What is a CDN, and do you actually need one?
CDN gets thrown around like everyone already knows what it means. Here is the plain-English version — what it does, how it works, and an honest answer to whether your site needs one.
CDN stands for Content Delivery Network, which is one of those names that technically tells you everything and practically tells you nothing. So let us skip the acronym and talk about the actual problem it solves.
A CDN is a network of servers distributed across many cities that store cached copies of your website and serve them to visitors from the location nearest to them. Instead of every request travelling to your single origin server, most are answered by a nearby edge server in a few milliseconds — which makes pages load faster, takes the load off your server, and keeps the site standing when traffic spikes.
That is the whole idea. Everything else — image optimization, firewalls, compression, waiting rooms — is capability that got added later, because the edge turned out to be a very useful place to put things.
Why does distance make a website slow?
Your website lives on a server somewhere. Say it is in Frankfurt. When someone in Frankfurt visits, the page arrives quickly — the data only has to travel a few kilometres. But when someone in Sydney visits, every request and response has to cross the planet and back, several times, just to load one page. Light is fast, but it is not instant, and all those round trips add up to a site that feels sluggish on the other side of the world.
A single request from Sydney to Frankfurt and back is roughly 300 milliseconds of pure travel time. A page might make dozens of those round trips. That is where "slow" comes from — not your code, just geography.
The round trips add up faster than you think
It is not one trip. Before a browser can even ask for your HTML it has to resolve your DNS, open a TCP connection, and negotiate TLS. On a cold connection that is three round trips before a single byte of your page is requested. At 300 ms each, a Sydney visitor has spent close to a second waiting for permission to start downloading. Then the HTML arrives, references a stylesheet and some fonts, and the whole dance repeats for those.
This is why a CDN helps even when your server is fast. You cannot optimise your way out of the speed of light. You can only shorten the distance.
How does a CDN work?
A CDN is a network of servers — called edge servers, or PoPs (points of presence) — spread across lots of cities. When you put your site behind a CDN, it keeps cached copies of your content on those edge servers. Now the visitor in Sydney loads your site from an edge server in Sydney, not from Frankfurt. Same site, a fraction of the distance.
Cache hit, cache miss
Two things can happen when a request reaches an edge server. If the edge already has a fresh copy of what was asked for, it returns it immediately — a cache hit, typically answered in single-digit milliseconds. If it does not, it fetches the content from your origin, keeps a copy for next time, and passes it on — a cache miss, which costs the full trip to your origin.
The share of requests answered from cache is your cache hit ratio, and it is the number that decides how much good the CDN is doing you. A well-configured static site sits above 95%. A poorly configured one can sit at 40%, forwarding most traffic to the origin and wondering why nothing got faster.
How does the CDN know where to send a visitor?
Two common approaches. GeoDNS answers DNS lookups with a different edge IP depending on where the query appears to come from. Anycast announces the same IP address from every location and lets internet routing deliver the packets to the nearest one. Anycast is generally more robust, because it does not depend on the visitor's DNS resolver being anywhere near the visitor.
What else does a CDN do besides speed?
Speed is the headline, but a CDN quietly does three other useful things:
The offload is the one people underestimate. If your edge answers 95% of requests, your origin sees one request in twenty. A server that was struggling at 500 visitors a minute is suddenly idling, and the hosting plan you were about to upgrade is fine as it is.
Modern CDNs also do work your origin would otherwise do: converting images to WebP or AVIF and resizing them on the fly, compressing text with Brotli, terminating TLS close to the visitor, running a firewall, and holding visitors in a waiting room when a sale gets out of hand.
What a CDN will not fix
Worth being clear about, because a CDN gets blamed for a lot of things it never promised.
- A slow database. If every page needs a fresh query and cannot be cached, the edge is just a relay. Fix the query.
- Heavy JavaScript. The edge can deliver your 2 MB bundle very quickly. The browser still has to parse and execute it.
- Uncacheable pages. A page with a no-store header, or one that varies by cookie for every visitor, will miss every time by design.
- Bad origin uptime, for dynamic content. Cached content survives an origin outage. Anything uncacheable does not.
Do you actually need a CDN?
Honest answer: not everyone does. If your audience is entirely in one city and you get ten visitors a day, a CDN is a solution looking for a problem. But most sites are not like that. Here is a rough guide.
| Your situation | CDN worth it? |
|---|---|
| Visitors in more than one country or region | Yes |
| An online shop where speed affects sales | Definitely |
| Occasional traffic spikes (launches, sales, press) | Yes |
| Lots of images, video or downloads | Yes |
| Compliance rules about where data is served from | Yes — pick your regions |
| A tiny local site with a handful of nearby visitors | Probably not yet |
Rule of thumb: if you have ever thought "the site feels slow for some people" or "I hope it survives launch day", a CDN is the cheapest fix for both.
How do you put a site behind a CDN?
Create a zone pointing at your origin
You give the CDN your current server address. Nothing changes for visitors yet.
Test on the CDN hostname
Every zone gets a hostname you can load in a browser before touching DNS. Click around, check the pages that matter, confirm nothing breaks.
Point your DNS at the CDN
A CNAME (or A record) sends real traffic through the edge. Lower the TTL a day ahead so you can undo it quickly if needed.
Watch your cache hit ratio
This is the number that tells you whether it is working. If it is low, look at what is sending no-cache headers or varying on cookies.
Frequently asked questions
What is a CDN in simple terms?
A CDN, or Content Delivery Network, is a group of servers spread across many cities that hold cached copies of your website. When someone visits, they are served from the server closest to them rather than from your single origin server, which makes the site load faster and takes the traffic load off your own server.
Does a CDN actually make a website faster?
Yes, for two reasons. It cuts the physical distance data has to travel, which removes most of the network round-trip time — often 100 to 300 milliseconds per trip for intercontinental visitors. And it answers most requests from cache in a few milliseconds instead of waiting for your origin server to build the page. The further away your visitors are, the bigger the difference.
Do I need a CDN for a small website?
Not always. If all your visitors are in one city and traffic is low and steady, a CDN adds little. It becomes worth it as soon as you have visitors in other regions, traffic that arrives in bursts, a lot of images or downloads, or a shop where load time affects revenue. Most CDNs have a free tier, so the cost of finding out is close to zero.
What is the difference between a CDN and web hosting?
Web hosting is where your website actually lives — the origin server that runs your code and database. A CDN sits in front of that origin and distributes cached copies of the output. A CDN does not replace hosting; it reduces how often anyone needs to reach it. You still need somewhere for the site to run.
Can a CDN cache dynamic pages?
Yes, with care. Full-page caching of dynamic sites works by caching the pages that are identical for everyone — the catalogue, the blog, the homepage — while bypassing the cache for personal pages such as cart, checkout and account, usually by detecting session cookies. That is how a CDN can put a WordPress or WooCommerce site behind full-page caching without breaking anything.
Does a CDN improve SEO?
Indirectly, and meaningfully. Google measures page experience through Core Web Vitals, and a CDN improves Largest Contentful Paint by serving your main image and HTML from nearby, in modern formats, quickly. It also improves crawl efficiency and reduces the chance of a crawler hitting a timeout. It is not a direct ranking factor by itself, but the things it improves are.
A CDN moves your content closer to your visitors and takes the load off your origin. It makes most sites faster and tougher, and getting started usually takes minutes. If your audience is spread out or your traffic is spiky, it is one of the highest-leverage things you can do — and the number to watch afterwards is your cache hit ratio.
The good news is that trying it does not require a migration or a rewrite. Point a zone at your existing site, and you will see the difference on the very next page load.
See how NordicCDN does this for your site:
Mads has worked in IT — mostly hosting — since he was 16. He took an early stake in a SaaS company and helped grow it through to its acquisition by Visma, has built and run data-center networks, and served as CTO of a Danish data center. He started NordicCDN to make fast, secure infrastructure simple to use.
