servant-prometheus: Helpers for using prometheus with servant

[ bsd3, library, servant, system, web ] [ Propose Tags ]


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Versions [RSS] 1.0.0, 1.1.0, 1.2.0
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Dependencies base (>=4.10 && <4.18), clock (>=0.8.3 && <0.9), ghc-prim (>=0.8.0 && <0.10), hashable (>=1.4.2 && <1.5), http-types (>=0.12.3 && <0.13), prometheus-client (>=1.1.0 && <1.2), servant (>=0.14 && <0.20), text (>=1.2.5 && <2.1), wai (>=3.2.3 && <3.3) [details]
License BSD-3-Clause
Author Andrii Demydenko <>, Anchor Engineering <>, Servant Contributors
Maintainer Andrii Demydenko <>
Category Servant, Web, System
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Source repo head: git clone
Uploaded by worm2fed at 2023-10-02T13:20:53Z
Downloads 167 total (19 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
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Status Docs available [build log]
Last success reported on 2023-10-02 [all 1 reports]

Readme for servant-prometheus-1.1.0

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Servant Performance Counters

This package lets you track performance counters for each of your Servant endpoints using Prometheus.


Servant-Prometheus knows how to handle all official Servant combinators out of the box.

Instrumenting your API

To use Servant-Prometheus, you'll need to wrap your WAI application with the Servant-Prometheus middleware.

import Network.Wai.Handler.Warp
import Prometheus.Servant

main :: IO ()
main = do
  let api    = ...
      server = ...
      app = prometheusMiddleware defaultMetrics api server

  run 8080 app

Runtime overhead

Instrumenting your API introduces a non-zero runtime overhead, on the order of 200 - 600 ┬Ásec depending upon your machine. It's a good idea to run the benchmarks on your intended production platform to get an idea of how large the overhead will be. You'll need to have wrk installed to run the benchmarks.

In general, the runtime overhead should be effectively negligible if your handlers are issuing network requests, such as to databases. If you have handlers that are small, CPU-only, and requested frequently, you will see a performance hit from servant-prometheus.