A CDN (Content Delivery Network) is a geographically distributed and interconnected network of servers that work together to allow faster transfer of assets required for loading content, such as HTML pages, images, videos, and JavaScript files.
Also known as Content Distribution Networks, CDNs introduce a number of intermediary servers at strategically located data centers that store and deliver cached content. Their main goal is to reduce the physical distance between the website’s “origin” server and the end user.
Here’s an example of CDN in action:
Let’s say a website’s origin server is based in Japan. If a user from the EU wanted to access it, the CDN would serve them from an edge server located in the EU. The content is delivered from the proxy server that’s physically closer to the user - rather than the “origin server” in Japan.
Content Delivery Networks were first introduced in the late ’90s. So, the “evolution” of CDNs can actually be split up into three distinct generations:
Some of the leading providers of CDN solutions today include CloudFlare, Akamai, CDN77, and Amazon CloudFront, to name a few.
If the user accessed a website without CDN, the browser would connect to the site’s origin server and request content.
However, with a CDN, the browser requests content from one of the “edge servers,” typically the one closest to the user. The edge server then forwards the request to the origin server and, after receiving the data and delivering it to the user, caches the files for all subsequent requests.
CDNs store a cached version of the content in several geographical locations worldwide, known as Points of Presence (PoPs), at once. Each of these PoPs contains a number of proxy servers responsible for communicating with the users in their vicinity and reducing the distance that content must travel to reach them.
When the user wants to access a website, the CDN can dynamically calculate which of the CDN edge servers is the nearest to them - and deliver content based on that.
The main role of Content Delivery Networks is to reduce website load times by ensuring that the content is delivered from the edge servers that are closer to the end-user. But, as important as it may be, improved user experience is not the only benefit of using a CDN.
It also plays an important role in load balancing. Suppose a website experiences a sudden surge in web traffic. In that case, CDNs can help distribute these requests across multiple servers to avoid overloading one of the servers or impacting the website’s performance.
Then, there’s improved availability:
Even if the origin server crashes, the CDN will continue to serve cached content from one of the available edge servers, which ensures uninterrupted service.
Finally, CDNs also play a role in improving website security:
The same process that the Content Delivery Network employs to manage traffic spikes makes it resistant to certain cybersecurity threats, including Distributed Denial-of-Service (DDoS) attacks.
Even more so, a CDN can help protect the website through the Web Application Firewall (WAF). It analyzes and channels traffic to and from a website, examining each HTTP request and blocking questionable traffic, preventing threats like cross-site scripting (XSS) and SQL injection attacks.
Understanding CDNs is challenging, as it requires a certain degree of technical knowledge. That is why there are some misconceptions about them, one of which is the impact of CDNs on SEO.
Generally speaking, using CDNs has no effect on the website’s ranking. However, CDNs do improve the website’s performance, mainly the loading speed - which, in turn, improves the user experience and leads to better Core Web Vitals scores.
There were also some concerns that hosting images on CDN domains, rather than the website’s domain, would potentially harm their ranking in organic search results.
However, that myth has been busted:
From what Google’s representatives have said so far, whether you use the same domain to host images makes no difference SEO-wise and has no impact on how these images rank. The only advantage of hosting photos on the same domain is that it would make the process of switching CDNs more straightforward.
DNS stands for Domain Name System. It is a system that translates domain names into Internet Protocol (IP) addresses, making it possible for the user to access a website without memorizing the IP address. If the browser requests a domain that’s managed by a Content Delivery Network (CDN), the DNS server will determine the best edge servers to handle that request based on the IP address.
CDN servers are the intermediary servers that exist within a Content Delivery Network. They are responsible for storing and delivering cached content and decreasing the distance between the content and the end user.