🌱metrics: Expose client-go metrics in metrics server

Problem: Currently the only client-side metric enabled in the controller
processes is `rest_client_requests_total`, which is pretty limited.

This patch starts exporting more client-side metrics offered by client-go in
the controller process by default by copying what `component-base` does for
core Kubernetes components.

Author: ahmetb

pkg/metrics/client_go_adapter.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2018 The Kubernetes Authors.
+Copyright 2025 The Kubernetes Authors.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -18,6 +18,8 @@ package metrics
 
 import (
 	"context"
+	"net/url"
+	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	clientmetrics "k8s.io/client-go/tools/metrics"
@@ -28,7 +30,59 @@ import (
 // from Kubernetes so that we match the core controllers.
 
 var (
-	// client metrics.
+	// client metrics from https://github.com/kubernetes/kubernetes/blob/v1.33.0/staging/src/k8s.io/component-base/metrics/prometheus/restclient/metrics.go
+	// except for rest_client_exec_plugin_* metrics which controllers wouldn't use
+
+	// requestLatency is a Prometheus Histogram metric type partitioned by
+	// "verb", and "host" labels. It is used for the rest client latency metrics.
+	requestLatency = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "rest_client_request_duration_seconds",
+			Help:    "Request latency in seconds. Broken down by verb, and host.",
+			Buckets: []float64{0.005, 0.025, 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 15.0, 30.0, 60.0},
+		},
+		[]string{"verb", "host"},
+	)
+
+	// resolverLatency is a Prometheus Histogram metric type partitioned by
+	// "host" labels. It is used for the rest client DNS resolver latency metrics.
+	resolverLatency = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "rest_client_dns_resolution_duration_seconds",
+			Help:    "DNS resolver latency in seconds. Broken down by host.",
+			Buckets: []float64{0.005, 0.025, 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 15.0, 30.0},
+		},
+		[]string{"host"},
+	)
+
+	requestSize = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name: "rest_client_request_size_bytes",
+			Help: "Request size in bytes. Broken down by verb and host.",
+			// 64 bytes to 16MB
+			Buckets: []float64{64, 256, 512, 1024, 4096, 16384, 65536, 262144, 1048576, 4194304, 16777216},
+		},
+		[]string{"verb", "host"},
+	)
+
+	responseSize = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name: "rest_client_response_size_bytes",
+			Help: "Response size in bytes. Broken down by verb and host.",
+			// 64 bytes to 16MB
+			Buckets: []float64{64, 256, 512, 1024, 4096, 16384, 65536, 262144, 1048576, 4194304, 16777216},
+		},
+		[]string{"verb", "host"},
+	)
+
+	rateLimiterLatency = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "rest_client_rate_limiter_duration_seconds",
+			Help:    "Client side rate limiter latency in seconds. Broken down by verb, and host.",
+			Buckets: []float64{0.005, 0.025, 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 15.0, 30.0, 60.0},
+		},
+		[]string{"verb", "host"},
+	)
 
 	requestResult = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
@@ -37,6 +91,30 @@ var (
 		},
 		[]string{"code", "method", "host"},
 	)
+
+	requestRetry = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "rest_client_request_retries_total",
+			Help: "Number of request retries, partitioned by status code, verb, and host.",
+		},
+		[]string{"code", "verb", "host"},
+	)
+
+	transportCacheEntries = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "rest_client_transport_cache_entries",
+			Help: "Number of transport entries in the internal cache.",
+		},
+	)
+
+	transportCacheCalls = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "rest_client_transport_create_calls_total",
+			Help: "Number of calls to get a new transport, partitioned by the result of the operation " +
+				"hit: obtained from the cache, miss: created and added to the cache, uncacheable: created and not cached",
+		},
+		[]string{"result"},
+	)
 )
 
 func init() {
@@ -46,26 +124,101 @@ func init() {
 // registerClientMetrics sets up the client latency metrics from client-go.
 func registerClientMetrics() {
 	// register the metrics with our registry
-	Registry.MustRegister(requestResult)
+	Registry.MustRegister(requestResult,
+		requestLatency,
+		resolverLatency,
+		requestSize,
+		responseSize,
+		rateLimiterLatency,
+		requestRetry,
+		transportCacheEntries,
+		transportCacheCalls,
+	)
 
 	// register the metrics with client-go
 	clientmetrics.Register(clientmetrics.RegisterOpts{
-		RequestResult: &resultAdapter{metric: requestResult},
+		RequestResult:         &requestResultAdapter{metric: requestResult},
+		RequestLatency:        &requestLatencyAdapter{metric: requestLatency},
+		ResolverLatency:       &resolverLatencyAdapter{metric: resolverLatency},
+		RequestSize:           &requestSizeAdapter{metric: requestSize},
+		ResponseSize:          &responseSizeAdapter{metric: responseSize},
+		RateLimiterLatency:    &rateLimiterLatencyAdapter{metric: rateLimiterLatency},
+		RequestRetry:          &requestRetryAdapter{metric: requestRetry},
+		TransportCacheEntries: &transportCacheEntriesAdapter{metric: transportCacheEntries},
+		TransportCreateCalls:  &transportCreateCallsAdapter{metric: transportCacheCalls},
 	})
 }
 
-// this section contains adapters, implementations, and other sundry organic, artisanally
-// hand-crafted syntax trees required to convince client-go that it actually wants to let
-// someone use its metrics.
+// Prometheus adapters for client-go metrics hooks.
+
+type requestResultAdapter struct {
+	metric *prometheus.CounterVec
+}
+
+func (r *requestResultAdapter) Increment(_ context.Context, code, method, host string) {
+	r.metric.WithLabelValues(code, method, host).Inc()
+}
+
+type requestLatencyAdapter struct {
+	metric *prometheus.HistogramVec
+}
+
+func (l *requestLatencyAdapter) Observe(_ context.Context, verb string, u url.URL, latency time.Duration) {
+	l.metric.WithLabelValues(verb, u.Host).Observe(latency.Seconds())
+}
+
+type resolverLatencyAdapter struct {
+	metric *prometheus.HistogramVec
+}
+
+func (r *resolverLatencyAdapter) Observe(_ context.Context, host string, latency time.Duration) {
+	r.metric.WithLabelValues(host).Observe(latency.Seconds())
+}
+
+type requestSizeAdapter struct {
+	metric *prometheus.HistogramVec
+}
+
+func (s *requestSizeAdapter) Observe(_ context.Context, verb string, host string, size float64) {
+	s.metric.WithLabelValues(verb, host).Observe(size)
+}
+
+type responseSizeAdapter struct {
+	metric *prometheus.HistogramVec
+}
+
+func (s *responseSizeAdapter) Observe(_ context.Context, verb string, host string, size float64) {
+	s.metric.WithLabelValues(verb, host).Observe(size)
+}
+
+type rateLimiterLatencyAdapter struct {
+	metric *prometheus.HistogramVec
+}
 
-// Client metrics adapters (method #1 for client-go metrics),
-// copied (more-or-less directly) from k8s.io/kubernetes setup code
-// (which isn't anywhere in an easily-importable place).
+func (l *rateLimiterLatencyAdapter) Observe(_ context.Context, verb string, u url.URL, latency time.Duration) {
+	l.metric.WithLabelValues(verb, u.Host).Observe(latency.Seconds())
+}
 
-type resultAdapter struct {
+type requestRetryAdapter struct {
 	metric *prometheus.CounterVec
 }
 
-func (r *resultAdapter) Increment(_ context.Context, code, method, host string) {
+func (r *requestRetryAdapter) IncrementRetry(_ context.Context, code string, method string, host string) {
 	r.metric.WithLabelValues(code, method, host).Inc()
 }
+
+type transportCacheEntriesAdapter struct {
+	metric prometheus.Gauge
+}
+
+func (t *transportCacheEntriesAdapter) Observe(value int) {
+	t.metric.Set(float64(value))
+}
+
+type transportCreateCallsAdapter struct {
+	metric *prometheus.CounterVec
+}
+
+func (t *transportCreateCallsAdapter) Increment(result string) {
+	t.metric.WithLabelValues(result).Inc()
+}

pkg/metrics/client_go_adapter_suite_test.go

@@ -0,0 +1,29 @@
+/*
+Copyright 2025 The Kubernetes 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 metrics
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestClientGoMetrics(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "client-go metric adapters Suite")
+}