War Rooms

The vocabulary lesson — every system design answer is built from these six moves.

The 'hello world' of system design — every concept in miniature.

Small surface, deep trade-offs — the classic 'do you actually understand distributed state?' question.

The fanout question — push vs pull, and the celebrity who breaks both.

The canonical queue question — decoupling, retries, and idempotency in one design.

WhatsApp-style messaging — the case that teaches you stateful servers.

Two systems in a trench coat — a write-heavy pipeline and a read-heavy edge, joined by a CDN.

Dynamo in five moves — the most conceptual case you'll ever be asked.