k6의 사용자 지정 메트릭 및 추세

k6 ships with built-in metrics like http_req_duration, but advanced tests often need to measure domain-specific values: items in a cart, business transaction time, or a custom error rate. k6 lets you create custom metrics.

k6 offers four custom metric types from k6/metrics:

• Counter — cumulative sum.
• Gauge — last recorded value.
• Rate — percentage of non-zero/true values.
• Trend — statistics like min, max, avg, p95.

Import the constructors you need and create the metric objects in module scope so they are shared across iterations.

A Counter accumulates a value over the whole test. Here we count how many orders were created.

A Trend collects a series of numbers and reports statistics. It is ideal for timing custom logic.

A Rate tracks how often a condition is true. Add true or false and k6 reports the percentage of trues.

A Gauge keeps only the most recent value you add. Use it for things like the current queue length reported by an endpoint.

Just like built-in metrics, you can attach tags when adding a value. This lets you slice your custom metric by endpoint or feature.

Custom metrics integrate fully with thresholds. You can fail a run if your business metric crosses a limit.

At the end of a run, custom metrics appear in the end-of-test summary alongside built-in ones, showing the appropriate statistics for their type.

Picking the correct metric type matters: use a Trend for durations, a Rate for success ratios, a Counter for totals, and a Gauge for snapshot values. The wrong type gives misleading summaries.

You can now extend k6 with custom metrics.

• Counter sums, Gauge keeps the last value, Rate tracks ratios, Trend reports stats.
• Add tags and thresholds to custom metrics for targeted SLOs.
• They appear in the summary and any output backend.