# CDN *Content Delivery Network* A CDN is a network of servers around the world that keep copies of your site and answer visitors from whichever one is nearest. It removes the distance between the visitor and the origin server — and only that. **Canonical:** https://spoko.space/glossary/cdn/ **Language:** en **Category:** Performance **Also known as:** content delivery network, edge network **Published:** 2026-09-22 **Glossary:** https://spoko.space/glossary/ --- ## What it is {#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 {#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 {#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 {#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. ## Related terms {#related-terms} - [LCP](https://spoko.space/glossary/lcp/): LCP measures when the largest element in the viewport finishes rendering — usually the hero image or the headline. Google calls 2.5 seconds or less good, measured on real visits at the 75th percentile. — Markdown: https://spoko.space/glossary/lcp.md - [SSG](https://spoko.space/glossary/ssg/): Static site generation builds every page into a finished HTML file before anyone visits, so a request is answered by a file server instead of by code, a database query and a template rendered on the spot. — Markdown: https://spoko.space/glossary/ssg.md - [Core Web Vitals](https://spoko.space/glossary/core-web-vitals/): Core Web Vitals are the three metrics Google collects from real Chrome visits: LCP for loading, INP for responsiveness and CLS for visual stability. A URL passes when 75% of its visits are inside the good threshold. — Markdown: https://spoko.space/glossary/core-web-vitals.md - [CLS](https://spoko.space/glossary/cls/): CLS scores how much a page jumps around while it loads, on a unitless scale where 0.1 or less is good. Every element that moves without the visitor causing it adds to the score, weighted by how far it moved and how much of the screen it took. — Markdown: https://spoko.space/glossary/cls.md ## Where I write about this {#related-posts} - [Parts & Accessories Catalog](https://spoko.space/vw-polo-6r-parts-catalog/) — Markdown: https://spoko.space/vw-polo-6r-parts-catalog.md Headless CMS parts catalog for VW Polo 6R. Astro SSG, Vue 3, Laravel API, Filament admin, AI descriptions, DeepL translations and Cloudflare R2 image pipeline. - [GotowySMS: A Platform for Ready-Made SMS Texts](https://spoko.space/gotowysms/) — Markdown: https://spoko.space/gotowysms.md Static site with ready-to-use wish texts and SMS templates, powered by a custom CMS on Laravel 13 + FilamentPHP. Architecture built to withstand seasonal traffic spikes. - [Japanese SEO Spam on WordPress — How to Spot and Remove It](https://spoko.space/blog/japanese-seo-spam-wordpress/) — Markdown: https://spoko.space/blog/japanese-seo-spam-wordpress.md Your site looks normal, while Google shows hundreds of Japanese shop pages that never existed. How to spot the keyword hack and clean it out for good. - [Web application vs website — what is the difference?](https://spoko.space/blog/web-application-vs-website/) — Markdown: https://spoko.space/blog/web-application-vs-website.md A website presents content. A web application lets the user do something. See the differences, when to choose which, and how much each costs. ## See also {#see-also} - [WordPress → Astro migration](https://spoko.space/wordpress-to-astro/) ## Sources {#sources} - [Content delivery networks (CDNs)](https://web.dev/articles/content-delivery-networks) — What a CDN caches, what it cannot, and how the cache is invalidated.