CDN (content delivery network)
A worldwide network of caching servers that keeps copies of your files near your visitors, so downloads come from the next city.
See it
What it is
A CDN is a fleet of caching servers (points of presence, or PoPs) spread across the world. The first visitor in Singapore pulls your logo from your real server; every visitor after that gets the copy already sitting in Singapore. You cut the round trip from 300ms to 20ms without changing a line of application code.
Reach for one the moment you serve static assets to people outside your server's region: images, video, JS, CSS, fonts, downloads. Modern CDNs (Cloudflare, Fastly, Akamai, CloudFront, plus whatever your host bundles) also do TLS termination, compression, image resizing, and running code at the edge, so the 'file cache' framing undersells them.
Gotcha: a CDN only helps for things it is allowed to cache. A 'no-store' response, or a cache key that varies per user, goes to your origin server every time, and you get the extra hop with none of the speed. Cookies are fuzzier than the folklore says: a request cookie only bypasses the cache when your cache policy or your cache key makes it, and what a CDN does with a 'Set-Cookie' on the way back is provider-specific, from refusing to store the response to stripping the header. Mark anything user-specific 'private' or 'no-store' yourself instead of trusting a default to notice. Then check your hit ratio before you assume the CDN is working.
Ask AI for it
Put this site behind a CDN. Point the domain at the CDN instead of the origin, cache all static assets at the edge, and set Cache-Control: public, max-age=31536000, immutable on content-hashed JS, CSS, and font files while keeping HTML short-lived with stale-while-revalidate. Turn on Brotli compression and HTTP/3, and show me the response headers that prove a request was served from a nearby edge location rather than the origin.