Content delivery network (CDN) - definition & overview

A CDN is one of the most important tools for optimizing the performance of heavily-trafficked websites and applications that are deployed in cloud environments. A CDN is a network of proxy servers and supporting data centers that are configured to service requests for a single website or web application. CDNs use geographical proximity as the main criteria for determining which server will fulfill a given request. A CDN shortens the physical distance between clients and the servers fulfilling their requests, reducing overall latency and achieving superior demand management to enhance the customer experience.

Each website on the internet is hosted on a web server, a piece of software or hardware that is configured to receive and satisfy requests from the web. Web servers communicate with client browsers using the hypertext transfer protocol (HTTP) language and typically transmit web pages in the form of HTML and CSS files, along with audio, video, images and other forms of content. The most common web servers are Apache Web Server, Microsoft's Internet Information Server (IIS) and the NGINX open-source web server.

Web servers face limitations when it comes to simultaneously serving large amounts of requests. Most web servers can only maintain 5,000 or 10,000 connections at a given time, meaning that periods of high demand can result in lost packets, unfulfilled requests, and server overload. In addition, large geographical separation between the web server and the client results in greater packet latency, which can result in lost packets and poor website performance.

To overcome these challenges, many of the most frequently visited websites on the internet have deployed a CDN to help reduce latency and deliver consistent performance for users around the world. For the world's largest and most popular websites, maintaining a robust CDN that can rapidly deliver content to users is key to business success.

For example, in organizations that create and deliver online gaming experiences, latency can result in game-breaking bugs and errors that frustrate the end user. The average session time by a user can be correlated with the network quality. A user with low latency is much more likely to play for longer than a user experiencing high latency or packet loss.

Enterprise IT organizations may establish their own CDN in a set of globally distributed data centers, but there are also CDN vendors who provide the servers and infrastructure that organizations may leverage to deliver their content to users more efficiently.

In the typical business model, content owners contract with CDN operators who assist with worldwide content delivery and CDN operators contract with global internet service providers, carriers, network owners and other entities to host servers that fulfill requests for their customer's content.

The key functional aspect of CDN is that when a user requests content from a given website, the request is routed to the nearest server in the CDN instead of to the origin server. CDN stores cached static content from your website on edge servers - servers that exist at the edge of the network, most proximal to the user. A CDN can also be used to serve dynamic content from your website - content that is updated frequently and therefore can't be cached. In a third use case, CDN can even be implemented to support video streaming services.

The goal of implementing a CDN is to reduce latency by delivering content to users from a server that is geographically closer to the origin of the request. The benefits of CDN fall into four general categories:

Enhance website or application performance

Website performance has a positive effect on customer experience and satisfaction and may influence other factors like search engine rankings and revenue generation. A CDN drives down latency time and makes it easier for users to access the services they desire on your website. Reducing latency has been shown to reduce bounce rate, reduce instances of abandoned shopping carts and encourage users to spend more time on your website or application.

Increase system reliability and reduce downtime

With a CDN implemented, requests are always routed to the nearest edge server - even when you're experiencing a partial outage. Redundancy is built into the CDN network, ensuring that there is always a server with sufficient capacity available to fulfill a request while optimizing service users as quickly and efficiently as possible.

Security and threat mitigation

Updates to your website are deployed on your company's origin server before being reflected on edge servers of the CDN where they may be requested by users. Edge servers act as a barrier between the origin server and any potential cyber-attacks, making it that much more difficult for cyber attackers to directly target your servers. CDN platforms can be implemented with SSL certificates to encrypt CDN traffic. CDN platforms support a high volume of connections, making them naturally resistant to DoS and DDoS cyber attacks.

Sumo Logic builds applications to support CDN implementations with two industry-leading vendors: Fastly and Akamai CDN.

Fastly enhances web and mobile delivery with a sophisticated global system for accelerating user access to dynamically changing assets and caching static content. The Akamai CDN network includes 216,000 servers deployed in 1,500 networks in over 120 countries around the world.

With Sumo Logic, users of these CDN platforms can streamline the analysis of CDN log files to better understand the relationship between website performance, latency and user behavior. Sumo Logic's real-time analytics capabilities empower IT organizations to monitor website and application performance life and react quickly to operational or performance issues before they negatively impact customer experience and revenue.