CDN (Content Delivery Network)

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CDN (Content Delivery Network)

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Definition

One CDN, or Content Delivery Network, is a distributed network of servers spread across the world, designed to quickly and efficiently deliver static web content such as images, CSS/JS files, fonts, or videos. When a user visits a website using a CDN, content is loaded from the server that is geographically closest to them, reducing load time, improving the user experience, and reducing the load on the origin server.

Why use a CDN?

Using a CDN offers numerous technical and strategic advantages for websites, including:

  • Increased performance : static resources are served more quickly thanks to geographic proximity.
  • Enhanced user experience : smoother charging, especially on mobile phones or in remote areas.
  • Latency reduction : less waiting between the user request and the server response.
  • Main server relief : the CDN absorbs a significant part of the traffic.
  • High availability : In the event of a traffic peak or a local outage, the CDN can redirect to another active node.
  • Enhanced security : protection against DDoS attacks, shared SSL certificates, IP filtering, etc.

How does a CDN work

When a site uses a CDN, here is how a typical request works:

  1. The user requests a resource (e.g. an image).
  2. The browser checks to see if this resource is available in the local cache.
  3. If not, the request is sent to the nearest CDN server (node or PoP — Point of Presence).
  4. This server quickly returns the resource without requesting the primary server, unless the resource is expired or not in the cache.
  5. The result is displayed to the user.

Content typically served by a CDN

Content Type Examples
Static files Minified CSS, JS, HTML
Images JPG, PNG, WebP, SVG
Fonts Google Fonts, Adobe Fonts
Video / audio MP4, HLS, DASH
Heavy media files PDFs, downloadable files

Technical advantages

  • Smart caching : allows frequently requested files to be stored locally.
  • Automatic compression : some CDNs compress files on the fly (ex: Brotli, GZIP).
  • Optimizing images : adaptation according to the browser, resolution, WebP support, etc.
  • Load distribution : requests are distributed between several servers to avoid saturation.

Popular CDN providers

Provider Specificities
Cloudflare CDN + security (WAF, DDoS), free and easy to integrate
Fastly Real-time performance, widely used for media delivery
Amazon CloudFront Integration with AWS, highly customizable
Bunny.net Great price/performance ratio, very fast in Europe
Akamai Extensive global network, used by large enterprises

Integration into a website

A CDN can be integrated in several ways depending on the use case:

  • Through a personalized domain name : ex: cdn.yoursite.com
  • Through a reverse proxy : all traffic goes through the CDN
  • Direct CDN URL integration in the HTML code (e.g. images or hosted scripts)

Some CMS or builders such as Webflow, Shopify or Wordpress offer an automatic integration of a CDN into their offers.

Best practices

  • Verify TTL cached files to avoid outdated content
  • Configure HTTP headers correctly (Cache-Control, ETag...).
  • Analyzing performance with tools like GTmetrix or PageSpeed Insights to ensure proper functioning.
  • Securing the CDN with HTTPS and anti-abuse policies.

In summary

One CDN is a powerful tool for improving the performance, stability and security of a website. By bringing resources closer to the end user, it provides a smooth and fast experience while reducing server load. It is now essential for any site with international traffic or a large volume of media to serve.

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