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Prometheus remote write

Experimental module, use at your own risk

While we intend to keep this module as simple and stable as possible, we may need to add features or introduce breaking changes. This could happen at any time until we release this module as stable.

Feel free to provide user feedback, and open an issue or pull request if you have any suggestions.

Prometheus remote write is a protocol that makes it possible to reliably propagate data in real-time from a sender to a receiver. It has a defined specification and multiple implementations. For example, you can store the metrics in Prometheus. For other implementations, check the Prometheus Integrations guide.

With the Prometheus remote write output, k6 can send test-result metrics to a Prometheus remote write endpoint. The output during the k6 run execution gets all the generated data points for the built-in k6 metrics. It then generates the equivalent Prometheus remote write time series.

note

If you want to export cloud results to remote write, refer to Cloud to Prometheus RW.

About metrics mapping

All k6 metric types are converted into an equivalent Prometheus remote write type:

k6PrometheusName label
CounterCounterk6_*_total
GaugeGaugek6_*_<unit-suffix>
RateGaugek6_*_rate
TrendGauges / Native Histogramk6_*_<unit-suffix>

Trend metric conversion

By default, k6 trend metrics convert to primitive counters and gauges. To convert trend metrics to high-fidelity histograms, you can use Prometheus Native histogram instead.

Because k6 can't easily determine fixed buckets in advance, k6 metrics can't export to the original Prometheus histograms. So, the output maps a trend metric into primitive counter and gauges. Each value represents a math function (count, sum, min, max, avg, med, p(x)). This mapping has following drawbacks:

  • It is impossible to aggregate some gauge values (especially percentiles).
  • It uses a memory-expensive k6 data structure.

To resolve these limitations, you can map a trend as a Prometheus Native Histogram. To do this, you can use the K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true environment variable (or one of the other ways). The output then converts all the trend types into a dedicated Native Histogram.

Mapping trends as native histograms gives you more efficient storage and more precise queries. The drawback is that the feature is experimental, released in Prometheus v2.40.0.

note

Native Histogram is an experimental feature, so it has to be enabled (--enable-feature=native-histograms). Other remote write implementations might not support it yet.

Naming conventions

The output maps the metrics into time series with Name labels. As much as possible, k6 respects the naming best practices that the Prometheus project defines:

  • All time series are prefixed with the k6_ namespace.
  • All time series are suffixed with the base unit of the sample value (if k6 knows what the base unit is).
  • Trends and rates have the relative suffixes, to make them more discoverable.

Stale trend metrics

This k6 output can mark the time series at the end of the test as stale. To enable the stale marker option, set the K6_PROMETHEUS_RW_STALE_MARKERS environment variable to true.

By default, the metrics are active for 5 minutes after the last flushed sample. They are automatically marked as stale after. For details about staleness, refer to the Prometheus docs.

Send test metrics to a remote write endpoint

Prometheus as remote write agent

To use remote write in Prometheus 2.x, use the --web.enable-remote-write-receiver flag. The xk6 extension repository has some docker compose examples in the example directory. For remote write storage options, refer to the Prometheus docs.

To send k6 metrics to a remote write endpoint, follow these steps:

  1. Set up a running remote write endpoint with an endpoint that k6 can reach.

  2. Run your k6 script, using the --out flag with experimental-prometheus-rw as the argument:

    k6 run -o experimental-prometheus-rw script.js

All the time series have a k6_ prefix. In the Metric Explorer UI in Grafana, it looks something like this:

k6 metrics as seen in the Prometheus UI

Authenticate

If the remote write endpoint requires authentication, the output supports the HTTP Basic authentication and it can be used with the following command:

K6_PROMETHEUS_RW_USERNAME=foo \
K6_PROMETHEUS_RW_PASSWORD=bar \
./k6 run script.js -o experimental-prometheus-rw

Feel free to request more authentication methods or provide your experience in the issue tracker.

Options

k6 has special options for remote write output.

NameTypeDefaultDescription
K6_PROMETHEUS_RW_SERVER_URLstringhttp://localhost:9090/api/v1/writeURL of the Prometheus remote write implementation's endpoint.
K6_PROMETHEUS_RW_HEADERS_<here-the-header-key>list of stringAdditional headers to include in the HTTP requests. K6_PROMETHEUS_RW_HEADERS_X-MY-HEADER=foo
K6_PROMETHEUS_RW_USERNAMEstringUser for the HTTP Basic authentication at the Prometheus remote write endpoint.
K6_PROMETHEUS_RW_PASSWORDstringPassword for the HTTP Basic authentication at the Prometheus remote write endpoint.
K6_PROMETHEUS_RW_PUSH_INTERVALstring5sInterval of the metrics' aggregation and upload to the endpoint.
K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAMbooleanfalseIf true, it maps the all defined trend metrics as Native Histograms.
K6_PROMETHEUS_RW_TREND_STATSlist of stringp(99)If Native Histogram is not enabled then it defines the stats functions to map for the all defined trend metrics. It's a comma-separated list of stats functions to include (e.g. p(90),avg,sum). Check the trend section to know the entire set of the supported stats.
K6_PROMETHEUS_RW_INSECURE_SKIP_TLS_VERIFYbooleanfalseIf true, the HTTP client skips TLS verification on the endpoint.
K6_PROMETHEUS_RW_STALE_MARKERSbooleanfalseIf true, the output at the end of the test marks all the seen time series as stale.

Time series visualization

To visualize time series, you can use the Grafana Cloud integration.

If you want a local option instead, the xk6 extension repository includes a docker-compose setup with two pre-built Grafana dashboards. You can use these dashboards to visualize the generated time series with Prometheus configured as a data source:

  • visualize the results of a test run
  • list test runs

Prometheus k6 results