Part 3 of 4: Custom Metrics, Stress Testing, and Web Vitals — Going Beyond Basic Load Testing with k6
In part 2 I built a layered test suite against Google's Online Boutique on a homelab Kubernetes cluster. Smoke passed. The load test ran clean after fixing two bugs, a wrong assertion string on checkout and a missing await in the browser scenario. The load test summary showed p95 response times at 273ms, checkout success at 100%, and a CLS score of 0.117 nudging just over the 0.10 threshold.
That left three things unfinished. The stress test hadn't run. The CLS finding had no explanation. And the four custom metric types I'd defined in the scenarios deserved more than a passing mention.
This post runs the stress test, reads the results architecturally, explains what CLS 0.117 actually means and why HTTP testing would never have surfaced it, and walks through all four custom metric types with concrete examples of when each one is the right tool.
All the code is here: https://github.com/mwimpelberg28/k6-playground
