It Took Me Years Until I Understood Web Servers—You Can Do It In 10 Minutes

Web Servers are surprisingly simple.

A Web Server is a program that takes in a string and returns a string. The incoming and the outgoing string both adhere to rules: They follow a protocol. The protocol defines how the Web Server has to react to the incoming string. The protocol Web Servers follow is called HTTP.

A Web Server is a program that reads HTTP requests and returns HTTP responses. There are a number of requests (e.g. GET, POST, PUT, DELETE), as well as possible responses (e.g. 200 Ok, 301 Moved permanently, 404 Not found). Those HTTP requests and responses get transmitted by another protocol, TCP.

A Web Server is a program that typically runs on a machine somewhere on the World Wide Web. (And yes, this machine is called Server, too.) The World Wide Web is not the same as the Internet—it’s an application that runs on top of it. This machine has a lot of ports (65535, to be exact), and if it has a Web Server on it, at least one of these ports is open: Port 80.

You know what? We can write a HTTP request by hand. Launch a terminal and type:

> curl --verbose telnet://google.com:80 (Enter)
* Host google.com:80 was resolved (... rest of telnet answer)
GET / HTTP/1.1
Host: google.com (Hit Enter twice)

HTTP/1.1 301 Moved Permanently
(... rest of HTTP response)

In case it took under five minutes to read this once, you can read it again.