CDN

What it is

Your site lives on one server, somewhere. A visitor three thousand kilometres away pays for that distance twice on every request: once to ask and once to receive. A CDN puts copies of the files on machines near the visitor and answers from there, so the distance disappears.

For a static site that is the whole story: every page is a file, every file can sit at the edge, and the origin server is barely involved after the first request.

Why it matters if you are paying for a website

Mostly for the visitors who are not near your server, which on a Polish business site is more people than you would expect — anyone on a foreign mobile network, anyone abroad, and every crawler that checks your site from wherever it happens to run.

It also absorbs traffic spikes. The day a post does well, the requests hit the edge, not your hosting, and the hosting bill does not notice.

What it does not fix

A slow origin. The first visitor to each page still waits for your server to produce it, and so does the edge every time the cache expires. A CDN in front of a slow WordPress install makes the second visitor’s experience good and leaves the underlying problem exactly where it was.

Anything personalised. A logged-in view, a cart, a page that greets the visitor by name — none of that can be cached and served to everyone, so it goes back to the origin every time.

Slow front-end code. The CDN delivered your three megabytes of JavaScript very quickly. The browser still has to run it.

On this site the question does not really arise: it is static and hosted on Cloudflare Pages, so the CDN is where it lives rather than something bolted in front. That is the arrangement I reach for by default, because the cheapest way to make a CDN effective is to have nothing behind it that needs to run.

What a CDN is not

It is not a backup, and it is not security — although the big ones bundle DDoS protection and a firewall, and those are real features worth having. It is also not a substitute for making the pages smaller: the fastest network in the world still has to carry whatever you put on it.