track response time for http endpoints (#1412)

* track response time for http endpoints

cmd/jimmsrv/service/service.go

@@ -273,6 +273,8 @@ func NewService(ctx context.Context, p Params) (*Service, error) {
 	s := new(Service)
 	s.mux = chi.NewRouter()
 
+	s.mux.Use(middleware.MeasureHTTPResponseTime)
+
 	// Setup all dependency services
 
 	if p.ControllerUUID == "" {

internal/middleware/responsetime.go

@@ -0,0 +1,44 @@
+// Copyright 2024 Canonical.
+
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+
+	"github.com/canonical/jimm/v3/internal/servermon"
+)
+
+// statusRecorder to record the status code from the ResponseWriter
+type statusRecorder struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (rec *statusRecorder) WriteHeader(statusCode int) {
+	rec.statusCode = statusCode
+	rec.ResponseWriter.WriteHeader(statusCode)
+}
+
+// MeasureHTTPResponseTime tracks response time of HTTP requests.
+// We don't track websocket requests.
+func MeasureHTTPResponseTime(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Check the upgrade header because we only track http endpoints
+		if r.Header.Get("Upgrade") == "websocket" {
+			next.ServeHTTP(w, r)
+			return
+		}
+		rec := statusRecorder{w, 200}
+		start := time.Now()
+		defer func() {
+			route := chi.RouteContext(r.Context()).RoutePattern()
+			statusCode := strconv.Itoa(rec.statusCode)
+			servermon.ResponseTimeHistogram.WithLabelValues(route, r.Method, statusCode).Observe(time.Since(start).Seconds())
+		}()
+		next.ServeHTTP(&rec, r)
+	})
+}

internal/servermon/monitoring.go

@@ -131,6 +131,13 @@ var (
 		Name:      "controller",
 		Help:      "The number of controllers managed by JIMM.",
 	})
+	ResponseTimeHistogram = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: "jimm",
+		Subsystem: "http",
+		Name:      "request_duration_seconds",
+		Help:      "The duration of handling an HTTP request in seconds.",
+		Buckets:   []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10},
+	}, []string{"route", "method", "status_code"})
 )
 
 // DurationObserver returns a function that, when run with `defer` will