What Is a CDN?


A content delivery/distribution network (CDN) is a geographically distributed cluster of nodes that operate together to serve web content in agility and speed. This web content can be static pages like HTML, CSS, JavaScript files, images, fonts, audio files, and videos.

The CDN has a significant role in the success of a business site. Today, the majority of internet traffic traverses through CDNs. From an end user’s perspective, every individual interacts with CDNs in one form or another on a daily basis. For example, CDN is used to deliver content to you when:

  • You read articles on an online news site.
  • You shop on an e-commerce site.
  • You use social media apps and are served targeted ads.
  • You watch your favorite YouTube videos.

A securely configured CDN can help protect your sites against malicious attacks such as distributed denial-of-service (DDOS) attacks.


Traditionally, internet traffic is handled between a client and server through requests and responses. When a user visits a website, a request is sent from the client (usually a web browser from the user’s computer) to the server (host machine serving the website). The server responds with the requested HTML page, along with style sheets and associated files, such as images or JavaScript files based on the page requested. The same request and response cycle gets repeated again and again whenever the same page is requested by the client.

However, as internet usage and the site’s popularity increase, the traffic increases, which often leads to a noticeable drop in server performance. This is because the server capacity can’t handle so many requests from multiple clients. Thanks to this traditional (and somewhat outdated) client-server interaction model, users begin experiencing latency issues and poor user experience.

CDN has emerged as a solution to all these issues. By distributing servers across multiple locations and caching static web content during the first client request to the server, further requests can be served at a faster rate by avoiding the client-to-server round trip.

As you can see, the most common use of CDN is to increase loading speeds and a website’s responsiveness. This also helps reduce bandwidth cost and consumption. This article will cover more details on how CDNs work and provide various use case examples to show you how this innovative solution can work for you.

How Does a CDN Work?

To serve web content from the origin server quickly and reduce both the timeframe and travel distance between the users of a site and the corresponding web server, a CDN stores the web content of the origin server in its cache. This cache is stored in multiple geographical locations based on the target user base of the site.

In general, CDNs depend on data centers at multiple strategic spots in the world. For example, if your business site has a prominent user base originating from the US, UK, and India, you should have a CDN presence in all these three locations. These locations are called points of presence (PoPs) or Edge locations. Each PoP has many caching machines responsible for caching and delivering the web content to its users.

For example, when a user in India requests your US-hosted website, the request is handled through a CDN PoP in India for a quick turnaround time. This is a win-win situation for both the user (faster page loads and improved user experience) and the organization that owns the website (cost savings, improved website experience, and happy customers).

Example of a CDN

The following diagram illustrates how a CDN works in a hypothetical business site setup:

Now that you’ve understood the role of CDN and how it works, the following paragraphs will explain how caching in CDN works on a conceptual level.

When a user from the UK requests the site, a cache lookup occurs for the server’s content. Since this is the first time the request is coming from the client, a cache hit does not occur — in other words, it’s a cache miss scenario. So, the request is forwarded to the US origin server. The cacheable web content then gets saved in the CDN cache, usually enabled by clicking on a check box in the CDN provider’s console interface. The response then gets served to the user.

The next time a similar request originates from the client in the UK, a cache hit occurs in the CDN node, and the request gets served from the local UK-based CDN cache nodes. The origin server will not receive the request from the client to serve the cacheable content, thus reducing the data transmission time and network traffic costs. Also, due to the faster response, the user has a great experience with the website. The same scenario is true for users of the site from India.

CDN Use Cases

There are cases where CDNs make website content stable and traffic more manageable. Some examples of use cases for CDNs are highlighted below.

E-Commerce Sites

In the case of e-commerce sites where thousands of products are sold daily across the world, the site’s coverage must reach users in multiple geographical locations with both speed and agility. CDNs are great at reducing the user request distance between the client and origin server and offloading the server’s load, especially during big sales.

Government Sites

In the case of government sites, a lot of public-facing static content is available for access to the general public. For densely populated countries like China and India, many government sites carry information to the public that needs to be readily accessible. The CDN has a vital role in enhancing the user experience here.

SaaS Platforms

Many SaaS platforms use CDNs to handle large data as quickly, efficiently, and reliably as possible. One such SaaS platform is Salesforce. Salesforce uses CDN to enhance its customer’s digital experience by serving the static data and files of its Salesforce platform at a faster rate.

Real-World CDN

As you can see, CDN is used by multiple organizations around the world. This section provides examples of real-world CDN applications in different companies.

Chartboost is a global ad platform that helps gaming companies make money from mobile games based on their users. This platform depends on StackPath’s global CDN infrastructure to deliver gaming ads quickly, reliably, and at appropriate intervals to over 900 million monthly users. These ads are distributed across over 300,000 mobile games installed by users spread across multiple geographical locations. You can find out more in this case study.

Thanks to CDN technology, the podcast S-Town saw a record-breaking 10 million downloads in just four days. The producers knew their podcast would demand a lot of subscribers from the online community and needed a reliable CDN partner to host and stream the content in a reliable, low-latency, and continuous manner. You can learn more about how that was made possible thanks to Highwinds CDN.

Key Takeaways

  • A content delivery/distribution network (CDN) is a cluster of nodes across multiple locations that cache static web content such as HTML, JavaScript files, images, and more.
  • CDNs are useful for speeding up server performance during high web traffic, meaning the website doesn’t slow down during peak periods.
  • CDNs add significant value to business websites by increasing loading speeds and responsiveness.
  • To use a CDN, you need data centers in every location where you have a prominent user base (points of presence or edge locations).
  • CDNs provide benefits to a wide range of industries, including ecommerce, SaaS platforms, and government bodies.

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