healthz is a middleware

src/Application.hs

@@ -29,7 +29,7 @@ import Data.WebsiteContent
 import Database.Persist.Postgresql (PostgresConf(..))
 import Import hiding (catch)
 import Language.Haskell.TH.Syntax (qLocation)
-import Network.Wai (Middleware, rawPathInfo)
+import Network.Wai (Middleware, rawPathInfo, pathInfo, responseBuilder)
 import Network.Wai.Handler.Warp (Settings, defaultSettings,
                                  defaultShouldDisplayException, getPort,
                                  runSettings, setHost, setOnException, setPort)
@@ -91,6 +91,7 @@ makeApplication foundation = do
     appPlain <- toWaiAppPlain foundation
 
     let middleware = id -- prometheus def
+                   . healthz
 #if !DEVELOPMENT
                    . forceSSL' (appSettings foundation)
 #endif
@@ -101,6 +102,13 @@ makeApplication foundation = do
 
     return (middleware appPlain)
 
+-- | Bypass any overhead from Yesod
+healthz :: Middleware
+healthz app req send =
+  case pathInfo req of
+    ["healthz"] -> send $ responseBuilder status200 [("content-type", "text/plain; charset=utf-8")] "OK"
+    _ -> app req send
+
 forceSSL' :: AppSettings -> Middleware
 forceSSL' settings app
     | appForceSsl settings = \req send ->

src/Handler/Home.hs

@@ -17,7 +17,7 @@ import Stackage.Database
 import Yesod.GitRepo (grContent)
 
 getHealthzR :: Handler String
-getHealthzR = return "OK"
+getHealthzR = return "This should never be used, we should use the middleware instead"
 
 -- This is a handler function for the G request method on the HomeR
 -- resource pattern. All of your resource patterns are defined in