A Content Delivery Network (CDN) is a network of servers distributed around the world that deliver your site’s static assets — images, CSS, JavaScript, fonts — from a location geographically close to each visitor. If your server is in London and your visitor is in Sydney, a CDN serves the heavy files from a server in Sydney instead of sending them halfway around the planet.
The Geography Problem
Light travels fast, but not instantaneously. A request from Sydney to London covers roughly 17,000 kilometers. At the speed of light through fiber optic cable, that is about 85 milliseconds each way — 170 milliseconds round-trip, just for the signal to travel. Add network congestion, router hops, and server processing time, and a single uncached request can easily take 500-800 milliseconds.
A CDN solves this by placing servers in dozens of cities worldwide. When a visitor requests a file, the CDN serves it from the nearest location — typically within the same city or region. The round-trip time drops from hundreds of milliseconds to single digits.
CDN + Page Caching: Better Together
A CDN and page caching are complementary, not competing. Page caching makes your server fast by serving static HTML instead of generating pages dynamically. A CDN makes your assets fast by serving them from a location close to the visitor. Together, they address both halves of the performance equation: server response time and network latency.
Caching Out includes CDN URL rewriting: you enter your CDN URL (e.g., cdn.yoursite.com), and the plugin rewrites all asset URLs to point to the CDN. It also integrates with Cloudflare, Varnish, and Sucuri to purge their caches automatically when your content changes — so your CDN always serves the latest version of your files.
Do You Need a CDN?
If your audience is local — all within the same country or region as your server — a CDN may not make a dramatic difference. Page caching and file optimization will deliver most of the performance gain. But if your audience is global, or if you serve large markets on multiple continents, a CDN is one of the best investments you can make in site speed.
Further reading: How Page Caching Works for the server-side optimization that pairs with a CDN.