Content Delivery Networks

Content delivery networks (CDN) are the transparent backbone of the Internet in charge of content delivery. Whether we know it or not, every one of us interacts with CDNs on a daily basis; when reading articles on news sites, shopping online, watching YouTube videos or perusing social media feeds.

No matter what you do, or what type of content you consume, chances are that you'll find CDNs behind every character of text, every image pixel and every movie frame that gets delivered to your PC and mobile browser.

To understand why CDNs are so widely used, you first need to recognize the issue they're designed to solve. Known as latency, it's the annoying delay that occurs from the moment you request to load a web page to the moment its content actually appears onscreen.

That delay interval is affected by a number of factors, many being specific to a given web page. In all cases however, the delay duration is impacted by the physical distance between you and that website's hosting server. A CDN's mission is to virtually shorten that physical distance, the goal being to improve site rendering speed and performance.

How a CDN Works

To minimize the distance between the visitors and your website's server, a CDN stores a cached version of its content in multiple geographical locations (a.k.a., points of presence, or PoPs). Each PoP contains a number of caching servers responsible for content delivery to visitors within its proximity.

In essence, CDN puts your content in many places at once, providing superior coverage to your users. For example, when someone in London accesses your US-hosted website, it is done through a local UK PoP. This is much quicker than having the visitor's requests, and your responses, travel the full width of the Atlantic and back.

This is how a CDN works in a nutshell.

CDN BUILDING BLOCKS

PoPs

(Points of Presence)

CDN PoPs (Points of Presence) are strategically located data centers responsible for communicating with users in their geographic vicinity. Their main function is to reduce round trip time by bringing the content closer to the website’s visitor. Each CDN PoP typically contains numerous caching servers.

Caching Servers

Caching servers are responsible for the storage and delivery of cached files. Their main function is to accelerate website load times and reduce bandwidth consumption. Each CDN caching server typically holds multiple storage drives and high amounts of RAM resources.

SSD/HDD + RAM

Inside CDN caching servers, cached files are stored on solid-state and hard-disk drives (SSD and HDD) or in random-access memory (RAM), with the more commonly-used files hosted on the more speedy mediums. Being the fastest of the three, RAM is typically used to store the most frequently-accessed items.

References https://www.incapsula.com/cdn-guide/what-is-cdn-how-it-works.html