feat: expose HTTP requests metrics

Signed-off-by: Vivek Singh <[email protected]>

.golangci.yml

@@ -32,6 +32,5 @@ linters:
     - goerr113
     - exhaustivestruct
     - lll
-
 service:
   golangci-lint-version: 1.45.x

internal/webserver/middleware/metrics.go

@@ -0,0 +1,66 @@
+// Copyright 2022 Clastix Labs
+// SPDX-License-Identifier: Apache-2.0
+
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+func init() {
+	_ = prometheus.Register(totalRequests)
+	_ = prometheus.Register(httpDuration)
+}
+
+type httpResponseWriter struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func newHTTPResponseWriter(w http.ResponseWriter) *httpResponseWriter {
+	return &httpResponseWriter{
+		w,
+		http.StatusOK,
+	}
+}
+
+func (h *httpResponseWriter) WriteHeader(statusCode int) {
+	h.statusCode = statusCode
+	h.ResponseWriter.WriteHeader(statusCode)
+}
+
+var totalRequests = prometheus.NewCounterVec(
+	prometheus.CounterOpts{
+		Name: "capsule_proxy_requests_total",
+		Help: "Number of requests",
+	},
+	[]string{"path", "status"},
+)
+
+var httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	Name: "capsule_proxy_response_time_seconds",
+	Help: "Duration of capsule proxy requests.",
+}, []string{"path"})
+
+func MetricsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		route := mux.CurrentRoute(r)
+		path, _ := route.GetPathTemplate()
+
+		timer := prometheus.NewTimer(httpDuration.WithLabelValues(path))
+
+		rw := newHTTPResponseWriter(w)
+		next.ServeHTTP(rw, r)
+
+		statusCode := rw.statusCode
+
+		totalRequests.WithLabelValues(path, strconv.Itoa(statusCode)).Inc()
+
+		timer.ObserveDuration()
+	})
+}

internal/webserver/middleware/metrics_test.go

@@ -0,0 +1,90 @@
+// Copyright 2022 Clastix Labs
+// SPDX-License-Identifier: Apache-2.0
+
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
+	model "github.com/prometheus/client_model/go"
+)
+
+func dummyHandler(w http.ResponseWriter, r *http.Request) {
+	_, _ = w.Write([]byte("hello"))
+	w.WriteHeader(http.StatusOK)
+}
+
+func newRequest(method, url string) (*http.Request, error) {
+	req, err := http.NewRequest(method, url, nil)
+	return req, err
+}
+
+func Test_MetricsMiddleware_RequestCount(t *testing.T) {
+	testCases := []struct {
+		name         string
+		requestCount int
+		path         string
+		output       float64
+	}{
+		{
+
+			name:         "single request count",
+			requestCount: 1,
+			path:         "/test",
+			output:       1,
+		},
+	}
+
+	for _, test := range testCases {
+		router := mux.NewRouter()
+		router.HandleFunc(test.path, dummyHandler).Methods("GET")
+		router.Use(MetricsMiddleware)
+
+		rw := httptest.NewRecorder()
+
+		for i := 0; i < test.requestCount; i++ {
+			req, err := newRequest("GET", test.path)
+			if err != nil {
+				t.Errorf("failed to create HTTP request object")
+			}
+			router.ServeHTTP(rw, req)
+		}
+
+		t.Run("regular middleware call", func(t *testing.T) {
+			ch := make(chan prometheus.Metric)
+			go totalRequests.Collect(ch)
+			g := (<-ch).(prometheus.Counter)
+			result := readVector(g)
+			if test.output != result.value {
+				t.Errorf("testcase %s failed. expected: %f, got: %f", test.name, test.output, result.value)
+			}
+		})
+	}
+}
+
+type metricResult struct {
+	value  float64
+	labels map[string]string
+}
+
+func labels2Map(labels []*model.LabelPair) map[string]string {
+	res := map[string]string{}
+	for _, l := range labels {
+		res[l.GetName()] = l.GetValue()
+	}
+	return res
+}
+
+func readVector(g prometheus.Metric) metricResult {
+	m := &model.Metric{}
+	_ = g.Write(m)
+
+	return metricResult{
+		value:  m.GetCounter().GetValue(),
+		labels: labels2Map(m.GetLabel()),
+	}
+}

internal/webserver/webserver.go

@@ -19,6 +19,7 @@ import (
 	"github.com/gorilla/handlers"
 	"github.com/gorilla/mux"
 	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"golang.org/x/net/http/httpguts"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/util/sets"
@@ -259,14 +260,17 @@ func (n kubeFilter) registerModules(ctx context.Context, root *mux.Router) {
 func (n kubeFilter) Start(ctx context.Context) error {
 	r := mux.NewRouter().StrictSlash(true)
 	r.Use(handlers.RecoveryHandler())
+
 	r.Path("/_healthz").Subrouter().HandleFunc("", func(writer http.ResponseWriter, request *http.Request) {
 		writer.WriteHeader(200)
 		_, _ = writer.Write([]byte("ok"))
 	})
+	r.Path("/_metrics").Subrouter().Handle("", promhttp.Handler())
 
 	root := r.PathPrefix("").Subrouter()
 	n.registerModules(ctx, root)
 	root.Use(
+		middleware.MetricsMiddleware,
 		n.reverseProxyMiddleware,
 		middleware.CheckPaths(n.client, n.log, n.allowedPaths, n.impersonateHandler),
 		middleware.CheckAuthorization(n.client, n.log, n.serverOptions.IsListeningTLS()),