What is a CDN?

The most basic answer is, a CDN, or “Content Delivery Network” is a network of web servers strategically located near end users to accelerate the delivery of websites, emails, documents, videos, etc.  CDN’s are a cache (“copy”) of content only; they are not publishing platforms or cloud storage.

Is a CDN just Web Hosting?

Whereas a web host or asset store (S3) are not designed for performance and scalability, a CDN is a design to extend the performance, security, and scalability of those platforms.

Web hosting or Asset Hosting (such as S3) typically refers to file hosting on a specific server or group of servers in a specific geographic location.  For example, S3 may host your content in Portland, Oregon, United States. By contrast, a CDN has multiple locations strategically placed to be “near” your end users. CDNs typically read and then store a copy of the content from a web host (an “Origin”) so that further requests may be serviced from the CDN (“offloading” or “content shielding”).

There are many other differences and benefits of using a CDN as well, some of which we’ll cover further below.

Milliseconds Matter

Loading time costs you money. Studies from Google, Amazon, and many others show every millisecond counts, and shaving offload time will directly increase conversion and usage. The longer your content page takes to load, a PDF takes to open, or an email takes to render, the higher the likelihood that a customer abandons it. In essence, no one likes to wait for something to load, and people have short attention spans. An excellent CDN to accelerate your content is critical. Fast has a network 219,000 servers at 7,100 locations in 130 countries; our CDN is always close to every end user.

Why are CDNs effective?

There are two primary factors, 1) the physical distance between the end user and the server they are connecting to, and 2) the capacity of the server or cluster of servers.

The physical distance is so significant because the speed which a video, image, website, or download occurs is a function of throughput.  Throughput is heavily dependent on delays (“latency”) and the simplest way to reduce latency is to put the server as close to the end user as possible. That’s why Fast has 200,000+ servers in more than 7,000+ locations around the globe.

The other factor is that putting your content on a single server or location limits availability to the capacity of a single server. A CDN has many servers and distributes load across them automatically, providing redundancy, scalability, and performance. Since Fast has more than 200,000 servers, we can provide as much capacity as you need.

Mobile Growth

Mobile devices, including smartphones and tablets, outnumber desktop computers even today. Cellular devices are also far more sensitive to latency than desktops computers which causes content loads more slowly. Having your content cached as closely to mobile users as possible makes the largest difference in load time and end-user experience. Fast also supports other technologies aimed at further decreasing load time, such as HTTP/2.

Points of Presence

CDNs typically work in one of two models: the Mega-pop or the Micro-pop models. The Mega-pop model is easier to accomplish, a CDN creates a small number of very large POPs (“Points of presence” or “Datacenters”) that do a very large amount of traffic. There are fewer sites to manage and it’s more centralized. The downside is that you are never as close to customers as you can be with the micro-pop model. For Example, if a CDN has one Mega-pop in China, it will never perform as well as 50 micro-pops in China just because of physical distance. The micro-pop model, as you might expect, is comprised of many small pops (or datacenters) in an attempt to get as physically close to customers as possible.

To put this in perspective, popular CDNs CloudFlare and Amazon CloudFront have 152 pops and 32 pops, respectively. Fast, which runs on Akamai’s micro-pop network, has more than 7,100 pops.

How does a CDN Work?

CDNs are configured to read content from origins, which are typically assets stores or web servers. When an end user makes a request, it’s made to the CDN. The CDN in turn makes a request to the origin and then caches the origin’s response (stores it for a period of time). The response is also relayed to the end user so, to the end user, the request appears to have been served by the web server. The next request that is made to the CDN for the content is served from the CDN without contacting the origin.

Fast reads your content from your Cloud Storage instead of from a web server providing the same benefits as traditional CDN but allowing you to manage your content directly from your Cloud Storage (Box, Dropbox, Google Drive, and OneDrive).


CDNs have the added benefit of increasing the reliability and availability of your content. A traditional web server or asset store (S3) have single points of failure, but CDNs are designed to be massively redundant for scalability and performance.

How Fast Differs

Fast has all the benefits of a traditional CDN with the advantage of using Cloud Storage as an origin instead of a web-server or asset store. This benefits you in a number of ways, including 1) being able to keep the same workflow you already use to manage, create, and collaborate on content, 2) not having to re-deploy content to another location, and 3) automatic deployment of updates.

Fast offers 50GB per month of free transfer. That’s enough data to deliver a 1MB image 50,000 times a month without cost. Get started in minutes.

More information

Want more detailed information about how a CDN works? Check out this great presentation by Shaxun Chen from 2009. If you have more questions, we’re here to help, contact us!

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