One box runs everything

One server runs everything

Every system you have heard of, Google, Netflix, WhatsApp, started as one program on one computer. This course grows that one computer into a planet-scale system, one problem at a time.

You already hold the prerequisites. From How the Internet Works you know a browser sends an HTTP request and gets back a response. From backend basics you know a server is a program listening on a port. From SQL you know a database stores rows in tables.

Our starting point, and the anchor picture for the whole course, is the simplest real architecture:

• One machine in a data center (engineers call it a box)
• The app process: your backend code, running on that box
• The database: running on the same box

Plenty of profitable products run exactly this. Never add complexity before the simple version breaks.

The life of one request

When a user taps Load feed:

1. The browser sends GET /feed across the internet to your box (DNS and TCP, exactly as in How the Internet Works)
2. The app process runs your handler code
3. The handler queries the database: SELECT * FROM posts WHERE ...
4. The database reads rows from disk and returns them
5. The app turns rows into JSON and responds

Total time is a few milliseconds of app code plus tens of milliseconds of database and network time. One box can do this thousands of times a minute without strain.

How much traffic is that in real units? The number system designers care about is requests per second, written RPS. Let us compute it.