6 Lessons Learned from Optimizing the Performance of a Node.js Service
Article Summary
Klarna's A/B testing platform needed single-digit millisecond latency at 99.9%. Their Node.js service was spiking to seconds under load.
The team built a performance testing pipeline to catch issues before production. What they discovered through load testing revealed hidden bottlenecks that standard monitoring completely missed.
Key Takeaways
- DNS resolution created tens of thousands of queued requests from StatsD client
- Batching Kafka messages every second eliminated multi-second response time spikes
- Event loop metrics (Active Requests/Handles) exposed problems CPU/memory didn't show
- Extended 10-minute tests revealed issues that 2-minute tests completely missed
Critical Insight
Six optimization lessons transformed a Node.js service from unpredictable multi-second spikes to consistent sub-millisecond performance under sustained load.
