A content delivery network (CDN) is a globally distributed system of servers that caches and delivers web content from locations close to end users, reducing latency and improving performance. CDNs provide both speed and high availability by serving cached content from regional nodes rather than routing every request back to a central origin server.
Content Delivery Networks
It's amazing: we can communicate across this planet, but there still is a slight delay — a delay that may or may not be a big deal. One of the ways that we can counteract that is a content delivery network, or CDN.
Let's develop a little scenario here. I'm up here in the Pacific Northwest in the United States of America, and there are some data centers around here where I could actually host web services. So let's say I'm hosting web services here. The farthest away that you can get from me would be down in South Africa, so let's say we have a user down there.
Now, it is amazing how fast communication can happen and how good a service they can get down there. But there is a delay; this is not without a delay. There are some problems that can occur when you have long distances like this. This is a good case where maybe a content delivery network would work.
So what is a CDN, or a content delivery network? First of all, it's a network. A network of what? It's a network of machines — we see machines all around the world here. And what do these machines do? They deliver content. Content delivery network. There it is.
What I would do with my services over here is subscribe to a CDN. I'd subscribe to the CDN, and then all of these servers would be working for me.
Let's give an example of this user down here in South Africa. They have a CDN location near them. What happens is, when they do a DNS resolution for my servers up here, something intercepts that and says, "Yeah, you want to actually go to this server down here." So this user is going to make a connection into this server near South Africa.
They request certain information from my website, and this may or may not be prepopulated on here. So now it goes and grabs a copy of it, and downloads it, and caches it. There might be a little delay the first time a user accesses this information, but once they access it, any other users that access this now have a fast connection, and it's really close to them, so they get a much faster connection.
As I hinted towards, you can either prepopulate this stuff — force it, and say, "Yeah, prepopulate all of these machines so it's already there" — or, when they retrieve it the first time, then it will just make a cache of that, and any other users then will access that cache.
Now, for a site, some of the information is dynamic, and it'll always go back to the main server for that dynamic information, but everything else that can be cached, it'll access from the local server. As an example, I worked with a SaaS company, and 97% of our content could be downloaded onto these cache systems. So 97% of the stuff could operate at a much faster speed through this content delivery network.
These CDNs really provide high availability and performance: performance as I mentioned before, and then high availability, because now you have this whole network of cached content that could be accessed anywhere in the world.
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