Define EvictionsInBackground feature gate

cmd/descheduler/app/options/options.go

@@ -18,6 +18,7 @@ limitations under the License.
 package options
 
 import (
+	"strings"
 	"time"
 
 	"github.com/spf13/pflag"
@@ -25,14 +26,18 @@ import (
 	apiserver "k8s.io/apiserver/pkg/server"
 	apiserveroptions "k8s.io/apiserver/pkg/server/options"
 	clientset "k8s.io/client-go/kubernetes"
+
 	restclient "k8s.io/client-go/rest"
+	cliflag "k8s.io/component-base/cli/flag"
 	componentbaseconfig "k8s.io/component-base/config"
 	componentbaseoptions "k8s.io/component-base/config/options"
+	"k8s.io/component-base/featuregate"
 	"k8s.io/klog/v2"
 
 	"sigs.k8s.io/descheduler/pkg/apis/componentconfig"
 	"sigs.k8s.io/descheduler/pkg/apis/componentconfig/v1alpha1"
 	deschedulerscheme "sigs.k8s.io/descheduler/pkg/descheduler/scheme"
+	"sigs.k8s.io/descheduler/pkg/features"
 	"sigs.k8s.io/descheduler/pkg/tracing"
 )
 
@@ -50,6 +55,10 @@ type DeschedulerServer struct {
 	SecureServingInfo *apiserver.SecureServingInfo
 	DisableMetrics    bool
 	EnableHTTP2       bool
+	// FeatureGates enabled by the user
+	FeatureGates map[string]bool
+	// DefaultFeatureGates for internal accessing so unit tests can enable/disable specific features
+	DefaultFeatureGates featuregate.FeatureGate
 }
 
 // NewDeschedulerServer creates a new DeschedulerServer with default parameters
@@ -107,6 +116,8 @@ func (rs *DeschedulerServer) AddFlags(fs *pflag.FlagSet) {
 	fs.Float64Var(&rs.Tracing.SampleRate, "otel-sample-rate", 1.0, "Sample rate to collect the Traces")
 	fs.BoolVar(&rs.Tracing.FallbackToNoOpProviderOnError, "otel-fallback-no-op-on-error", false, "Fallback to NoOp Tracer in case of error")
 	fs.BoolVar(&rs.EnableHTTP2, "enable-http2", false, "If http/2 should be enabled for the metrics and health check")
+	fs.Var(cliflag.NewMapStringBool(&rs.FeatureGates), "feature-gates", "A set of key=value pairs that describe feature gates for alpha/experimental features. "+
+		"Options are:\n"+strings.Join(features.DefaultMutableFeatureGate.KnownFeatures(), "\n"))
 
 	componentbaseoptions.BindLeaderElectionFlags(&rs.LeaderElection, fs)
 
@@ -114,6 +125,12 @@ func (rs *DeschedulerServer) AddFlags(fs *pflag.FlagSet) {
 }
 
 func (rs *DeschedulerServer) Apply() error {
+	err := features.DefaultMutableFeatureGate.SetFromMap(rs.FeatureGates)
+	if err != nil {
+		return err
+	}
+	rs.DefaultFeatureGates = features.DefaultMutableFeatureGate
+
 	// loopbackClientConfig is a config for a privileged loopback connection
 	var loopbackClientConfig *restclient.Config
 	var secureServing *apiserver.SecureServingInfo

cmd/descheduler/app/server.go

@@ -23,16 +23,15 @@ import (
 	"os/signal"
 	"syscall"
 
-	"k8s.io/apiserver/pkg/server/healthz"
+	"github.com/spf13/cobra"
 
 	"sigs.k8s.io/descheduler/cmd/descheduler/app/options"
 	"sigs.k8s.io/descheduler/pkg/descheduler"
 	"sigs.k8s.io/descheduler/pkg/tracing"
 
-	"github.com/spf13/cobra"
-
 	"k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apimachinery/pkg/watch"
+	"k8s.io/apiserver/pkg/server/healthz"
 	"k8s.io/apiserver/pkg/server/mux"
 	"k8s.io/component-base/featuregate"
 	"k8s.io/component-base/logs"

docs/cli/descheduler.md

@@ -23,6 +23,10 @@ descheduler [flags]
       --disable-metrics                          Disables metrics. The metrics are by default served through https://localhost:10258/metrics. Secure address, resp. port can be changed through --bind-address, resp. --secure-port flags.
       --dry-run                                  Execute descheduler in dry run mode.
       --enable-http2                             If http/2 should be enabled for the metrics and health check
+      --feature-gates mapStringBool              A set of key=value pairs that describe feature gates for alpha/experimental features. Options are:
+                                                 AllAlpha=true|false (ALPHA - default=false)
+                                                 AllBeta=true|false (BETA - default=false)
+                                                 EvictionsInBackground=true|false (ALPHA - default=false)
   -h, --help                                     help for descheduler
       --http2-max-streams-per-connection int     The limit that the server gives to clients for the maximum number of streams in an HTTP/2 connection. Zero means to use golang's default.
       --kubeconfig string                        File with kube configuration. Deprecated, use client-connection-kubeconfig instead.

pkg/features/features.go

@@ -0,0 +1,49 @@
+package features
+
+import (
+	"k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/component-base/featuregate"
+)
+
+const (
+	// Every feature gate should add method here following this template:
+	//
+	// // owner: @username
+	// // kep: kep link
+	// // alpha: v1.X
+	// MyFeature featuregate.Feature = "MyFeature"
+	//
+	// Feature gates should be listed in alphabetical, case-sensitive
+	// (upper before any lower case character) order. This reduces the risk
+	// of code conflicts because changes are more likely to be scattered
+	// across the file.
+
+	// owner: @ingvagabund
+	// kep: https://github.com/kubernetes-sigs/descheduler/issues/1397
+	// alpha: v1.31
+	//
+	// Enable evictions in background so users can create their own eviction policies
+	// as an alternative to immediate evictions.
+	EvictionsInBackground featuregate.Feature = "EvictionsInBackground"
+)
+
+func init() {
+	runtime.Must(DefaultMutableFeatureGate.Add(defaultDeschedulerFeatureGates))
+}
+
+// defaultDeschedulerFeatureGates consists of all known descheduler-specific feature keys.
+// To add a new feature, define a key for it above and add it here. The features will be
+// available throughout descheduler binary.
+//
+// Entries are separated from each other with blank lines to avoid sweeping gofmt changes
+// when adding or removing one entry.
+var defaultDeschedulerFeatureGates = map[featuregate.Feature]featuregate.FeatureSpec{
+	EvictionsInBackground: {Default: false, PreRelease: featuregate.Alpha},
+}
+
+// DefaultMutableFeatureGate is a mutable version of DefaultFeatureGate.
+// Only top-level commands/options setup and the k8s.io/component-base/featuregate/testing package should make use of this.
+// Tests that need to modify feature gates for the duration of their test should use:
+//
+//	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.<FeatureName>, <value>)()
+var DefaultMutableFeatureGate featuregate.MutableFeatureGate = featuregate.NewFeatureGate()