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Content Delivery Networks Explained

Content Delivery Networks Explained

16 December 2021

Content delivery networks (CDN) are an ever-growing, ever-more-integral tool in web hosting and online content delivery (as the name suggests). In essence, CDNs are groups of servers spread out across the world that cache web content and allow it to load more quickly; they also offer other fringe benefits like reduced bandwidth use (and therefore hosting costs) and enhanced security against some types of cyber-attacks, most notably denial-of-service actions. However, CDNs aren’t perfect. They introduce some new weak points in content availability and, as is often the case with new links in a distribution chain, can cause some unique problems that wouldn’t otherwise manifest.

While we do not offer CDN services at IDMI, it can be useful to understand a little bit about them and how they work—including the ways they can cause outages that are unrelated to other links in the chain, like hosting or design.

What Do Content Delivery Networks Do, Exactly?

Modern websites and apps have more raw content (images, text, video, audio, etc.) than ever before, largely thanks to high-speed internet becoming increasingly commonplace around the globe. But even the fastest networks can be bottlenecked by distance; a user in Illinois or Georgia won’t be able to load data from a host server in California as fast as a user in, say, Nevada. The larger the distance between the end-user and the origin point of the content, the longer the load times.

Content delivery networks help to mitigate those issues by caching content on servers distributed evenly across a geographic region. That means that users can load some or all of a site’s data from the closest exchange point, not the originating host server—and that translates to smoother, more normalized load times for users regardless of their proximity to the host. In a world where speed is king and most users have little patience for long load times, the importance of CDNs is clear.

So, What Can Go Wrong?

Two frequent complaints about content delivery services are that they can cause downtime or slow loading themselves when one or more of the exchange points has an issue, and that they can strongly inhibit frequent/real-time content updates because changes must pass through a service provider (which can potentially make time-sensitive updates irrelevant).

The first of those issues is self-evident. CDNs are just server networks, and those servers can, like all others, see downtime for any number of reasons—power outages, the failure of backup generators that are meant to provide continuity of service in case of power outages, damaged or otherwise non-functioning hardware, necessary maintenance, and so on. CDNs also introduce new software failure points in the delivery chain; forcing cooperation from diverse code that was never intended to work together often creates deep-seated, unforeseeable bugs that survive the testing.

The second issue is a bit more niche, but it still applies to a large swath of extant websites. When a site is loaded wholly from the host, changes made by editors and designers can go live as soon as they’re reflected in the server data. When a CDN is involved, changes to a website don’t go really go live until they’ve passed through the service provider and hit all their exchange points. Depending on the responsiveness of any specific provider, that process could take long enough to make real-time or frequent updates impossible (or very difficult).


Content delivery networks are important tools for building a seamless web experience, but they aren’t without their downsides or limitations. Understanding what they do and in what ways they can be frustrating is important for managing your expectations properly.

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