Add info metric for client-go version

KSM supports a range of Kubernetes versions which makes it important to
keep up with new versions as clusters upgrade.

In order to allow for alerting on unsupported cluster versions, this commit
adds an info metric for the client-go version used by KSM. This way users can
set up alerts if the cluster in which KSM is running is outside of the supported range.

Signed-off-by: fpetkovski <filip.petkovsky@gmail.com>

Author: fpetkovski

Makefile

@@ -20,10 +20,12 @@ MULTI_ARCH_IMG = $(IMAGE)-$(ARCH)
 USER ?= $(shell id -u -n)
 HOST ?= $(shell hostname)
 MARKDOWNLINT_CLI2_VERSION = 0.18.1
+CLIENT_GO_VERSION = $(shell go list -m -f '{{.Version}}' k8s.io/client-go)
+KSM_MODULE = $(shell go list -m)
 
 DOCKER_CLI ?= docker
 PROMTOOL_CLI ?= promtool
-GOMPLATE_CLI ?= go tool github.com/hairyhenderson/gomplate/v4/cmd/gomplate 
+GOMPLATE_CLI ?= go tool github.com/hairyhenderson/gomplate/v4/cmd/gomplate
 GOJSONTOYAML_CLI ?= go tool github.com/brancz/gojsontoyaml
 EMBEDMD_CLI ?= go tool github.com/campoy/embedmd
 JSONNET_CLI ?= go tool github.com/google/go-jsonnet/cmd/jsonnet
@@ -69,7 +71,7 @@ doccheck: generate validate-template
 	@echo OK
 
 build-local:
-	GOOS=$(OS) GOARCH=$(ARCH) CGO_ENABLED=0 go build -ldflags "-s -w -X ${PKG}/version.Version=${TAG} -X ${PKG}/version.Revision=${GIT_COMMIT} -X ${PKG}/version.Branch=${BRANCH} -X ${PKG}/version.BuildUser=${USER}@${HOST} -X ${PKG}/version.BuildDate=${BUILD_DATE}" -o kube-state-metrics
+	GOOS=$(OS) GOARCH=$(ARCH) CGO_ENABLED=0 go build -ldflags "-s -w -X ${PKG}/version.Version=${TAG} -X ${PKG}/version.Revision=${GIT_COMMIT} -X ${PKG}/version.Branch=${BRANCH} -X ${PKG}/version.BuildUser=${USER}@${HOST} -X ${PKG}/version.BuildDate=${BUILD_DATE} -X ${PKG}/version.BuildDate=${BUILD_DATE} -X ${KSM_MODULE}/pkg/app.ClientGoVersion=${CLIENT_GO_VERSION}" -o kube-state-metrics
 
 build: kube-state-metrics
 

pkg/app/server.go

@@ -63,6 +63,10 @@ import (
 	"k8s.io/kube-state-metrics/v2/pkg/util/proc"
 )
 
+// ClientGoVersion is the version for the client-go library used by KSM. This
+// value is set at build time using go build flags.
+var ClientGoVersion = "unknown"
+
 const (
 	metricsPath = "/metrics"
 	healthzPath = "/healthz"
@@ -86,6 +90,16 @@ func RunKubeStateMetricsWrapper(ctx context.Context, opts *options.Options) erro
 func RunKubeStateMetrics(ctx context.Context, opts *options.Options) error {
 	ksmMetricsRegistry := prometheus.NewRegistry()
 	ksmMetricsRegistry.MustRegister(versionCollector.NewCollector("kube_state_metrics"))
+
+	clientGoVersion := promauto.With(ksmMetricsRegistry).NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "kube_state_metrics_client_go_info",
+			Help: "An info metric for the client-go version used by kube-state-metrics",
+		},
+		[]string{"version"},
+	)
+	clientGoVersion.WithLabelValues(ClientGoVersion).Set(1)
+
 	durationVec := promauto.With(ksmMetricsRegistry).NewHistogramVec(
 		prometheus.HistogramOpts{
 			Name:        "http_request_duration_seconds",