From 10717be2cc6d5295f2695eed953dacaf5fa4af74 Mon Sep 17 00:00:00 2001
From: Tom Wilkie <tom.wilkie@gmail.com>
Date: Wed, 6 Apr 2016 14:46:35 +0100
Subject: [PATCH] Insturment the app with prometheus.

---
 common/middleware/instrument.go | 46 +++++++++++++++++++++++++++++++++
 prog/app.go                     | 20 +++++++++++++-
 2 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100644 common/middleware/instrument.go

diff --git a/common/middleware/instrument.go b/common/middleware/instrument.go
new file mode 100644
index 0000000000..83fe533a3d
--- /dev/null
+++ b/common/middleware/instrument.go
@@ -0,0 +1,46 @@
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type Instrument struct {
+	RouteMatcher RouteMatcher
+	Duration     *prometheus.SummaryVec
+}
+
+// RouteMatcher is implemented by mux.Router.
+type RouteMatcher interface {
+	Match(*http.Request, *mux.RouteMatch) bool
+}
+
+func (i Instrument) Wrap(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		begin := time.Now()
+		interceptor := &interceptor{ResponseWriter: w, statusCode: http.StatusOK}
+		next.ServeHTTP(interceptor, r)
+		var (
+			route  = i.getRouteName(r)
+			status = strconv.Itoa(interceptor.statusCode)
+			took   = time.Since(begin)
+		)
+		i.Duration.WithLabelValues(r.Method, route, status).Observe(float64(took.Nanoseconds()))
+	})
+}
+
+func (i Instrument) getRouteName(r *http.Request) string {
+	var routeMatch mux.RouteMatch
+	if !i.RouteMatcher.Match(r, &routeMatch) {
+		return "unmatched_path"
+	}
+	name := routeMatch.Route.GetName()
+	if name == "" {
+		return "unnamed_path"
+	}
+	return name
+}
diff --git a/prog/app.go b/prog/app.go
index 0f24112a4d..f5bd8264e3 100644
--- a/prog/app.go
+++ b/prog/app.go
@@ -16,6 +16,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/weaveworks/go-checkpoint"
 	"github.com/weaveworks/weave/common"
 
@@ -26,12 +27,25 @@ import (
 	"github.com/weaveworks/scope/probe/docker"
 )
 
+var (
+	requestDuration = prometheus.NewSummaryVec(prometheus.SummaryOpts{
+		Namespace: "scope",
+		Name:      "request_duration_nanoseconds",
+		Help:      "Time spent serving HTTP requests.",
+	}, []string{"method", "route", "status_code"})
+)
+
+func init() {
+	prometheus.MustRegister(requestDuration)
+}
+
 // Router creates the mux for all the various app components.
 func router(collector app.Collector, controlRouter app.ControlRouter, pipeRouter app.PipeRouter) http.Handler {
 	router := mux.NewRouter().SkipClean(true)
 
 	// We pull in the http.DefaultServeMux to get the pprof routes
 	router.PathPrefix("/debug/pprof").Handler(http.DefaultServeMux)
+	router.Path("/metrics").Handler(prometheus.Handler())
 
 	app.RegisterReportPostHandler(collector, router)
 	app.RegisterControlRoutes(router, controlRouter)
@@ -40,7 +54,11 @@ func router(collector app.Collector, controlRouter app.ControlRouter, pipeRouter
 
 	router.PathPrefix("/").Handler(http.FileServer(FS(false)))
 
-	return router
+	instrument := middleware.Instrument{
+		RouteMatcher: router,
+		Duration:     requestDuration,
+	}
+	return instrument.Wrap(router)
 }
 
 func awsConfigFromURL(url *url.URL) *aws.Config {