The 14 system design concepts that cover ~80% of interviews

You don't need a 500-page distributed-systems textbook to pass a system design interview. You need to be fluent in about 14 building blocks — and, more importantly, in the trade-off each one forces you to make out loud. Interviewers aren't grading whether you've memorized Kafka internals; they're grading whether you can reason about trade-offs under ambiguity.

Here are the 14, each with the one trade-off you'll actually be asked to defend.

The 14 concepts

1. Horizontal vs Vertical Scaling — Vertical = a bigger box (simple, hard ceiling). Horizontal = more boxes (elastic, but now you have distributed-systems problems). Say which and why.

2. Load Balancing — Spreads traffic across servers. The interview question is the algorithm (round-robin vs least-connections) and what happens to sticky sessions when a node dies.