What is a CDN – Content Delivery Network?

A content delivery network allows web pages to load faster by using servers that are geographically close to the visitor of the web page to answer requests.

What does a content delivery network do?

The main purpose of a content delivery network (CDN) is to make web pages load faster worldwide. This is achieved by storing (caching) static website content (for example, JavaScript and CSS files, as well as images) on many servers distributed around the world.

This makes it possible to send these cached resources to a website visitor from a server near him, which can massively accelerate the page loading speed.

Example of a web page request without a CDN

If I try to access the homepage for www.sistrix.de from Australia without using a Content Delivery Network, the requests would have to travel all the way from Australia to Germany (as our servers are located in Germany) and back again. The complete retrieval of the page, without a CDN, could take 10 to 20 seconds.

This would involve several round trips between Germany and Australia, which is almost 14,457 kilometres away. A site visitor could, of course, be impressed by how fast data travels over the World Wide Web. Unfortunately, it is more likely that said visitor will jump back to the search results or go to another page after waiting for a few seconds.

The world has become fast-paced and visitors expect websites to load quickly. This is even more true of mobile users.

Example of a web page load via a CDN

Let’s take the above example and include a content delivery network along the way, which has the static components of our site stored on a server in Australia. In this case, the page can load in one to two seconds, as our Australian visitor’s browser can retrieve much of the content from a much closer server.

Advantages of a CDN

The speed advantage of a content delivery network can be enormous, and this can also be clearly measured in terms of user satisfaction.

In addition, the saved bandwidth no longer has to be paid for by the user’s internet service provider. The prices charged by the CDN provider for transferring the data are, of course, also taken into account.

Disadvantages of a CDN

For the website operator, the use of a CDN initially involves more effort. The requirements that a website or service places on a content delivery network need to be clarified, and a CDN provider must then be found that meets those requirements.

CDN and dynamic content

Dynamic content, such as news tickers or shopping baskets in an online shop and other requests that need to access one’s own databases, are not suitable for caching and thus cannot be stored and displayed via a CDN.

In recent years, content delivery network providers have not found a solution to this problem, but they have found a way to help. Under the acronym DSA (Dynamic Site Acceleration), they summarise various practices that can enable the CDN to improve the loading time, even when displaying dynamic content.

Advantage for search engine optimisation

From a search engine optimisation perspective, faster loading times are always a good idea. The more Google pays attention to user expectations, the more important it becomes to meet them.

Disadvantage for search engine optimisation

If the web operator does not have their own CDN, their content is hosted on third-party servers. This means that SEOs must keep an eye on all changes that occur in order to ensure that all resources on the CDN are kept up-to-date. This is especially important if US servers are being used, as they are likely to handle requests from the Googlebot – and these almost always come from US data centres.

So if, for example, you optimise the snippets, it is no longer sufficient to make sure that Google crawls the page again; you have to make sure beforehand that the changes have been adopted by the CDN.


As soon as your visitors come to you from a variety of different regions around the world, it is a good idea to weigh up the advantages of a content delivery network with the possible disadvantages and costs.

The setup and configuration is supported by many CDN providers and can often be achieved via drag-and-drop front-end interfaces. Unfortunately, there is no getting around the fact that a certain technical understanding is required here.

Steve Paine