A Content Delivery Network (CDN) stores copies of your static files — images, CSS, JavaScript, videos — on servers around the world. When someone in Tokyo requests your logo, they get it from a nearby edge location instead of waiting for a round trip to your origin server in Virginia. Pages feel snappier; your main server handles less traffic.
Cloudflare, Amazon CloudFront, Google Cloud CDN, and Azure CDN all do variations of this. You point your domain or asset URLs at the CDN, configure cache rules, and the CDN fetches from your origin when it does not have a fresh copy. Repeat visitors and popular files hit the edge cache and load almost instantly.
Caching is not "set and forget." You choose how long files stay cached (TTL), what to purge when you deploy, and whether HTML pages cache at all. Aggressive caching speeds things up but can show old content after an update. Most teams cache images and scripts heavily, cache HTML lightly or not at all, and purge the CDN as part of their deploy script.
CDNs also help with traffic spikes. A product launch or viral post can overwhelm a single origin server. The CDN absorbs most read requests. Pair that with a load balancer and autoscaling on your app tier and you survive busy days without rewriting the whole architecture the night before launch.
Security benefits come along for the ride. Many CDNs offer DDoS protection, Web Application Firewalls (WAF), and free TLS certificates. That is not a replacement for secure code, but it filters a lot of junk before it reaches you. For public websites and APIs, putting a CDN in front is one of the highest-impact, lowest-effort upgrades.
When should you add a CDN? If you have users in multiple countries, serve large images or videos, or see slow page scores in tools like Lighthouse — probably now. Setup takes an afternoon for a static site and a bit longer for dynamic apps. Measure before and after; the speed gain is usually obvious on the first test from a distant location.