What is a Content Delivery Network or CDN?

Imagine you're building the next big video streaming service - something like YouTube or Netflix. You've got all these amazing videos that people want to watch, and you're storing them safely in a cloud storage service like Amazon S3. Sounds great so far, right?

But here's where things get tricky. Let's say you have a user in India who wants to watch their favorite cat video. If your video is stored in a data center in the US, that video has to travel halfway across the world before it reaches their screen.

When videos have to travel such long distances, a few annoying things might happen. First, there's the waiting. You click play, and the video takes forever to start. Then comes the dreaded buffering - you know, that spinning circle that shows up right at the most exciting part of the video? This happens because the video data has to hop through multiple networks and cross oceans before reaching your device.

This is where CDNs (Content Delivery Networks) come to the rescue. Instead of having just one central storage location, CDNs maintain multiple copies of your content in different locations called "edge servers".

Now, when our friend in India wants to watch that cat video, they don't have to reach all the way to the US. Instead, they get the video from a nearby CDN server in Asia, maybe from Singapore or Bangalore.

CDNs don't store every single video at every location - that would be expensive and inefficient. Instead, they learn what content is popular in different regions and store it accordingly. If a particular video becomes viral in India, the CDN automatically ensures that multiple copies are available in servers across India.