Instrument client-go requests

This change adds 3 metrics tracking client-go requests to the Kubernetes
API:

* `prometheus_operator_kubernetes_client_http_requests_total`, counter
  with a `status_code` label.
* `prometheus_operator_kubernetes_client_http_request_duration_seconds`,
  summary with a `endpoint` label.
* `prometheus_operator_kubernetes_client_rate_limiter_duration_seconds`,
  summary with a `endpoint` label.

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

cmd/operator/main.go

@@ -32,6 +32,7 @@ import (
 	"github.com/prometheus-operator/prometheus-operator/pkg/admission"
 	alertmanagercontroller "github.com/prometheus-operator/prometheus-operator/pkg/alertmanager"
 	"github.com/prometheus-operator/prometheus-operator/pkg/api"
+	"github.com/prometheus-operator/prometheus-operator/pkg/k8sutil"
 	"github.com/prometheus-operator/prometheus-operator/pkg/operator"
 	prometheuscontroller "github.com/prometheus-operator/prometheus-operator/pkg/prometheus"
 	thanoscontroller "github.com/prometheus-operator/prometheus-operator/pkg/thanos"
@@ -248,6 +249,8 @@ func Main() int {
 	wg, ctx := errgroup.WithContext(ctx)
 	r := prometheus.NewRegistry()
 
+	k8sutil.MustRegisterClientGoMetrics(r)
+
 	po, err := prometheuscontroller.New(ctx, cfg, log.With(logger, "component", "prometheusoperator"), r)
 	if err != nil {
 		fmt.Fprint(os.Stderr, "instantiating prometheus controller failed: ", err)

pkg/k8sutil/metrics.go

@@ -0,0 +1,87 @@
+// Copyright 2020 The prometheus-operator Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package k8sutil
+
+import (
+	"net/url"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"k8s.io/client-go/tools/metrics"
+)
+
+type clientGoHTTPMetricAdapter struct {
+	count    *prometheus.CounterVec
+	duration *prometheus.SummaryVec
+}
+
+type clientGoRateLimiterMetricAdapter struct {
+	duration *prometheus.SummaryVec
+}
+
+// MustRegisterClientGoMetrics registers k8s.io/client-go metrics.
+// It panics if it encounters an error (e.g. metrics already registered).
+func MustRegisterClientGoMetrics(registerer prometheus.Registerer) {
+	httpMetrics := &clientGoHTTPMetricAdapter{
+		count: prometheus.NewCounterVec(
+			prometheus.CounterOpts{
+				Name: "prometheus_operator_kubernetes_client_http_requests_total",
+				Help: "Total number of Kubernetes's client requests by status code.",
+			},
+			[]string{"status_code"},
+		),
+		duration: prometheus.NewSummaryVec(
+			prometheus.SummaryOpts{
+				Name:       "prometheus_operator_kubernetes_client_http_request_duration_seconds",
+				Help:       "Summary of latencies for the Kubernetes client's requests by endpoint.",
+				Objectives: map[float64]float64{},
+			},
+			[]string{"endpoint"},
+		),
+	}
+
+	rateLimiterMetrics := &clientGoRateLimiterMetricAdapter{
+		duration: prometheus.NewSummaryVec(
+			prometheus.SummaryOpts{
+				Name:       "prometheus_operator_kubernetes_client_rate_limiter_duration_seconds",
+				Help:       "Summary of latencies for the Kuberntes client's rate limiter by endpoint.",
+				Objectives: map[float64]float64{},
+			},
+			[]string{"endpoint"},
+		),
+	}
+
+	metrics.Register(
+		metrics.RegisterOpts{
+			RequestLatency:     httpMetrics,
+			RequestResult:      httpMetrics,
+			RateLimiterLatency: rateLimiterMetrics,
+		},
+	)
+
+	registerer.MustRegister(httpMetrics.count, httpMetrics.duration, rateLimiterMetrics.duration)
+}
+
+func (a *clientGoHTTPMetricAdapter) Increment(code string, method string, host string) {
+	a.count.WithLabelValues(code).Inc()
+}
+
+func (a *clientGoHTTPMetricAdapter) Observe(verb string, u url.URL, latency time.Duration) {
+	a.duration.WithLabelValues(u.EscapedPath()).Observe(latency.Seconds())
+}
+
+func (a *clientGoRateLimiterMetricAdapter) Observe(verb string, u url.URL, latency time.Duration) {
+	a.duration.WithLabelValues(u.EscapedPath()).Observe(latency.Seconds())
+}