Content Delivery Network (CDN)

A content delivery network (CDN)A content delivery network (CDN) is a network of distributed servers that delivers static content closer to the user, reducing loading times.Open glossary entry → is a network of geographically distributed servers that delivers content such as images, CSSCascading Style Sheets (CSS) is the language used to define the layout and design of web pages. CSS controls colours, fonts, spacing and arrangement, among other things.Open glossary entry →, JavaScript and other static assets as close as possible to the user's location. This shortens transmission paths and loading times and relieves the origin server.

A CDN is an important lever for server response and therefore indirectly affects Largest Contentful Paint (LCP)Largest Contentful Paint (LCP) measures when the largest visible content element in the viewport has loaded, representing the perceived loading speed.Open glossary entry →. The absence of a CDN can be one cause of slow loading times. Typical use cases include:

• delivering static assets such as images, CSS and JavaScript,
• edge cachingCaching stores previously retrieved content so it is available faster on repeat requests, relieving both servers and the network.Open glossary entry → of content closer to the user,
• faster delivery for international audiences.

However, a CDN does not replace fundamental optimisation: if images are too large or JavaScript blocks renderingJavaScript rendering is the process by which a browser or crawler executes JavaScript code to build the final, visible page. Content that is not already in the delivered HTML only appears after this step.Open glossary entry →, a CDN can only help to a limited extent. It is one building block alongside caching, image optimisationImage SEO covers all measures that make images more understandable for search engines, image search and machine systems. This includes alt text, descriptive file names and suitable context.Open glossary entry → and lean front-end code.