Allow show hidden metrics in kube-apiserver

cmd/kube-apiserver/app/BUILD

@@ -64,6 +64,7 @@ go_library(
         "//staging/src/k8s.io/cloud-provider:go_default_library",
         "//staging/src/k8s.io/component-base/cli/flag:go_default_library",
         "//staging/src/k8s.io/component-base/cli/globalflag:go_default_library",
+        "//staging/src/k8s.io/component-base/metrics:go_default_library",
         "//staging/src/k8s.io/component-base/metrics/prometheus/workqueue:go_default_library",
         "//staging/src/k8s.io/component-base/version:go_default_library",
         "//staging/src/k8s.io/component-base/version/verflag:go_default_library",

cmd/kube-apiserver/app/options/BUILD

@@ -33,6 +33,7 @@ go_library(
         "//staging/src/k8s.io/apiserver/pkg/util/feature:go_default_library",
         "//staging/src/k8s.io/component-base/cli/flag:go_default_library",
         "//staging/src/k8s.io/component-base/cli/globalflag:go_default_library",
+        "//staging/src/k8s.io/component-base/metrics:go_default_library",
         "//staging/src/k8s.io/kube-aggregator/pkg/apiserver/scheme:go_default_library",
         "//vendor/github.com/spf13/pflag:go_default_library",
         "//vendor/k8s.io/utils/net:go_default_library",

cmd/kube-apiserver/app/options/options.go

@@ -78,6 +78,8 @@ type ServerRunOptions struct {
 	ServiceAccountSigningKeyFile     string
 	ServiceAccountIssuer             serviceaccount.TokenGenerator
 	ServiceAccountTokenMaxExpiration time.Duration
+
+	ShowHiddenMetricsForVersion string
 }
 
 // NewServerRunOptions creates a new ServerRunOptions object with default parameters
@@ -144,6 +146,15 @@ func (s *ServerRunOptions) Flags() (fss cliflag.NamedFlagSets) {
 	s.EgressSelector.AddFlags(fss.FlagSet("egress selector"))
 	s.Admission.AddFlags(fss.FlagSet("admission"))
 
+	// TODO(RainbowMango): move it to genericoptions before next flag comes.
+	mfs := fss.FlagSet("metrics")
+	mfs.StringVar(&s.ShowHiddenMetricsForVersion, "show-hidden-metrics-for-version", s.ShowHiddenMetricsForVersion,
+		"The previous version for which you want to show hidden metrics. "+
+			"Only the previous minor version is meaningful, other values will not be allowed. "+
+			"The format is <major>.<minor>, e.g.: '1.16'. "+
+			"The purpose of this format is make sure you have the opportunity to notice if the next release hides additional metrics, "+
+			"rather than being surprised when they are permanently removed in the release after that.")
+
 	// Note: the weird ""+ in below lines seems to be the only way to get gofmt to
 	// arrange these text blocks sensibly. Grrr.
 	fs := fss.FlagSet("misc")

cmd/kube-apiserver/app/options/validation.go

@@ -24,6 +24,7 @@ import (
 
 	apiextensionsapiserver "k8s.io/apiextensions-apiserver/pkg/apiserver"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/component-base/metrics"
 	aggregatorscheme "k8s.io/kube-aggregator/pkg/apiserver/scheme"
 	"k8s.io/kubernetes/pkg/api/legacyscheme"
 	"k8s.io/kubernetes/pkg/features"
@@ -143,6 +144,7 @@ func (s *ServerRunOptions) Validate() []error {
 	errs = append(errs, s.InsecureServing.Validate()...)
 	errs = append(errs, s.APIEnablement.Validate(legacyscheme.Scheme, apiextensionsapiserver.Scheme, aggregatorscheme.Scheme)...)
 	errs = append(errs, validateTokenRequest(s)...)
+	errs = append(errs, metrics.ValidateShowHiddenMetricsVersion(s.ShowHiddenMetricsForVersion)...)
 
 	return errs
 }

cmd/kube-apiserver/app/server.go

@@ -58,6 +58,7 @@ import (
 	cloudprovider "k8s.io/cloud-provider"
 	cliflag "k8s.io/component-base/cli/flag"
 	"k8s.io/component-base/cli/globalflag"
+	"k8s.io/component-base/metrics"
 	_ "k8s.io/component-base/metrics/prometheus/workqueue" // for workqueue metric registration
 	"k8s.io/component-base/version"
 	"k8s.io/component-base/version/verflag"
@@ -299,6 +300,10 @@ func CreateKubeAPIServerConfig(
 		PerConnectionBandwidthLimitBytesPerSec: s.MaxConnectionBytesPerSec,
 	})
 
+	if len(s.ShowHiddenMetricsForVersion) > 0 {
+		metrics.SetShowHidden()
+	}
+
 	serviceIPRange, apiServerServiceIP, err := master.ServiceIPRange(s.PrimaryServiceClusterIPRange)
 	if err != nil {
 		return nil, nil, nil, nil, err

staging/src/k8s.io/component-base/metrics/registry.go

@@ -49,6 +49,29 @@ func shouldHide(currentVersion *semver.Version, deprecatedVersion *semver.Versio
 	return false
 }
 
+func validateShowHiddenMetricsVersion(currentVersion semver.Version, targetVersionStr string) error {
+	if targetVersionStr == "" {
+		return nil
+	}
+
+	validVersionStr := fmt.Sprintf("%d.%d", currentVersion.Major, currentVersion.Minor-1)
+	if targetVersionStr != validVersionStr {
+		return fmt.Errorf("--show-hidden-metrics-for-version must be omitted or have the value '%v'. Only the previous minor version is allowed", validVersionStr)
+	}
+
+	return nil
+}
+
+// ValidateShowHiddenMetricsVersion checks invalid version for which show hidden metrics.
+func ValidateShowHiddenMetricsVersion(v string) []error {
+	err := validateShowHiddenMetricsVersion(parseVersion(version.Get()), v)
+	if err != nil {
+		return []error{err}
+	}
+
+	return nil
+}
+
 // SetShowHidden will enable showing hidden metrics. This will no-opt
 // after the initial call
 func SetShowHidden() {

staging/src/k8s.io/component-base/metrics/registry_test.go

@@ -264,3 +264,56 @@ func TestShowHiddenMetric(t *testing.T) {
 	assert.Nil(t, err, "Gather failed %v", err)
 
 }
+
+func TestValidateShowHiddenMetricsVersion(t *testing.T) {
+	currentVersion := parseVersion(apimachineryversion.Info{
+		Major:      "1",
+		Minor:      "17",
+		GitVersion: "v1.17.1-alpha-1.12345",
+	})
+
+	var tests = []struct {
+		desc          string
+		targetVersion string
+		expectedError bool
+	}{
+		{
+			desc:          "invalid version is not allowed",
+			targetVersion: "1.invalid",
+			expectedError: true,
+		},
+		{
+			desc:          "patch version is not allowed",
+			targetVersion: "1.16.0",
+			expectedError: true,
+		},
+		{
+			desc:          "old version is not allowed",
+			targetVersion: "1.15",
+			expectedError: true,
+		},
+		{
+			desc:          "new version is not allowed",
+			targetVersion: "1.17",
+			expectedError: true,
+		},
+		{
+			desc:          "valid version is allowed",
+			targetVersion: "1.16",
+			expectedError: false,
+		},
+	}
+
+	for _, test := range tests {
+		tc := test
+		t.Run(tc.desc, func(t *testing.T) {
+			err := validateShowHiddenMetricsVersion(currentVersion, tc.targetVersion)
+
+			if tc.expectedError {
+				assert.Errorf(t, err, "Failed to test: %s", tc.desc)
+			} else {
+				assert.NoErrorf(t, err, "Failed to test: %s", tc.desc)
+			}
+		})
+	}
+}