What is a Content Delivery Network (CDN)?

Written by
Last Updated: Mar 11, 2021 | Published: Mar 7, 2021

Have you ever wondered how websites from the UK or Australia can deliver content to you in less than a second? The secret is a content delivery network (CDN): a server system that allows websites to provide content at consistently fast speeds. CDNs have been around since the late 90s, but you’re probably just now hearing about them because of our rapidly increasing internet usage.

Whether you’re a curious internet user or a current or soon-to-be website owner, we created this guide to make sense of what a CDN is, how it works, and why significant websites like Netflix use one.

What is a CDN?

Global network

A CDN is a network of servers dedicated to delivering content as fast as possible between internet users and websites. You can think of a CDN like a wire transfer service for websites — they allow users to access content from a server closest to their location.

Say you live in New York and you visit a website whose servers are based in Australia. If that website uses a CDN, it will send its content to that CDN. The content will then be available at any of the CDN’s servers across the globe (like money would with a Western Union or MoneyGram transfer). Rather than having content delivered from the website’s main server, you’ll have the content sent to you from the nearest server belonging to its CDN.

Why are CDNs used?

The overall goal of a CDN is to improve a website’s performance. While speed is essential to keep new and returning visitors engaged, website owners implement CDNs for several reasons:

  • Reduced stress on servers: Information on the internet is stored in servers, and each server has its limits to how much traffic it can handle. The more traffic, the more likely a server is to slow down or crash. Websites can minimize their (or their host’s) servers’ workload by funneling content requests through CDNs. This is important for website owners since servers and web hosting can get costly, but also for everyday internet users who don’t want to run into “cannot connect to server” error messages.
  • Increased reliability: Since CDNs have servers in multiple locations, users can receive content from any of the locations closest to them. If the server closest to you doesn’t have the content you requested (or is down), your request will get sent to the next nearest server. Having a wide reach of servers makes it easier to ensure users get content at high speeds while still reducing a website’s servers’ workload.
  • More secure browsing: Some CDN providers can encrypt data sent to and from their networks, adding another layer of protection for websites and internet users. In a way, CDNs can act as a filter for certain types of cyberattacks, especially ones that attempt to shut down specific websites or servers (i.e., Distributed denial-of-service (DDoS) attacks).
  • Reduced latency: As we mentioned, cutting down travel time is the main reason websites use CDNs. Streamers and gamers know how frustrating lagging (high latency) is. No matter how well-designed a website is or how fun a game may be, websites can quickly lose traffic if their content takes “too long” to load.

How do CDNs work?

CDNs can improve website performance by saving copies of website content to edge servers located in different countries and continents. These edge servers, or servers that connect other networks, are located at points of presence (PoPs).

The number of PoPs varies by CDN provider. However, the delivery of content is the same no matter where their PoPs are located. When you visit a website that uses a CDN, a data request is sent to the nearest PoP rather than the website’s server. The closer you are to a PoP, the faster your request is processed, and your content is delivered.

Internet usage has grown so much that some websites are using multiple CDN providers to ensure all their visitors can have the same, fast experience. The number and strength of PoPs are key factors website owners consider when shopping for CDN providers since they directly affect latency on the user-end. The partnerships CDN providers have with each other are also a factor thanks to CDN peering: the mutual exchange of internet traffic between CDN providers allows websites access to an even wider range of PoPs.

What CDN providers are there?

It is no surprise that most internet users have no idea which CDN provider their favorite websites use. There are hundreds of CDN providers, most of which you’ll probably never come across unless you plan on having your own website one day. As an internet user, however, knowing which CDN(s) route your traffic can give you a high-level view of how your data is transferred throughout networks and of the level of security your favorite websites provide.

In the US, more than 99 percent of US-based websites are distributed through just 10 CDN providers. We list the top 10 most used CDN providers in the US in the following table; however, if you plan to or currently own a website, take a look at our Best CDN Providers guide for an in-depth review of each provider.

Provider Price (US pricing) # of PoPs
Amazon CloudFront $0.02-0.085 per GB + $0.01 per 10,000 HTTPS requests + $0.0075 per 10,000 HTTP requests 225+
OVH CDN $2.49 per month 19
Cloudflare $0-200 per month ~224
Akamai Varies Not disclosed
Imperva (Incapsula) CDN Varies 47
Fastly $0.08-0.12 per GB + $0.0075 per 10,000 requests 64+
Section.io $395-595 per month 60+
BunnyCDN $0.01 per GB (for full network access); $0.0025-0.005 per GB (for partial network access) 49
Microsoft Azure $0.023-0.081 per GB 170+
ArvanCloud $0-0.061 per GB + $0.0015 per 10,000 requests (First 50 GB and 1 million requests are free each month) 40

How much do CDNs cost?

CDNs can get costly depending on how much traffic a website receives, how much data their visitors upload/download, and where they need their content sent. CDN providers like Amazon Cloudfront and Fastly have tiered pricing, meaning their prices decrease as traffic volume increases. Tiered pricing models typically charge by bandwidth used and the number of requests for data sent to/from a website. For example, Fastly charges $0.12 per GB for the first 10 TB of bandwidth used and lowers their price to $0.08 per GB for the next 10 TB. On the other hand, CDN providers like Section.io and Cloudflare have simpler pricing models, offering various plans priced at a flat-rate monthly fee.

If your website has different needs than your preferred CDN provider’s plans, you can create a custom plan. Each of the above providers allows website owners to create customized plans, but some require a minimum monthly traffic before allowing special plans. The good news for everyday internet users is that CDNs are paid for by website owners.

While a CDN’s cost can easily exceed $500 a month, the payout may be worth it. According to Google, more than half of mobile internet users leave a website that takes more than three seconds to load. E-commerce businesses like Shopify rely on CDNs to prevent losing customers and increase sales while streaming providers like Netflix use CDNs to provide a buffer-free streaming experience.

Websites currently using CDNs

The majority of websites we visit daily use one or more CDN providers, depending on where their users reside. Since CDNs only secure the data coming to and from their networks, most websites also use a virtual private network (VPN) for an extra layer of protection.

Think of a VPN as a gated backroad. VPNs route your data through a protected network allowing users to browse the internet anonymously and free from censorship. Your data can become more vulnerable to cyber attacks as it travels through multiple servers. Websites use VPNs and CDNs to ensure all traffic and data shared to and from their visitors travel through a protected network. Take a look at the following list to see which CDNs and VPNs the top 20 most popular websites in the US use.