System Design Card 426 — Rate Limiting / Breakdown
Concern
Rate limiting protects multi-tenant fairness, abuse resilience, and downstream stability. An API gateway or notification ingress often needs both per-user and per-tenant controls.
What Breakdown means for this concern
In BASIC, the Breakdown step is where you clarify the product goal, workload shape, and non-functional requirement that will dominate the design. For Rate Limiting, that means the candidate should make this concern visible at the right moment instead of bolting it on at the end.
Design move
A good move is to split the problem before trying to solve it. Tie the concern back to the user flow, the workload, and the dominant trade-off. That keeps the design grounded and makes it easier for the interviewer to follow why a cache, queue, replica, partition, or rate limiter is actually necessary.
Common miss
The miss is discussing scale without discussing protection against pathological clients. BASIC helps because the staged flow keeps this concern proportional to the prompt and connected to the rest of the architecture.
BASIC prompt
“When I reach the Breakdown stage, how does Rate Limiting change the architecture, the trade-offs, or the review checklist?”