What is a content delivery network (CDN)? | How do CDNs work?

Explore how a CDN delivers fast, efficient, and secure content to websites and Internet services.

What is a Content Delivery Network (CDN)?

A content delivery network (CDN) is a geographically distributed group of servers that caches content close to end users. A CDN allows the quick transfer of assets needed for loading Internet content, including HTML pages, JavaScript files, stylesheets, images, and videos. The popularity of CDN services continues to grow, and today, most web traffic is served through CDNs, including traffic from major sites like Facebook, Netflix, and Amazon.

A properly configured CDN may also help protect websites against common malicious attacks, such as Distributed Denial of Service (DDOS) attacks.

Is a CDN the same as a web host?

While a CDN does not host content and can’t replace the need for proper web hosting, it does help cache content at the network edge, which improves website performance. Many websites struggle to meet their performance needs with traditional hosting services, so they opt for CDNs.

By utilizing caching to reduce hosting bandwidth, helping to prevent interruptions in service, and improving security, CDNs are a popular choice to relieve some of the major pain points that come with traditional web hosting.

What are the benefits of using a CDN?

Although the benefits of using a CDN vary depending on the size and needs of an Internet property, the primary benefits for most users can be broken down into four different components:

Improving website load times – By distributing content closer to website visitors using a nearby CDN server (among other optimizations), visitors experience faster page loading times. As visitors are more inclined to click away from a slow-loading site, a CDN can reduce bounce rates and increase people’s time. In other words, a faster website means more visitors will stay and stick around longer.
Reducing bandwidth costs – Bandwidth consumption costs for website hosting are a primary expense for websites. Through caching and other optimizations, CDNs can reduce the data an origin server must provide, thus reducing hosting costs for website owners.
Increasing content availability and redundancy – Large traffic or hardware failures can interrupt normal website function. Thanks to their distributed nature, a CDN can handle more traffic and withstand hardware failure better than many origin servers.
Improving website security – A CDN may improve security by providing DDoS mitigation, improvements to security certificates, and other optimizations.

How does a CDN work?

A CDN is a network of servers linked to deliver content quickly, cheaply, reliably, and securely. A CDN will place servers at the exchange points between different networks to improve speed and connectivity.

These Internet exchange points (IXPs) are the primary locations where different Internet providers connect to provide each other access to traffic originating on their different networks. By connecting to these high-speed and highly interconnected locations, a CDN provider can reduce costs and transit times in high-speed data delivery.

Beyond the placement of servers in IXPs, a CDN makes several optimizations on standard client/server data transfers. CDNs place Data Centers at strategic locations across the globe, enhance security, and are designed to survive various types of failures and Internet congestion.

Latency – How does a CDN improve website load times?

When a website loads content, users drop off quickly as the site slows down. CDN services can help to reduce load times in the following ways:

The globally distributed nature of a CDN means reduced distance between users and website resources. Instead of connecting to wherever a website’s origin server may live, a CDN lets users connect to a geographically closer data center. Less travel time means faster service.
Hardware and software optimizations such as efficient load balancing and solid-state hard drives can help data reach the user faster.
CDNs can reduce the amount of data transferred by reducing file sizes using minification and file compression tactics. Smaller file sizes mean quicker load times.
CDNs can also speed up sites that use TLS/SSL certificates by optimizing connection reuse and enabling TLS false start.

Reliability and redundancy – How does a CDN keep a website always online?

Uptime is critical for anyone with Internet property to be shared on the Internet. Due to malicious attacks or a boost in popularity, hardware failures and spikes in traffic can bring down a web server and prevent users from accessing a site or service. A well-rounded CDN has several features that will minimize downtime:

Load balancing distributes network traffic evenly across several servers, making it easier to scale rapid boosts in traffic.
Intelligent failover provides uninterrupted service even if one or more CDN servers go offline due to hardware malfunction; the failover can redistribute the traffic to the other operational servers.

Data security – How does a CDN protect data?

Information security is an integral part of a CDN. A CDN can secure a site with fresh TLS/SSL certificates, ensuring a high authentication, encryption, and integrity standard. Investigate the security concerns surrounding CDNs and explore how to deliver content securely.