A structured approach to system design interviews. The difference between senior and staff-level candidates is almost entirely in how they structure their thinking.

The 5-Step Framework

Do's and Don'ts

Think out loud. Interviewers want to see your thought process, not just the answer. A great wrong answer with good reasoning beats a lucky right answer with no explanation.

Drive the conversation. Don't wait to be asked. Lead with: "I'm going to start with requirements, then estimate scale, then sketch the HLD. Does that sound good?"

Don't jump to solutions. Designing before clarifying requirements is the #1 interview mistake. You'll solve the wrong problem and waste everyone's time.

Don't say "use Kafka" without reasoning. Every technology choice needs a why. "Kafka because it handles high throughput and message replay" beats "Kafka" alone.

Acknowledge trade-offs explicitly. "We could use PostgreSQL here for strong consistency, but at 1M writes/sec we'd need heavy sharding. Cassandra trades consistency for write throughput — that's acceptable here because..."