1 min lesson
Capacity planning: have the numbers ready
Name the key items in "Capacity planning: have the numbers ready", then explain why each one matters.
Step 1 of 2
Capacity planning: have the numbers readywhat an EM is expected to quantify
An interviewer will probe whether you operate from data or hand-waving. Come with the three numbers that define this system's capacity and know where the bottleneck moves when load grows.
- Peak event rate - events/sec at the spikiest minute of the day, not the daily average. Size for the spike.
- p99 delivery latency target - the SLI you commit to; e.g. 99% of events delivered within N seconds of ingestion.
- The current bottleneck - broker throughput, consumer concurrency or the downstream endpoint. Name it, because that's where the next dollar of capacity goes.
Interview move
When asked to scale the system, resist adding workers first. Say: "Before I scale consumers, I want to know the bottleneck - if it's the downstream endpoint, more workers just deepen the backlog and worsen p99." Diagnosing before throwing capacity at it is exactly the player-coach instinct Cursor screens for and it separates you from candidates who reach for autoscaling as a reflex.