WhatsApp served 900 million users with just 50 engineers. Read that again. Most companies would throw thousands of developers at that problem. WhatsApp did it with a team that could fit in a small office. This is not luck. It is the result of deliberate technical choices that most developers overlook. Erlang instead of Java. FreeBSD instead of Linux. A focus on simplicity over features. This post breaks down exactly how they did it. No fluff. Just the architecture decisions that made massive sca...