Register metrics

New metrics:
- build_info: Build info about descheduler, including Go version, Descheduler version, Git SHA, Git branch
- pods_evicted: Number of successfully evicted pods, by the result, by the strategy, by the namespace

Makefile

@@ -16,11 +16,13 @@
 
 # VERSION is based on a date stamp plus the last commit
 VERSION?=v$(shell date +%Y%m%d)-$(shell git describe --tags --match "v*")
+BRANCH?=$(shell git branch --show-current)
+SHA1?=$(shell git rev-parse HEAD)
 BUILD=$(shell date +%FT%T%z)
 LDFLAG_LOCATION=sigs.k8s.io/descheduler/pkg/version
 ARCHS = amd64 arm64
 
-LDFLAGS=-ldflags "-X ${LDFLAG_LOCATION}.version=${VERSION} -X ${LDFLAG_LOCATION}.buildDate=${BUILD}"
+LDFLAGS=-ldflags "-X ${LDFLAG_LOCATION}.version=${VERSION} -X ${LDFLAG_LOCATION}.buildDate=${BUILD} -X ${LDFLAG_LOCATION}.gitbranch=${BRANCH} -X ${LDFLAG_LOCATION}.gitsha1=${SHA1}"
 
 GOLANGCI_VERSION := v1.30.0
 HAS_GOLANGCI := $(shell ls _output/bin/golangci-lint)

metrics/metrics.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2021 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 (
+	"sync"
+
+	"k8s.io/component-base/metrics"
+	"k8s.io/component-base/metrics/legacyregistry"
+	"sigs.k8s.io/descheduler/pkg/version"
+)
+
+const (
+	// DeschedulerSubsystem - subsystem name used by descheduler
+	DeschedulerSubsystem = "descheduler"
+)
+
+var (
+	PodsEvicted = metrics.NewCounterVec(
+		&metrics.CounterOpts{
+			Subsystem:      DeschedulerSubsystem,
+			Name:           "pods_evicted",
+			Help:           "Number of evicted pods, by the result, by the strategy, by the namespace. 'failed' result means a pod could not be evicted",
+			StabilityLevel: metrics.ALPHA,
+		}, []string{"result", "strategy", "namespace"})
+
+	buildInfo = metrics.NewGauge(
+		&metrics.GaugeOpts{
+			Subsystem:      DeschedulerSubsystem,
+			Name:           "build_info",
+			Help:           "Build info about descheduler, including Go version, Descheduler version, Git SHA, Git branch",
+			ConstLabels:    map[string]string{"GoVersion": version.Get().GoVersion, "DeschedulerVersion": version.Get().GitVersion, "GitBranch": version.Get().GitBranch, "GitSha1": version.Get().GitSha1},
+			StabilityLevel: metrics.ALPHA,
+		},
+	)
+
+	metricsList = []metrics.Registerable{
+		PodsEvicted,
+		buildInfo,
+	}
+)
+
+var registerMetrics sync.Once
+
+// Register all metrics.
+func Register() {
+	// Register the metrics.
+	registerMetrics.Do(func() {
+		RegisterMetrics(metricsList...)
+	})
+}
+
+// RegisterMetrics registers a list of metrics.
+func RegisterMetrics(extraMetrics ...metrics.Registerable) {
+	for _, metric := range extraMetrics {
+		legacyregistry.MustRegister(metric)
+	}
+}

pkg/descheduler/descheduler.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/client-go/informers"
 	"sigs.k8s.io/descheduler/cmd/descheduler/app/options"
+	"sigs.k8s.io/descheduler/metrics"
 	"sigs.k8s.io/descheduler/pkg/api"
 	"sigs.k8s.io/descheduler/pkg/descheduler/client"
 	"sigs.k8s.io/descheduler/pkg/descheduler/evictions"
@@ -36,6 +37,8 @@ import (
 )
 
 func Run(rs *options.DeschedulerServer) error {
+	metrics.Register()
+
 	ctx := context.Background()
 	rsclient, err := client.CreateClient(rs.KubeconfigFile)
 	if err != nil {

pkg/version/version.go

@@ -30,6 +30,12 @@ var (
 	// buildDate in ISO8601 format, output of $(date -u +'%Y-%m-%dT%H:%M:%SZ')
 	// It should be set during build via -ldflags.
 	buildDate string
+	// gitbranch is a constant representing git branch for this build.
+	// It should be set during build via -ldflags.
+	gitbranch string
+	// gitbranch is a constant representing git sha1 for this build.
+	// It should be set during build via -ldflags.
+	gitsha1 string
 )
 
 // Info holds the information related to descheduler app version.
@@ -37,6 +43,8 @@ type Info struct {
 	Major      string `json:"major"`
 	Minor      string `json:"minor"`
 	GitVersion string `json:"gitVersion"`
+	GitBranch  string `json:"gitBranch"`
+	GitSha1    string `json:"gitSha1"`
 	BuildDate  string `json:"buildDate"`
 	GoVersion  string `json:"goVersion"`
 	Compiler   string `json:"compiler"`
@@ -51,6 +59,8 @@ func Get() Info {
 		Major:      majorVersion,
 		Minor:      minorVersion,
 		GitVersion: version,
+		GitBranch:  gitbranch,
+		GitSha1:    gitsha1,
 		BuildDate:  buildDate,
 		GoVersion:  runtime.Version(),
 		Compiler:   runtime.Compiler,