k6

What it does

k6 is an open-source load and performance testing tool that executes test scenarios written in JavaScript. It simulates thousands of virtual users (VUs) to test the resilience, throughput, and latency of APIs and microservices with native CI/CD integration.

Why it’s interesting

Legacy tools like JMeter are heavyweight and use XML configs that don't version well. k6 lets developers write tests in modern JavaScript with modular imports, runs thousands of VUs from a laptop, and enforces Service Level Objectives (SLOs) as code directly in pull requests.

Real-world use case

Add a load test script to your FastAPI repository and run it in GitHub Actions before each release. Ramp up 200 concurrent users over 3 minutes, automatically fail the build if p95 response time exceeds 250ms or error rates exceed 1%.

What I can learn

• 01

  High-Concurrency Virtual User Scheduling

  Learn how k6 uses goroutines and non-blocking I/O to simulate thousands of simultaneous connections on a single machine with minimal memory overhead.

• 02

  Embedding JavaScript Engines in Systems Code

  Study how k6 embeds the ECMAScript engine (goja) to execute user scripts without requiring an external Node.js runtime.

• 03

  Declarative SLO Thresholds and Metrics

  Understand how real-time counters, gauges, and histograms are collected and dynamically evaluated to determine test success or failure.

One thing to explore

JavaScript Module Bridge and Virtual User Orchestration

Inspect pkg/lib/ and js/ directories to see how ES6 modules are bridged to Go network clients and how VU iterations are scheduled.