How CDNs Use Client-Side Code to Speed Up Web Downloads

Amazon's patent on using client-side code like JavaScript to dynamically rewrite website links so they point directly to the fastest content delivery server, bypassing traditional DNS routing bottlenecks.

What it covers

The patent describes a system where a Content Delivery Network or CDN provides executable code to a user's web browser. When the browser loads a webpage, this code runs and requests translation information from the CDN for original URLs embedded in the page. The CDN determines the best server source based on factors like regional plans or service levels, and sends back translation rules. The browser then rewrites the original URLs into optimized URLs pointing directly to the CDN's chosen server and fetches the assets. For example, a standard link like 'example.com/image.png' is dynamically rewritten by the browser into a CDN-specific link like 'cdn-region1.service.com/image.png' before the browser makes the request.

What it doesn't cover

• —Does not cover traditional DNS-based redirection where the domain name resolution itself redirects the user without client-side code execution.
• —Does not cover URL rewriting performed entirely on the origin server before the webpage is sent to the client.
• —Does not cover static URL structures where links are hardcoded and never dynamically translated or updated by client-side scripts.
• —Does not cover client-side translation that does not involve requesting translation rules from an external service provider.

The clever bit

Instead of relying on DNS servers to guess where a user is located, the system uses the user's own browser to ask the CDN for a personalized routing map, dynamically rewriting the webpage's links on the fly.

Why it matters

In high-performance web hosting, routing users to the nearest server is critical. Traditional DNS routing can be slow and is often cached incorrectly by internet service providers. By moving the routing logic into the browser using JavaScript, CDNs like Amazon CloudFront can bypass DNS limitations, making websites load faster and allowing real-time traffic management based on service tiers or regional outages.

Real-world examples

• 1.Amazon CloudFront CDN routing
• 2.Dynamic client-side asset optimization in modern web applications
• 3.Edge-computing-driven URL rewriting in browsers