Definition

A content delivery network (CDN) is a network of servers, distributed across many geographic locations, that is optimised for delivering web content quickly. Rather than every request reaching a single origin server, a CDN serves cached resources from a server near the user.

CDNs improve delivery through three mechanisms: proximity, where servers nearer the user reduce round-trip time; caching, where resources are stored on CDN servers and pulled from the origin only when needed; and optimised routing between CDN nodes. By reducing latency and offloading traffic from the origin, a CDN can improve Time to First Byte and may help Largest Contentful Paint, and it helps a site absorb traffic spikes. CDNs serve static assets well, and many can also cache or accelerate dynamic content.

Examples

• Static asset delivery

  A website serves its images, CSS and JavaScript through a CDN, so a visitor in another country receives them from a nearby edge server instead of the origin.

• Handling traffic spikes

  During a product launch, a CDN absorbs most requests from cache, reducing load on the origin server and keeping response times stable.

Sources

• web.dev — Content delivery networks (CDNs)
• web.dev — Optimize Time to First Byte

Related terms

• Time to First Byte
  A performance metric measuring the time between a request for a page and the first byte of the response arriving back at the browser.
• Page Speed
  How quickly a web page loads and becomes interactive, measured by metrics such as Largest Contentful Paint, Interaction to Next Paint, and Time to First Byte.
• Largest Contentful Paint
  A Core Web Vitals metric measuring how long the largest visible content element on a page takes to render after loading begins.
• Core Web Vitals
  A set of three Google metrics that measure real-world page experience: loading speed, interactivity and visual stability.
• HTTPS
  Hypertext Transfer Protocol Secure — the encrypted version of HTTP. Google uses HTTPS as a lightweight ranking signal.
• Resource Hints
  Markup that tells the browser about connections or resources a page will need, so it can prepare them ahead of time.

Where QueryCatch uses this

• SEO Audit
• Page Optimisation