System design interviews are tough. Not because the questions are impossible - but because they’re open-ended, and most people don’t know where to start.

After years of building distributed systems in FinTech, I’ve been on both sides of the table. I know what interviewers are actually looking for, and it’s not buzzwords. It’s trade-offs, real-world thinking, and knowing why something works, not just that it works.

So I’m putting together this series — practical write-ups on the topics that come up again and again. No fluff, just the stuff that matters.

Who is this for? #

Doesn’t matter if you’re just starting out or have years of experience. Each article explains the concept clearly first, then goes deeper into the trade-offs and implementation details. Take what’s useful for your level.

What we’ll cover #

Here’s the planned lineup (I’ll link each as it’s published):

How to use this series #

System design interviews are conversations, not exams. The best answers are structured, trade-off-aware, and show that you’ve actually built (or broken) real systems. Each article follows the same format:

1. The core concept — what it is and why it matters
2. The interview question — typical ways interviewers phrase it
3. The trade-offs — what you gain and what you give up
4. Implementation patterns — practical approaches with examples
5. What a strong answer looks like — tips on how to frame your response

Let’s start with one of the most underestimated topics in distributed systems: Idempotency.

➡️ Part 1: Idempotency — What It Is and How to Handle It