For example, lets say your website was hosted on a server in Atlanta GA. Then, whenever your customer requested your website that did not use a CDN, the request would always come to your server in Atlanta. Local customers may have a decent experience because they are local, but requests from customers on the west coast would have to travel the span of the US. Even worse for global customers.
With a CDN, the CDN provider will have servers in many places around the world. They may have a few servers on the west coast, some in the midwest, some in the east coast, and some in Europe, Asia, Africa, and Australia for example. When your users request your website that uses a CDN, their request only has to go to that local server, thus making the experience a lot faster.
IMPROVED SEARCH ENGINE (SEO) RANKINGS
A faster performing website is one of the signals search engines such as Google use to rank your website. A CDN will help your images load faster, and your overall website responses will be generally quicker.
If you are serving requests for a large number of customers (hopefully your website just went viral), then a CDN will also help cushion the amount of work your web server has to do, thus maintaining fast website performance.
FASTER EXPERIENCE - WHY YOUR SITE SPEED IS CRITICAL
Users have very low tolerance for slow loading websites. If you page does not load within 2 seconds, most users will leave your website and go to a competitor. This is the number one factor your customers use to judge your website. First impressions matter! Thus, you want to have fast loading pages, optimized images, and definitely no Flash.
A 1 second delay in loading will cause 7% of users to bail.
A CDN will help with this experience by caching your content on a server nearer to the user. Some CDN’s will even optimize your images for you.
A better user experience will result in customers wanting to stay on your website longer. This means you have more chances to sell your customer on your product or service, and for you customer to ultimately sign up with what you are selling.
Because the CDN servers are handling the bulk of requests coming to your website, you get some protection from a DDOS (Distributed Denial of Service). A DDOS can happen in two ways. The first is malicious, where a bad actor uses a network of computers (bots) to make thousands/millions of requests to your website with the intention of bringing your site down and impacting real customers. The second way a DDOS can happen is if your website or one of your pages went viral and millions of legitimate customers try to access your website. Ever been on SharkTank?
A CDN will generally absorb a lot of this traffic, thus allowing you to serve more customers, and making it harder for an influx of users to bring down your site.
WHICH CDN PROVIDER SHOULD YOU USE?
There are many CDN providers out there such as Akamai, Amazon CloudFront, Verizon Edgecast, Fastly, MaxCDN, and the list can go on.