How Does a CDN Work?


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The most significant factor driving the growth of the content delivery network market is end user interaction with online content.

This interaction between a user and online content is far more complex today than it was a few years ago. 

Today’s users are much more likely to be streaming a longer video from a mobile phone or accessing a SaaS portal when working from home. These are far more complex experiences that did not exist five or so years ago. Given the expected growth of the CDN market in the coming years, this guide will define exactly what a content delivery network is and how a CDN works.

What is a Content Delivery Network? 

A content delivery network, also called a CDN,  improves the website performance as well as its security and reliability. It does this by bringing web content closer to the geographic location of users. A CDN is essentially a geographically distributed network of servers and their data centers that help in web content distribution to users with minimal delay. 

CDNs are especially useful for businesses which attract a large amount of web traffic. Video streaming platforms like Netflix, social media giants like Facebook and e-commerce giant Amazon all rely on CDNs to deliver their content to end users.

How CDNs Works

As mentioned above, a CDN works by bringing content closer to the geographic location of the end users. It does this through strategically located data centers known as Points of Presence (PoPs) . These are data centers situated around the world, and within each PoP are thousands of caching servers. Both the PoPs and servers help improve connectivity and accelerate the speed at which content is delivered to the end user.

How Does a CDN Work?

To understand in detail how a CDN works, it helps to look at what happens in the absence of one.

Consider a user in Singapore trying to load the webpage of a business, say a streaming services provider. The user sends a request to the business’ web server to retrieve all the page’s components. The page could include text, images, HTML and dynamic content. The origin server could be located anywhere in the world. Let’s say it is in North America. Now this origin server which stores all the content on the web page has to deliver it to the user’s browser all the way across the globe. This simple fact of geographic distance can create delays and performance issues.

When a CDN is used, the content can be stored in the local PoPs that are set up closer to the end user. These PoPs cache the files on the web page and deliver it to the end user in much less time when requested, improving page load speed. If the CDN does not have the files requested by the user, it will load from the origin as needed.

CDNs are especially useful when websites have dynamic content. For such web pages, CDNs create a “super highway” to accelerate the delivery of content across a longer distance. An individual ISP cannot provide this.

How Does CDN Caching Work? 

CDN Caching is a crucial part of what makes content delivery networks work. It is the process of storing a copy of files delivered to a user the first time and reusing those stored copies of the assets for subsequent requests instead of the original files. In a CDN, the edge servers are where the data is cached.

CDN caching works roughly as per the following steps:

  1. An end user requests for static assets on your web page for the first time
  2. The assets are retrieved from the origin server and once delivered are stored in the PoP edge caching server close to the end user.
  3. When the same user requests the same assets the next time, the requests don’t go to the origin server. Instead the requests go to the cached files from the PoP server to see if the stored assets are still available and deliver them to the user.  If they are not available or the caching server has not cached the assets yet, the request is sent to the origin server again.

Once your static assets are cached on all the CDN servers for a particular location, all subsequent website visitor requests for static assets will be delivered from these edge servers instead of the origin, thus reducing origin load and improving scalability.

Why Is It Important You Know How CDN Works?

CDNs are important for businesses that rely on distributing content to users across the globe. They comprise a network of strategically distributed CDN servers, each of which aids in content delivery.

They help optimize bandwidth and latency

The main benefits of using CDNs involve bandwidth and latency reduction. Latency refers to the time it takes for web pages to load. By moving and storing website content closer to the users, CDNs help in reducing page load times and optimization of the browsing experience.

For example, consider a cloud gaming company or a business that provides video streaming services. Their data centers could be located in New York or Los Angeles in the United States. But their end users and consumers could be located all over the world. It may still be relatively straightforward for users in Austin or Maryland to download all of their content when using their services. But what about users located miles across the globe in Australia or Japan? Without a CDN, each of these users will also have to download all the content every time and this will lead to delays and an inconsistent user experience.

At the end of the day, the geographic distance between the web server and end user makes a big difference. Using a CDN, this distance can be minimized and the user experience optimized. This has a direct impact on the business revenue as unsatisfied users and customers can be turned away to other competitors. 

They help improve website security

The distributed nature of CDNs makes it ideal for handling large amounts of web traffic such as those from DDoS attacks that could otherwise result in server failure and downtime. Techniques such as HTTP load balancing in a CDN help in preventing and detecting such DDoS threats. 

Another functionality of CDNs include the provision of fresh TLS/SSL certificates for better authentication, encryption, and integrity standards. They also improve content availability and redundancy and ensure that even if one server goes offline, others can pick up the web traffic. By the same token, CDNs can also offer Distributed Denial of Service or DDoS protection by distributing the malicious requests across the network.

They help control access to different regions

CDNs are also important for your engineering teams and website owners to manage access to your platform or services. If your business has users or consumers who are distributed across the globe, you may often have to allow access for some regions and deny access for others. 

CDNs can help your engineering teams offload web application logic to the edge servers. They can use CDNs to delegate authentication tasks to the edge, respond to requests from different regions based on request attributes and process the header and body attributes in requests and responses.

 CDNs also help in collecting logs and analyzing user-generated data. This is crucial if your business attracts a high number of website visitors and when you need to analyze the web traffic in real-time.

They allow for prefetching content for faster delivery

Another reason why CDNs are important is their ability to prefetch static website content in advance to the edge servers. Static content includes assets like images, media files and static parts of HTML, CSS or Javascript files that don’t change often. Even dynamic content, such as a WebSocket application that listens for events from a server can be addressed if there is a tight integration between the CDN.

They are a cost-effective for managing traffic

Above all, the billing model for CDNs allow you to pay according to the traffic and the amount of requests, although HTTPS requests can involve additional costs due to the extra computing resources required.

Why Use CDN?

With nearly every business today relying on digital channels to attract customers, the importance of CDN services has become undoubted. Cloud and online gaming, media and entertainment including video streaming, e-commerce and advertising are just some industries where CDN providers can help distribute content to users across different parts of the world.

That doesn’t mean CDN will be a good choice for everyone. If your business operates from a localized website and if your user-base is also concentrated around your server, CDNs may end up being overkill. In fact, in such cases, CDNs can even harm your users’ experience on your website as there will be unnecessary nodes that stand in between the server and the client.

This guide has described how a CDN works and if you are looking for a way to deliver content to your customers quickly and seamlessly, irrespective of where they are located in the world, talk to a CDN provider today.

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