What is a CDN?

Learn the ins and outs of content delivery technology.

Content delivery network

A content delivery network, commonly referred to as CDN, is a network of edge servers strategically placed across the globe with the purpose of delivering digital content to users as fast as possible. When a user makes a request it is routed to the nearest CDN edge server, which significantly reduces the latency. A CDN allows all users, no matter the geographical location, to have fast loading content for an unquestionably improved experience.

According to BuiltWith, 66% of the top 10,000 websites are using a CDN (November 2018). This percentage has continually increased over the last 10 years due to the large growth of digital content consumption and high user expectations. Utilizing a CDN is one of the most effective ways to deliver content with high performance and reliability on a global scale.

In fact, a study done by the University of Nebraska found that the tolerable waiting time for information is approximately only 2 seconds.

CDN architecture

Learn about the infrastructure behind a CDN.

At a high level, CDN architecture is made up of two key components, which are points of presence and edge servers. Beyond these there is a lot at work to allow traffic to be properly routed, attacks to be mitigated, and a continuous uptime to be maintained.

Points of presence

A point of presence, commonly referred to as a POP, is a single geographical location where a group of CDN edge servers reside. Whereas points of presence, commonly referred to as POPs, is multiple geographical locations that when combined make up the entire network. The total number of POPs that make up a CDN as well as each location has a large effect on the global coverage.

Edge servers

An edge server, which is a server that resides between two networks, are located at each POP. Edge servers are simple proxy caches that work similarly to a web browser cache. They do not generate content for the website, instead, they keep a copy of the content in the cache. The total number of edge servers located at each POP will vary for each CDN provider.

The dispersion of POPs will vary from CDN to CDN. Certain providers prefer to cover more ground with small-capacity servers, while other CDNs aim to maintain fewer, high-capacity POPs. One important aspect to take into consideration when analyzing a CDN's architecture is to find out where their POPs are located. Depending upon where a particular website's visitors are coming from, this could be a deciding factor.

How does a CDN work?

Learn the importance of getting content closer to the user.

As mentioned, a CDN is a large network made up of various servers located in multiple geographic regions. The POPs are placed close to populated areas, in countries all over the world. For large countries, there may be many different POPs.

The idea is to direct the user to the closest point of presence. When a user requests content from a site that uses a CDN, the request is routed to the closest POP, where a web server sends the requested data. There are several different ways that a request can be routed to a specific POP, one of which is IP Anycast.

Without a CDN

When a CDN is not used all content will be delivered by a single origin server no matter the geographical location of the request. This means that if an origin server is located in Switzerland users from both Australia and Canada will receive content from the same single location. The physical distance between the requesting location and responding origin server has a significant effect on the overall loading time.

With a CDN

When a CDN is used all content will be delivered by the closest POP from the geographical location of the request. This means that even if an origin server is located in Switzerland users from Australia and Canada will receive content from different locations. The shortened physical distance between the requesting location and responding CDN edge server significantly decreases the overall loading time.

Types of content

When analyzing the global population internet usage the types of content that consumes the most bandwidth are image, video, and audio files. However, there are many other types of content that a CDN can deliver. The supported content type and formats will vary for each CDN provider but here are some common supported formats:

  • Image: PNG, JPG, SVG, GIF, and TIF
  • Video: FLV, HSL, MP4, MOV, and WMV
  • Audio: MP3, WAV, AIFF, AAC, and PCM
  • Other: CSS, JS, JSON, HTML, PDF, ZIP, TTF, OTF, and WOFF

Why is a CDN needed?

Learn the benefits gained by using a content delivery network.

Improve performance

Increased performance is by far one of the most important benefits from implementing a CDN. Content is cached in POPs all around the world bringing content closer to the user. The shorter distance will not only reduce latency but also minimize packet loss. If users from all around the world are going to be accessing a resource, the use of a CDN is essential.Upon performing various tests in many geographical locations, we have seen a CDN reduce website latency by 73% on average compared to websites without a CDN.

Boost reliability

With a CDN, requests will always be routed to the nearest available location. If one edge server is not available, requests are automatically sent to the next available edge server. This creates automatic redundancy helping to ensure that content always remains available. Without this type of redundancy, visitors may be greeted by an error page which will greatly impact the chance that they will return.

Effortlessly scale

Offloading traffic to a CDN will make it easier to manage traffic spikes and scale up or down within a short amount of time. This will result in less load on an origin server and help minimize any downtime. Since a typical website is comprised of approximately 80% static content, a significant portion of web assets will be delivered faster and more efficiently from a CDN.

Increase security

When a CDN is used, the majority of traffic is no longer being served by the origin server, but rather by the CDN edge servers, allowing DDoS attacks to be automatically mitigated by the CDN. TLS certificates, commonly referred to as SSL certificates, can be implemented on most CDN platforms ensuring all traffic is encrypted. Morever, many CDNs also have additional security features such as hotlink protection, secure tokens, and more to protect against third-party access.

Lower costs

With a CDN there is no infrastructure to manage because this is handled by the CDN provider. This eliminates any upfront investments and maintenance costs and allows time be prioritized elsewhere. Origin server bandwidth costs are reduced because content is delivered by CDN edge servers instead. Therefore, there is less need to upgrade to a stronger hosting plan due to the fact that it will be serving less traffic thanks for the cached content on the CDN's edge servers.

Raise conversions

There have been many proven cases that increasing the overall speed of a website, game, or any digital content will raise conversions. This occurs primarily because the user experience is improved. According to LoadStorm, just a 1 second delay in load time will on average lead to a 7% loss in conversions. Using a CDN can increase conversions to achieve higher sales goals.

Reduce abandonment

There are many factors that contribute to a high bounce rate, like the navigation, appearance, and usability. One of the most important factors is the total time it takes for content to load. According to Web Performance Today, 57% of online consumers will abandon a website that takes more than 3 seconds to load. Using a CDN can increase user engagement by reducing abandonments. This in turn helps improve your ranking in search engines, increase sales or conversions, and improve the overall user experience.

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