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mediumQA Engineer interview question

You are asked to performance test a new API before a big launch. How do you plan and run it?

What the interviewer wants to hear

  • Agree goals: expected and peak traffic, percentile response-time targets, error budget
  • Build a realistic workload model from analytics: endpoint mix, data, think time
  • Use a production-like environment and test data, and monitor the servers
  • Run several test types: baseline, load, stress, spike and soak
  • Analyse p95/p99, throughput, errors and resource use; find bottlenecks and retest

Model answer

I start by agreeing measurable goals with product and engineering, for example 1,500 requests per second at peak with p95 under 400 ms and errors under 0.5%. Then I build a workload model from analytics or business forecasts: which endpoints are called, in what mix, with what data and pauses. I script it in k6 or JMeter and run it against a production-like environment with realistic data volumes, while watching CPU, memory, database and queue metrics. I run a baseline first, then a load test at expected peak, a stress test to find the breaking point, a spike test for launch bursts and a soak test for leaks. I report percentiles rather than averages, and where it fails I work with developers to find the bottleneck and rerun. Thresholds in CI catch regressions later.

Can you answer it under time pressure?

Take a timed medium round and get scored on every answer.

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