Someone else's computer

The cloud is a real, physical thing

A server is just a computer that runs programs for other computers. It has the same parts as your laptop: processors (CPUs), working memory (RAM), and disk storage. The difference is the job. Your laptop serves you. A server serves requests that arrive over a network, like loading a web page or saving a file.

You already know Docker, so you have run a web app on your own machine. To let the whole internet use that app, the container needs to run on a computer that is always on, always connected, and reachable at a stable address. That computer is a server, and it lives in a data center: a warehouse full of server racks with industrial power, cooling, and very fast internet.

The cloud means renting slices of those computers by the hour instead of buying your own. AWS (Amazon Web Services) is the biggest company that rents them.

What "renting" buys you

When you rent a server from AWS you get a slice of a machine in one of their data centers. You choose the size (how many vCPUs, how much RAM), AWS gives you an address, and you pay per hour or per second only while it runs.

A vCPU is a virtual CPU: one scheduled share of a physical processor core. The v matters. AWS splits one huge physical machine into many isolated virtual ones, which is how they can rent you a slice as small as 2 vCPUs. We will look at how that works in unit 3.

The key mental model for this whole course: every AWS service is a rented computer, a rented disk, or a rented network, with staff and software you did not have to hire or write.