Prometheus remote write
Caution: This is an experimental module.
While we intend to keep experimental modules as stable as possible, we may need to introduce breaking changes. This could happen at future k6 releases until the module becomes fully stable and graduates as a k6 core module. For more information, refer to the extension graduation process.
Experimental modules maintain a high level of stability and follow regular maintenance and security measures. Feel free to open an issue if you have any feedback or suggestions.
For instance, when using the
experimental-prometheus-rw output, k6 can send test-result metrics to the remote-write endpoint and store them in Prometheus.
The output, during the
k6 run execution, gets all the generated time-series data points for the k6 metrics.
It then generates the equivalent Prometheus time series and sends them to the Prometheus remote write endpoint.
All k6 metric types are converted into an equivalent Prometheus metric type. 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
- 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.
|Trend||Counter and Gauges (default) or Native Histogram|
Trend metric conversions
This output provides two distinct mechanisms to send k6 Trend metrics to Prometheus:
Both options provide efficient storage of test results while providing high-precision queries.
Note that k6 aggregates trend metric data before sending it to Prometheus in both options. The reasons for aggregating data are:
- Prometheus stores data in a millisecond precision (
ms), but k6 metrics collect data points with higher accuracy, nanosecond (
- A load test could generate vast amounts of data points. High-precision raw data could quickly become expensive and complex to scale and is unnecessary when analyzing performance trends.
1. Counter and gauges
By default, Prometheus supports Counter and Gauge Metric types. Therefore, this option is the default of this output and converts all the k6
Trend metrics to Counter and Gauges Prometheus metrics.
You can configure how to convert all the k6 trend metrics with the
K6_PROMETHEUS_RW_TREND_STATS option that accepts a comma-separated list of stats functions:
p(x). The default is
Given the list of stats functions, k6 converts all trend metrics to the respective math functions as Prometheus metrics.
K6_PROMETHEUS_RW_TREND_STATS=p(90),p(95),max transforms each trend metric into three Prometheus metrics as follows:
This option provides a configurable solution to represent
Trend metrics in Prometheus but has the following drawbacks:
- Convert a k6
Trendmetric to several Prometheus metrics.
- It is impossible to aggregate some gauge values (especially percentiles).
- It uses a memory-expensive k6 data structure.
2. Prometheus native histogram
To address the limitations of the previous option, you can convert k6 trend metrics to high-fidelity histograms enabling Prometheus native histograms.
With this option, each k6 trend metric maps to its corresponding Prometheus histogram metric:
k6_*. You can then query them using Prometheus histogram functions, such as histogram_quantile().
🌟 To learn the benefits and outcomes of using Histograms, watch High-resolution Histograms in Prometheus.
⚠️ Note that Native Histogram is an experimental feature released in Prometheus v2.40.0, and other remote write implementations might not support it yet. In the future, when Prometheus makes this feature stable, k6 will consider using it as the default conversion method for Trend metrics.
Send test metrics to a remote write endpoint
To send k6 metrics to a remote write endpoint without native histograms:
Set up a running remote write endpoint and ensure k6 can reach it.
Run your k6 script with the
--outflag and the URL of the RW endpoint as follows:
K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \ k6 run -o experimental-prometheus-rw script.js
HTTP Basic Authenticationbash
K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \ K6_PROMETHEUS_RW_USERNAME=USERNAME \ K6_PROMETHEUS_RW_PASSWORD=PASSWORD \ k6 run -o experimental-prometheus-rw script.js
- Optionally, pass the
K6_PROMETHEUS_RW_TREND_STATSto gain the ability to query additional stats for trend metrics. The default is
K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \ K6_PROMETHEUS_RW_TREND_STATS=p(95),p(99),min,max \ k6 run -o experimental-prometheus-rw script.js
To send k6 metrics to a remote write endpoint with native histograms:
Enable the feature flag –enable-feature=native-histograms in Prometheus 2.40.0 or higher. Set up a running remote write endpoint and ensure k6 can reach it.
Run your k6 script with the
--outflag, enabling the
K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAMoption, and the URL of the RW endpoint as follows:
K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \ K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true \ k6 run -o experimental-prometheus-rw script.js
HTTP Basic Authenticationbash
K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \ K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true \ K6_PROMETHEUS_RW_USERNAME=USERNAME \ K6_PROMETHEUS_RW_PASSWORD=PASSWORD \ k6 run -o experimental-prometheus-rw script.js
When running the previous
k6 run commands, k6 starts sending time-series metrics to Prometheus.
All the time series have a
In the Prometheus Web UI, they appear like this:
k6 has special options for remote write output.
|URL of the Prometheus remote write implementation’s endpoint. Default is |
|Additional header to include in the HTTP requests. It can be set using the described format, for example |
|A comma-separated list of key-values||Additional headers to include in the HTTP requests. |
|Interval between the metrics’ aggregation and upload to the endpoint. Default is |
|If true, maps all the defined trend metrics as Native Histograms. Default is |
|list of ||If Native Histogram is not enabled, then it defines the stats functions to map for all of the defined trend metrics. It’s a comma-separated list of stats functions to include (e.g. |
|If true, the HTTP client skips TLS verification on the endpoint. Default is |
|If true, the output at the end of the test marks all the seen time series as stale. Default is |
|Username for the HTTP Basic authentication at the Prometheus remote write endpoint.|
|Password for the HTTP Basic authentication at the Prometheus remote write endpoint.|
|A path to the PEM (Privacy-Enhanced Mail) formatted client certificate.|
|A path to the PEM formatted client private key.|
|Sets the Authorization Bearer Token Header.|
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
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.
Time series visualization
To visualize time series with Grafana, you can use the Explore UI or import any of the existing pre-built dashboards:
- k6 Prometheus dashboard by Grafana k6
- k6 Prometheus (Native Histograms) dashboard by Grafana k6
- Other public dashboards available from the community
If you are a Grafana Cloud user, please refer to the Grafana Cloud Prometheus docs.
For a local environment, the
xk6-output-prometheus-remote repository includes a docker-compose setup that provisions the
k6 Prometheus and
k6 Prometheus (Native Histograms) dashboards:
Docker compose example
Clone the repository to get started and follow these steps for using the docker-compose.yml file that starts Prometheus and Grafana:
Start the docker compose environment.shell
docker compose up -d prometheus grafanashell
# Output Creating xk6-output-prometheus-remote_grafana_1 ... done Creating xk6-output-prometheus-remote_prometheus_1 ... done
Prometheus is started with Native Histogram enabled. You can use the same Prometheus instance to receive k6 trend metrics as native histograms or multiple metric stats.
Run the k6 test with one of the options detailed on Send test metrics to a remote write endpoint.
K6_PROMETHEUS_RW_TREND_STATS=p(95),p(99),min,max \ k6 run -o experimental-prometheus-rw script.js
K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true \ k6 run -o experimental-prometheus-rw script.js
Optionally, you can set the
testidtag as a wide test tag to segment metrics into discrete test runs and filter specific test results on the pre-built Grafana dashboards or in PromQL queries.
testidcan be any unique string that let you clearly identify the test run.
K6_PROMETHEUS_RW_TREND_STATS=p(95),p(99),min,max \ k6 run -o experimental-prometheus-rw --tag testid=<SET-HERE-A-UNIQUE-ID> script.js
K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true \ k6 run -o experimental-prometheus-rw --tag testid=<SET-HERE-A-UNIQUE-ID> script.js
After running the test, visit http://localhost:3000. If you enabled native histograms, select the k6 Prometheus (Native Histograms) dashboard; otherwise, select the k6 Prometheus Dashboard.