System Design for Working Engineers, Not Interview Prep

Originally published at malaymehta.com The Interview Trap If you look at most system design tutorials, you get an extreme use case. Design Twitter. Design YouTube. Scale it to a billion users. Draw boxes on a whiteboard for 45 minutes. Do you think your app will be used by a billion users on day one? The answer is almost always no. But the tutorials don't teach you what to do when you have 500 users, unclear requirements, a team of four, and a quarter to ship something that works. Real system design is nothing like a whiteboard interview. You don't get clean requirements, you don't design from scratch, and nobody asks you to handle a billion requests per second on day one. Real System Design Starts with Questions, Not Diagrams The very first thing that matters in system design is something most tutorials skip entirely: unclear and chaotic requirements. In the real world, requirements don't come as a clean problem statement. They come from non-technical business teams, and you need to navigate through cross-questions to get all the clarity you need. Ask as many questions as possible. Understand your functional and non-functional requirements. Which features need to be synchronous and which can be async? What are the read and write load patterns? What is the maximum and average number of concurrent users right now? What does authentication look like? Do you need role-based access control? These questions drive your choices. You don't always need an axe where a knife will do. Being minimalist with a reasonable growth prediction and a 3, 6, 9 month plan will take you in the right direction. There will be things the situation demands immediately but would take more time than expected. Taking a predictable hit now and fixing it at the right future time without missing that balance is truly important. Weighing what will be expensive to change later, in terms of dollar cost or human effort, is how real architectural decisions get made. Pushing Back on Bad Requirements Many