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Content delivery network

A content delivery network, or CDN, is a network of servers in different locations that delivers website content from locations closer to visitors. A CDN can store temporary copies of suitable files, such as images or style sheets, so each request does not have to travel to the website's original server.

How does a CDN deliver a page?

When a browser requests a file, DNS and the CDN's routing system direct the request to a nearby or otherwise suitable CDN server. If that server has a usable cached copy, it can return the copy. If the content is not cached or must be current, the CDN can request it from the website's origin server, then deliver it to the visitor. Content generated for a particular request may need the origin to handle each request.

For example, a shop places its product images behind a CDN. A visitor in another region can receive a cached image from a nearby CDN location, while a request to submit an order still needs the shop's application to process current information. The CDN does not automatically replace the origin or cache every type of content.

Does a CDN always make a site faster or safer?

No. The benefit depends on geography, content, cache settings, and the CDN's network. A CDN can also provide services such as traffic filtering, but protection depends on the product and configuration. If the CDN cannot reach the origin, uncached or dynamic pages may fail even when cached files remain available.

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