A friend was talking over dinner about when he was asked, during an interview, what happens when you type in a URL into an address bar in a browser. Lots of stuff happens!

I’m just going to start listing stuff. It’s practically impossible for me to get everything, so I’ll just do a brain dump:

• A DNS request over UDP to get an IP address
• A TCP connection gets established (SYNs and ACKs!)
• A GET request is created by the browser and sent over that connection
• Tons of different things can happen after that, including proxying, database operations, cache reads, whatever.
• The browser might get a response back
• HTML gets parsed and a DOM tree gets generated
• External resources get fetched, scripts run
• Google analytics stuff gets injected so The Man can track you

That’s pretty complicated stuff so far, but I haven’t even mentioned stuff like…

• TCP retries
• Anycast DNS (which is really cool!)
• IP transit routing
• kernel queues and buffers
• load balancing
• SO MUCH MORE.

When I was younger, the Internet was magical. When I installed my first web server in 4th grade or so, it got less magical. You know what the weird thing is? Now that I know more about what happens, it seems so magical again!