Network.Wai.Metrics

A WAI middleware to collect the following EKG metrics from compatible web servers:

• number of requests (counter wai.request_count)
• number of server errors (counter wai.server_error_count)
• latency distribution (distribution wai.latency_distribution)

Here's an example of reading these metrics from a Scotty server, and displaying them with EKG.

-- Compile with GHC option `-with-rtsopts=-T` for GC metrics
import Web.Scotty
import Control.Applicative
import System.Remote.Monitoring (serverMetricStore, forkServer)
import Network.Wai.Metrics

main :: IO()
main = do
  store <- serverMetricStore <$> forkServer "localhost" 8000
  waiMetrics <- registerWaiMetrics store
  scotty 3000 $ do
    middleware (metrics waiMetrics)
    get "/" $ html "Ping"

Now have a look at your local EKG instance and display the request count by clicking on 'wai.request_count'.

WAI metrics can also be stored in a bare EKG store, with no UI and no GC metrics. Use ekg-core's newStore function.

Compatible web servers include the following:

• Yesod
• Scotty
• Spock
• Servant
• Warp

Documentation

registerWaiMetrics :: Store -> IO WaiMetrics

Register in EKG a number of metrics related to web server activity.

• wai.request_count

• wai.server_error_count

• wai.latency_distribution

data WaiMetrics

The metrics to feed in WAI and register in EKG.

Constructors

WaiMetrics

Fields

requestCounter :: Counter

serverErrorCounter :: Counter

latencyDistribution :: Distribution

metrics :: WaiMetrics -> Middleware

Create a middleware to be added to a WAI-based webserver.