How a CDN Works: Understand How a CDN Speeds up Your Website


By Ann Oliver

With the tremendous growth of internet reach, more people today stay connected online for seamless communication, entertainment, knowledge sharing, accessing the global workforce, and more! This exponentially increasing internet user facilitates businesses by offering the opportunity to broaden their virtual reach through websites. 

But, to sustain the site’s optimal status and stand out from the pack in this competitive digital marketplace, offering seamless browsing is vital. Here comes the significance of incorporating a CDN with your site. 

If you wonder about this service and how a CDN works, I have come with everything essential. 

What is a CDN

A CDN is a group of web servers with dedicated PoPs (Points of Presence) positioned worldwide. After getting integrated with your site, it ensures website availability, optimises asset delivery, and offloads traffic from the hosting server. Thus it offers an impeccable user experience. 

Whether you run a B2B or B2C site with extensive visitors outside the origin server location, you can reap the advantages of CDNs (Content Delivery Networks) and speed up your site. 

Edge Servers

These are separate computers installed at the PoPs of a network and act as the bridge between two networks.

 A CDN edge server:

  • Caches your site content, receiving it from the host server. 
  • Offers smooth and optimised delivery
  • Facilitates traffic management
  • Limits latency

Types of CDN

CDNs are of two kinds:

  • Push CDN: Push CDNs work similarly to a host server. They already store and distribute cached data at the edge servers collecting it from the origin server, irrespective of an access request. With a push CDN, you get the flexibility to determine which content to ‘push’ to the CDN, when to update or expire it. 
  • Pull CDN: In a pull CDN, the CDN doesn’t cache web pages or data in advance. Once it gets a request, it ‘pulls’ the original file from the host server. It then caches it for further requests. You only have to put the pages in the hosting server and rewrite the URL pointing to the CDN. 

Origin Server

It is essentially the server that hosts your site and stores associated data and content. Unless you add a CDN to your site, visitors’ requests are responded to and served by the origin server. 

How a CDN Works

A CDN aims to cache files to transfer them to the users from the servers proximal to them. 

Let’s get an in-depth overview of how a CDN works:

  • Let’s assume someone has requested a static resource (images,videos, Javascript, HTML, etc.) of your website.
  • If you have already incorporated a CDN, the CDN will retrieve the original content or page from the host server.
  • The edge server (caching server) most proximate to that visitor will copy and forward it.
  • If the edge server gets further requests from the same user to access the same asset, it sends the cached content.
  • If a CDN server accepts a request for the first time, it repeats the preceding steps and transfers the content after caching. 

Let’s understand the process with a simple example:

  • Let’s imagine a visitor from the USA has made an access request for content or page of your UK-hosted site. 
  • If you serve the visitor with your origin server, it will produce a delay of a few milliseconds to load a web page, as the request will require to travel over the Atlantic!
  • CDNs aim to decrease this delay (latency) by storing your site data in various locations.
  • For instance, when you add a CDN to your site and transfer the page to that USA user from the PoP placed in the USA closest to him/her, the page will load faster, boosting performance. 

Why Employing a CDN

The reasons to implement a CDN are many and not limited to:

Lowered Bandwidth Usage and Cost

Through caching static resources (sometimes both static and dynamic) and delivering them to the users, CDNs ensure fewer data transfers from the origin server. The fewer data an origin server has to handle, the less bandwidth will be consumed, which, in return, will cut bandwidth expenses. 

CDN Ensures Redundancy and Content availability

Your site may slow down or even crash due to heavy traffic or hardware malfunctions. CDNs can manage heavy traffic, distribute content across the caching servers, and keep your site available. 

Top-notch Security

All CDNs offer some basic security measures to safeguard sites from cyber attacks. The providers ensure top-notch protection against DDoS attacks, abusive bots, data loss, and suspicious IPs with WAF (Web Application Firewall), SSL certificate, and TLS encryption

Boosted Speed and Performance

Latency, the delay a server makes to respond to a user’s request, is the leading reason for a higher bounce rate in websites. CDNs ensure well-managed load distribution among CDN servers and send data from the PoP positioned near to end-users. 

The less distance a request has to cover, the more increased the loading speed is. It boosts your site performance, offers a high-performance network, and your users can enjoy a better browsing experience resulting in lowered bounce rate.

Example of a Lighthouse report on a website’s performance and accessibility

What to Look for in a CDN

Are you considering adding a CDN service to your site, but wondering what criteria you should focus on? Evaluate the following factors before choosing one:

  • Pull and Push Functionality: If your site experiences heavy traffic, go for a pull CDN. For a website with less traffic, a push CDN works great.
  • Look for logging Features: Evaluate if the CDN you consider employing is rich in logging features for effortless storing, searching, monitoring, and analysing logging data. 
  • Customisation: You should always go with the CDN that enables web owners to customise the service according to their requirements. Look for a provider that features customisation for SEO, security certificate, delivery, etc. 
  • DDoS Attack Mitigation: Another vital factor you should focus on while buying a CDN service is whether it comes with DDoS (distributed denial-of-service) attack mitigation to shield your optimal traffic from malicious attempts.
  • HTTP/2 Support: Evaluate if the CDN you have selected comes with HTTP/2 support that can make your site perform excellently and offer your users a more seamless web browsing experience than HTTP/1.1.
  • Real-time Analytics: It is another significant factor in a CDN you cannot overlook. A service that offers real-time analytics enables you to monitor and analyse web traffic, cache, and cyber threats keeping an expert eye on the host server’s overall state.