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CHANGELOG.md

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0.2.0.0

  • Minor changes in the interface of the library.
  • Significant changes in names of the exposed metrics.
  • Latency summaries (quantiles computed on the client side) are temporary not available. Histograms (quntiles computer on the server side) are not affected.
  • New module: Servant.Prometheus.Export.

Interface

  • makeMeters is not simply meters. It does not register anything but returns a Prometheus metric that you’ll need to register and then pass the result to monitorServant.
  • monitorServant no longer takes a proxy that specifies the server API as the API can be extracted from the type of the value that meters returns.

This brings the interface more in line with what prometheus-client provides for its own metric types.

In short, change:

meters <- SP.makeMeters appApi NoQuantiles
run {- ... -} $ SP.monitorServant appApi meters app

to

meters <- P.register $ SP.meters appApi
run {- ... -} $ SP.monitorServant meters app

Metric names

  • servant_path_<path>_<method>_http_status{status_code=<status>} → http_responses_total{path=<path>, method=<method>, status=<status>}
  • servant_path_<path>_<method>_in_flight → http_requests_in_flight{path=<path>, method=<method>}
  • servant_path_<path>_<method>_time_ms → http_request_duration_seconds{path=<path>, method=<method>} (the value is now in seconds rather than ms)

These names are more in line with the examples given in the Prometheus documentation. The path and method components have been moved from the metric name to labels to allow for aggregation over endpoints.

Example of a new metric:

http_responses_total{path="profile/:username",method="GET",status="2XX"} 5.0

Also now all metrics with all possible (according to the API definition) labels are initialised on start of the application in line with the recommendations from the Prometheus documentation.

Qunatiles

  • Histograms (buckets) are now computed unconditionally as their are cheap.
  • Default histogram buckets are slightly more fine-grained. They will become configurable in a future version.
  • Summaries are temporary unavilable. They will be brought in a future version and will be configurable per-endpoint as before.

Servant.Prometheus.Export

This new module containts utilities that allow you to easily export your app’s metrics through Servant.

If you use prometheus-client to keep track of your metrics, your servant app has some API (let’s call it yourApi), and you have implemented a server for it, that is, you have yourServer :: ServerT m yourApi, you can just wrap WithMetrics around yourApi and withMetrics yourApiProxy around yourServer and get the /metrics endpoint handled for you.

Internal changes

  • Bump LTS to 14.
  • Support servant 0.15 and 0.16.
  • Use getSystemTime instead of getCurrentTime.
  • Test are temporarily broken (please, help fix them!).