[FLORA-235] Re-enable prometheus metrics for http & process resources (…

…#802)

changelog.d/801

@@ -0,0 +1,2 @@
+synopsis: Re-enable prometheus metrics for http & process resources
+prs: #802

flora.cabal

@@ -27,13 +27,13 @@ flag prod
 
 common common-extensions
   default-extensions:
-    NoStarIsType
     DataKinds
     DeriveAnyClass
     DerivingStrategies
     DerivingVia
     DuplicateRecordFields
     LambdaCase
+    NoStarIsType
     OverloadedLabels
     OverloadedRecordDot
     OverloadedStrings
@@ -347,7 +347,7 @@ library flora-web
   build-depends:
     , aeson
     , async
-    , base                      ^>=4.18.2
+    , base                       ^>=4.18.2
     , base32
     , bytestring
     , Cabal-syntax
@@ -381,13 +381,16 @@ library flora-web
     , mtl
     , network-uri
     , odd-jobs
-    , one-time-password         ==3.0.0.0
+    , one-time-password          ==3.0.0.0
     , openapi3
     , optics-core
     , pg-entity
     , pg-transact-effectful
     , postgresql-simple
     , pretty
+    , prometheus-client
+    , prometheus-metrics-ghc
+    , prometheus-proc
     , PyF
     , raven-haskell
     , resource-pool
@@ -411,6 +414,7 @@ library flora-web
     , wai-app-static
     , wai-log
     , wai-middleware-heartbeat
+    , wai-middleware-prometheus
     , warp
     , xml-conduit
     , xml-conduit-writer

src/web/FloraWeb/Server.hs

@@ -33,10 +33,14 @@ import Network.Wai.Handler.Warp
   )
 import Network.Wai.Log qualified as WaiLog
 import Network.Wai.Middleware.Heartbeat (heartbeatMiddleware)
+import Network.Wai.Middleware.Prometheus qualified as P
 import OddJobs.Endpoints qualified as OddJobs
 import OddJobs.Job (startJobRunner)
 import OddJobs.Types qualified as OddJobs
 import Optics.Core
+import Prometheus qualified as P
+import Prometheus.Metric.GHC qualified as P
+import Prometheus.Metric.Proc qualified as P
 import Sel
 import Servant
   ( Application
@@ -106,6 +110,10 @@ runFlora =
             let baseURL = "http://localhost:" <> display env.httpPort
             liftIO $ blueMessage $ "🌺 Starting Flora server on " <> baseURL
             liftIO $ when (isJust env.mltp.sentryDSN) (blueMessage "📋 Connecting to Sentry endpoint")
+            liftIO $ when env.mltp.prometheusEnabled $ do
+              blueMessage $ "🔥 Exposing Prometheus metrics at " <> baseURL <> "/metrics"
+              void $ P.register P.ghcMetrics
+              void $ P.register P.procMetrics
             liftIO $ when env.mltp.zipkinEnabled (blueMessage "🖊️ Connecting to Zipkin endpoint")
             liftIO $ when (env.environment == Development) (blueMessage "🔁 Live reloading enabled")
             let withLogger = Logging.makeLogger env.mltp.logger
@@ -169,7 +177,9 @@ runServer appLogger floraEnv = do
     $ heartbeatMiddleware
       . loggingMiddleware
       . const
-    $ server
+    $ P.prometheus
+      P.def
+      server
 
 mkServer
   :: Logger