Scalability and performance considerations

Your first 100 users are easy. Your first million? That's when things break. Scalability means growing without falling apart. It's the difference between a food truck that serves 50 people and McDonald's serving millions daily.

Vertical scaling means upgrading one machine: more CPU, more memory, more storage. It works until you hit a ceiling. No matter how big the server, it can only handle so much. Horizontal scaling means adding more machines. Each takes a share of the load. Need more capacity? Add more servers. Netflix uses horizontal scaling. When millions stream at once, they don't use one supercomputer. They use thousands of regular servers working together. Each server handles some users. More users? Add more servers. This approach has no real limit. The system grows as the audience grows.