Mid-LevelPerformance & Load Testing
How do you test API performance under different network conditions?
- network conditions
- latency
- throttling
Answer it first, then compare. Nothing here is saved or scored.
Model answer
Simulate real-world network conditions: (1) Latency injection: add 50-500ms delay to simulate mobile/satellite networks. (2) Bandwidth throttling: limit to 3G/4G speeds. (3) Packet loss: simulate unreliable connections (1-5% loss). (4) Test timeout handling: verify the application gracefully handles slow responses. (5) Test with different geographic regions (via CDN or cloud region testing). Tools: tc (Linux traffic control), Chrome DevTools throttling, k6 with custom scenarios, Toxiproxy for service-level network simulation.
What interviewers listen for
- Workload modellingYou design the load shape from product traffic, not from tool defaults.
- Percentile literacyYou read p50/p95/p99 separately and explain why each matters.
- Bottleneck triageYou correlate metrics across application, database, and infrastructure layers.
- Capacity instinctsYou can translate a soak test into a sizing or scaling recommendation.