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Cloud Architecture Patterns by Bill Wilder

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Chapter 14. CDN Pattern

This pattern focuses on reducing network latency for commonly accessed files through globally distributed edge caching.

The goal is to speed up delivery of application content to users. Content is anything that can be stored in a file such as images, videos, and documents. The Content Delivery Network (CDN) is a service that functions as a globally distributed cache. The CDN keeps copies of application files in many places around the world. When these places are close to users, content does not need to travel as far to be delivered, so it will arrive faster, improving the user experience.

CDN nodes are strategically located around the globe, hopefully close to application users. The CDN has its own URLs that are resolved by a geographic load balancer that directs users to the nearest node, regardless of where the user is.

The flow of files is shown in Figure 14-1. When a CDN URL is requested for the first time, the CDN will retrieve the file from the main source (usually known as the origin server), and then return that to the requesting user while also caching a local copy to satisfy subsequent requests for that file. When a CDN URL is requested and the file has already been cached, the CDN returns a locally cached copy of that file to the requesting user. This is faster than if the user retrieved it from the origin server, which is (presumably) further away. When many users access the same content from a CDN node, the initial request is slower (so the first ...

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