Where does content distribution network come into picture for youtube

Question

I have vaguely heard of CDNs (Content Distribution Network) and I suppose they come into picture in context of multimedia(audio/video) online sites like youtube. My question is what really are these CDNs?. Do they just mean that data is replicated at many nodes, so a user request is catered from the node nearest to him/her or is most accessible? In such case, how are they different from banking infrastructure where sensitive data is replicated at many places so that if a node crashes, we don't lose the critical data.

Thanks,

Answer 1

a CDN is just a simple network of computers distributed all around the world delivering content like images when quired by a client. They often provide from the best available network considering place and availability. They reduce the load on the main server to let the server query the database fast enough to load the site faster.

Imagine that: Your site is hosted on a shared hosting like GoDaddy. You use Wordpress for your blog. It takes time to query the database every time a person comes on your website. You setup a CDN like Amazon S3. Your photos and videos get transfered there. So when someone comes on your website now, the page will be made by getting the text and all database stuff from your godaddy hosting and all the photos and videos and also CSS from your amazon hosting.

That makes your site load much faster.

The difference is a CDN cannot dynamically make pages on the go. So you cannot use a page which is build in PHP or any other language. However you can use pages made in HTML.