly without bothering the origin at all. The result is that the page feels instant, the origin stays quiet enough to handle real work, and the cost of moving bytes drops.
How Edge Caching Actually Works
The mechanism is caching, not magic. When an edge server does not have a copy of a file, it asks the origin for it once, stores the result, and serves subsequent requests from cache until the cached version expires or is invalidated. Cache headers on the origin's responses tell edge servers how long to keep each asset.
CDNs also sit between users and the origin in another useful sense: they absorb traffic spikes and blunt many attacks. A sudden flood of requests for a cached resource is handled at the edge and never reaches the origin. This makes CDNs a quiet backbone of the modern web, especially for any site that serves media, runs ads, or markets to a global audience.
The Edge Review writes beginner-focused explainers on infrastructure topics. Specific CDN products and caching behaviors vary by vendor; check your provider's documentation before configuring production rules.