What is a CDN?

A CDN (Content Delivery Network) is a network of servers spread around the world that delivers web content to users from the server closest to them.

Normally, your website’s files live on a single server in one location. If that server is in New York and someone visits from Tokyo, every request has to travel all the way across the world and back. That takes time. A CDN solves this by copying your files to dozens or hundreds of servers in different locations. A visitor in Tokyo gets served from a server in Tokyo, and someone in London gets served from one in Europe.

CDNs are especially useful for static assets like images, CSS, JavaScript files, and fonts. These files don’t change often, so they’re easy to cache and distribute. Platforms like Vercel have CDN distribution built in, so your static files are automatically served from a location near your users.

The result is faster load times for everyone, regardless of where they are in the world. CDNs also reduce the load on your origin server and can help absorb traffic spikes, since requests are distributed across many servers instead of all hitting one.

I’ve really only needed a CDN at the application level when I worked at a large consumer tech company serving traffic worldwide. For most projects and MVPs, you can get away without one. But CDNs come up constantly in system design interviews, so it’s one of those things you need to understand well even if you’re not using it day to day.