CDN

Content Delivery Network

A set of servers that are dispersed across the world to deliver assets to web users more quickly.

The web is really fast.

Like...really fast. Even if you understand how The Internet really works, it's still pretty unbelievable that the modern internet even works - and is as fast as it is across the entire world.

One of the the pieces of The Internet Puzzle that makes a site fast across the world is a CDN.

The problem#

A website will have a central server where cute-puppy-image.png exists. That website's server may live in San Francisco, California, USA.

If I live in Los Angeles, California, I can get to that image pretty quickly. That image will travel to me at the speed of light so it will be delivred to me nearly instantly (or at least so fast that a human won't care).

But, if you live in Berlin, Germany, you still have to ask a server in San Francisco, California for cute-puppy-image.png. You live far enough away that, even at the speed of light, you may notice that this image comes to you with a bit of a delay.

The solution#

Here is where the CDN comes into play.

The first time that someone in Germany asks for cute-puppy-image.png, the CDN will make its own copy of this image, save it in a server in Germany, and keep it around for later. This process is called caching.

Now, the next time someone in Germany asks for cute-puppy-image.png, the CDN will say "Hey, look, I have a version of that already here in Germany! I'll just give it to them from here since I'm only down the street from their house!"

Check that out. Now, you, in Germany, didn't have to visit California to get your cute puppy image. Instead, you got it from somewhere way closer to you. That image will now load way quicker for you so you will have a better web experience.