It is called Content Delivery Network, or CDN, and it is literally a network for delivering multimedia content, or rather, it is an infrastructure of various servers located and extended globally that are tasked with distributing these resources over the Internet. We talked recently about this network, especially in relation to the improvement of the performance of the site and user experience, and Google also recommends its use to achieve the quality objectives provided by the Page Experience Update coming soon: So let’s try to define the CDN and discover its positive features for the SEO.

What is a CDN

A Content Delivery Network or CDN is a platform composed of various servers and highly distributed geographically and network, which has the function of distributing via the Internet some content of particular and heavy sites, such as image files, videos, audio, HTML files, CSS and Javascript, to decrease the physical distance between the server and the user and reduce the delay in loading such resources.

Thanks to the CDN, users around the world can view the high-quality content of a site without delays in loading, with positive effects on user experience and benefits for the site as well.

How works the Content Delivery Network

To understand how a CDN works, let’s first look at the classic situation for sites that do not use this system.

The distribution of content without CDN is based on a single server, which must provide answers to every request of visitors to the site, whether they are located in the immediate geographical vicinity, or located on the other side of the world. This results in a high source traffic, which therefore generates a significant load that can make it more likely a failure of the original server, especially in situations of peak traffic or persistent load.

In contrast, the CDN consists of multiple servers that respond to requests from end users from the nearest physical and network location to their location. In this scenario, the content is stored in several places simultaneously, ensuring a wider geographical coverage that reduces the distance for data transfer and, in this way, lowers waiting times for users.

Understanding CDNs

For example, without a CDN if a UK user wants to view the contents of a web page hosted on a server in the US, the loading times will be long because the request has to cross the entire Atlantic Ocean. Through the use of a CDN, however, the answer to the user will come from the server closest to its location, with significant time savings and no negative effects on quality.

A CDN network acts essentially as a multi-route traffic intersection to which different providers and Internet servers can connect and provide each other with access to website traffic from each source. A CDN transmits resources and traffic back and forth as resources are called from page loads, instead of waiting for each resource to be loaded onto individual pages or rendering as a hard-coded element. In addition, this process happens worldwide in multiple locations, unlike the “old system” to rely on a single server for all services and delivery of content; to further reduce the loading time and delivery path, These server hosts keep files cached ready for rendering when they are called.

The architecture of CDNs

Simplifying, the Content Delivery consists of a web server of origin (Content Provider or Origin Server) and all the Edge Servers (also called Content Servers or Delivery Servers, or the servers on which the contents are replicated), and this can also reach an extended size of a few thousand nodes (distributed over tens of thousands of servers).

Each server stores or caches copies of a subset of Web content (HTML files, images, audio, video, applications) from the host server in multiple geographic areas of the world, known as Pop (Point of Presence). Each Pop has its own caching servers, which concretely allow you to distribute the required content according to the user’s location.

The heart of this process is the Request Routing, which directs requests to Edge Servers and also establishes how the contents are replicated, and then sent, to users.

CDNs are capable of serving a very wide range of content, including high-quality images and videos, audio streams, software downloads (apps, games and OS updates), data records containing medical and financial information, and “potentially any digitized piece of data can be distributed via a CDN” (Akamai).

The process of content distribution

Site owners can contact a CDN service provider (such as Akamai, a world leader in the field) to have the ability to distribute website content to each server in the network.

These servers store cache versions of the site’s content, making it immediately available for user requests. When a user requests a page, in fact, the content is delivered via the server geographically closest to him, identifying copies of web content closer or facilitating the delivery of dynamic content (as in the case of live video feeds).

The advantages of a CDN for both site owners and users

In this way, the physical distance between the content and the users is minimized and, therefore, the latency is reduced, which represents the delay between the forwarding of a request on a web page and the completion of the loading of the same on the device in use.

But Cdns also improve loading speed and user experience, because they optimize delivery based on the type of content required – standard web content, dynamic content, video streaming or downloading large files – and also increase bandwidth and reduce overhead costs for servers.

No less important is the security aspect: content distribution networks use analytics and automation tools that can detect DDoS attacks (Distributed Denial of Service), man-in-the-middle attacks, firewall problems and others, and so increase the security of the server, data and applications in use.

Ultimately, then, Content Network Delivery helps the publisher of a site to provide faster performance, reduce loading times for its users, control bandwidth consumption, avoid or fix overloaded server problems and reduce costs, both traffic and economic.

Why choosing this solution

The average Web user “does not care about how web pages work or the web hosting provider used by a company, and all that interests them is their user experience, intended primarily as upload speed, quality content and intuitive navigation“, comments Kevin Rowe on Search Engine Journal.

Speed means money, and this is especially true for e-commerce sites, and various studies show that pages that load within 0-2 seconds have the highest e-commerce conversion rates. In addition, conversion rates decrease by an average of 4.42% with each additional second of loading time between 0 and 5 seconds.

Even for non e-commerce sites, page load rates determine profits, because they can affect the bounce rate: sites that load in 1 second have an average bounce rate of 7%, while pages with a 3-second page latency have a bounce rate of 11% and those that take 5 seconds rise to 38% of rebound.

In all sectors, then, the use of CDN is a standard strategy to achieve optimal page loading speeds for both desktop and mobile devices: a Cisco research shows that global CDN networks are expected to transport 72% of all Internet traffic by 2022, and it is “almost impossible now to meet user expectations and compete with competing sites without using CDNs”.

This is especially true in view of the now coming Page Experience Update, which will make ranking factors the Core Web Vitals (and other technical parameters related to the user experience on the page) and therefore requires to verify the performance of the site on elements such as loading, interactivity and visual stability. And Google has expressly recommended the use of CDN for SEO, both for image optimization and for the improvement of the LCP, the largest contentful paint that is one of the essential web signals examined by the search engine.

How to choose a CDN: characteristics to evaluate

A text by Rachel Vandernick accompanies us to the crucial features to look for in a CDN solution.

The most important aspect is obviously speed: the CDN network must be faster than our current origin, otherwise there would be no benefit in the change. In addition, we need to make sure that it works well in providing small files and large payloads in the same way.

Among the main common metrics that we can test and explore in a demonstration test of the network there are:

  • DNS response time to the last mile and end user. Useful to avoid that the implementation of a complex DNS configuration can create long waits for end users.
  • Performance during peak hours. If our site undergoes large traffic fluctuations based on the days of the week or the hours of the day, it is advisable to test the CDN response at the most appropriate time.
  • Connection time. It is used to check if there are basic requirements such as network connectivity, low latency and zero packet loss.
  • Waiting time on less popular resources. CDNs are a shared environment and it is important to know if the least requested resources are recovered from the source server compared to those served by the edge (such as popular resources).
  • Cache Hit / Miss. It is not a good sign to notice many requests that return to the origin.
  • Effective Range. The throughput value should not be lower than the origin for assets of any size.
  • API integrations. It is good to choose a CDN that, even in the future, can be configured with the existing software or that we will develop.

More specifically, in choosing an efficient CDN provider we need to assess whether it has a wide and diverse network and know the location of its servers, to check whether it meets the needs of our target audience, both current and potential new markets.

But how much does a CDN network cost? According to US information, sites of medium-sized companies can expect to pay about 200 dollars or more per month for a solution based on their needs, while usually the solutions for enterprises of greater dimensional level are almost always personalized and customized.

CDN and SEO, why the use of a network is important

It is clear from what has been written that the choice of a CDN network is becoming increasingly urgent and unavoidable for sites with high demand traffic or requiring a global presence, and more generally is an absolute priority for SEO professionals and entrepreneurs who want to ensure an effective loading speed for the pages of their projects.

Today more than ever the UX and SEO are intrinsically intertwined, but it’s actually long since Google considered the UX elements to determine the search rankings; the current advantage is that Google has already clarified exactly what metrics it will monitor and, so which ones we need to improve.

In addition to the benefits already described, premium CDN providers also include analysis reports and insights as part of the package: CDN networks can, in fact, collect and report critical information such as audience analysis, Query-based geographic traffic data, service quality data, security event analysis, and viewer diagnostics, all useful indicators to study to improve site performance.

As said, then, the use of a CDN network also affects the security of the site, because it protects sites from denial-of-service attacks (Ddos): by distributing content to numerous servers, the network prevents Ddos attacks from hitting the original server, and even if a server within the network is attacked or receives more traffic than it can handle, the request will be redirected to another server. These security aspects can have indirect positive effects on SEO, because they improve the user experience and create trust in the site or brand.

The potential pitfalls of a CDN for the SEO

Given these advantages for SEO, however, the use of a CDN network can also lead to potential disadvantages for a site, as highlighted in Rowe’s article.

First, “well-known figures in the SEO industry have questioned the impact of using CDNs on image rankings“, especially in the case of hosting images on a CDN domain or a subdomain of the website. However, “the best thing you can do to take advantage of image SEO is to still set up your CDN with a custom subdomain related to your main domain”.

Another suggestion is to “set a record or CNAME alias to clear the CDN subdomain name” and to recover link equity “by contacting sites that use your images but connect to the image source (the CDN) or image itself instead of your site” and asking their editors to edit the URL.

Another pitfall concerns duplicate content, but you just need to set up the CDN network properly to have no problems and, in particular, setting a canonical header that communicates to Google crawlers that the content on the CDN is a copy of the original.