What is a server, really? A computer that waits for questions

A server isn't a special kind of machine. It's an ordinary computer running a program that waits for someone to ask for something, then answers. Your browser is the client: it sends a request, the server sends back a response.

Follow one request from address bar to finished page, run a real web server in ten lines of Python, and overload a simulated server until it starts refusing people, then fix it with a second server and a load balancer. Along the way: why servers live in data centres, and what "the cloud" really means: renting someone else's computers.