How a CDN works
Your website still lives on its own server, called the origin. The CDN stores copies of files such as images, stylesheets, scripts and often whole pages in data centres around the world. When someone in Stockholm opens your site, the files come from a nearby CDN server instead of an origin server that may be on another continent. Well-known CDNs include Cloudflare, Amazon CloudFront, Fastly and Akamai.
What is the role of a CDN?
- Speed: faster loading improves the user experience and Core Web Vitals, which are part of Google’s page experience signals.
- Reliability: traffic spikes are spread across many servers, so the site stays up.
- Security: many CDNs filter out attacks and bad bots before they reach your server.
- Less load on your server: the origin handles fewer requests, so it responds faster when it is needed.
A CDN doesn’t replace good hosting or a lean website, but it is one of the simplest ways to speed up a site for visitors in many countries.
CDN example
A shop’s server is in Frankfurt. A customer in Sydney waits several seconds for images to load. The shop starts using a CDN. The first Sydney visitor’s request is passed to Frankfurt, but the images are then stored in a nearby data centre, and the next visitors get them from there in a fraction of the time. The server also handles fewer requests during a sale.
How to set up a CDN
- Choose a provider and check that it has locations near your visitors.
- Point your domain’s DNS to the CDN or install the provider’s plugin.
- Set caching rules: static files for a long time, pages for a shorter time.
- Turn on HTTPS and compression.
- Test speed before and after, and check that logged-in and checkout pages are not cached by mistake.
CDN mistakes
- Caching pages that are personal or change often, such as a cart.
- Forgetting to clear the cache after changes, so visitors see old pages.
- Letting the CDN block Googlebot with security rules.
- Assuming a CDN fixes slow code or very large images.
CDN FAQs
Does a CDN help SEO?
It can, by making pages load faster, which supports page speed and Core Web Vitals. See AMP for an older approach.
Is a CDN only for large sites?
No. Many CDNs have free plans suitable for small sites. See also HTTPS.