refactor admission flag: add two admission flags and make plugins auto in recommended order

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

@@ -46,7 +46,7 @@ type ServerRunOptions struct {
 	InsecureServing         *kubeoptions.InsecureServingOptions
 	Audit                   *genericoptions.AuditOptions
 	Features                *genericoptions.FeatureOptions
-	Admission               *genericoptions.AdmissionOptions
+	Admission               *kubeoptions.AdmissionOptions
 	Authentication          *kubeoptions.BuiltInAuthenticationOptions
 	Authorization           *kubeoptions.BuiltInAuthorizationOptions
 	CloudProvider           *kubeoptions.CloudProviderOptions
@@ -82,7 +82,7 @@ func NewServerRunOptions() *ServerRunOptions {
 		InsecureServing:      kubeoptions.NewInsecureServingOptions(),
 		Audit:                genericoptions.NewAuditOptions(),
 		Features:             genericoptions.NewFeatureOptions(),
-		Admission:            genericoptions.NewAdmissionOptions(),
+		Admission:            kubeoptions.NewAdmissionOptions(),
 		Authentication:       kubeoptions.NewBuiltInAuthenticationOptions().WithAll(),
 		Authorization:        kubeoptions.NewBuiltInAuthorizationOptions(),
 		CloudProvider:        kubeoptions.NewCloudProviderOptions(),
@@ -116,10 +116,6 @@ func NewServerRunOptions() *ServerRunOptions {
 	// Overwrite the default for storage data format.
 	s.Etcd.DefaultStorageMediaType = "application/vnd.kubernetes.protobuf"
 
-	// register all admission plugins
-	RegisterAllAdmissionPlugins(s.Admission.Plugins)
-	// Set the default for admission plugins names
-	s.Admission.PluginNames = []string{"AlwaysAdmit"}
 	return &s
 }
 

pkg/kubeapiserver/options/admission.go

+/*
+Copyright 2018 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 options
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/spf13/pflag"
+
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apiserver/pkg/admission"
+	"k8s.io/apiserver/pkg/server"
+	genericoptions "k8s.io/apiserver/pkg/server/options"
+	"k8s.io/client-go/informers"
+	"k8s.io/client-go/rest"
+)
+
+// AdmissionOptions holds the admission options.
+// It is a wrap of generic AdmissionOptions.
+type AdmissionOptions struct {
+	// GenericAdmission holds the generic admission options.
+	GenericAdmission *genericoptions.AdmissionOptions
+	// DEPRECATED flag, should use EnabledAdmissionPlugins and DisabledAdmissionPlugins.
+	// They are mutually exclusive, specify both will lead to an error.
+	PluginNames []string
+}
+
+// NewAdmissionOptions creates a new instance of AdmissionOptions
+// Note:
+//  In addition it calls RegisterAllAdmissionPlugins to register
+//  all kube-apiserver admission plugins.
+//
+//  Provides the list of RecommendedPluginOrder that holds sane values
+//  that can be used by servers that don't care about admission chain.
+//  Servers that do care can overwrite/append that field after creation.
+func NewAdmissionOptions() *AdmissionOptions {
+	options := genericoptions.NewAdmissionOptions()
+	// register all admission plugins
+	RegisterAllAdmissionPlugins(options.Plugins)
+	// set RecommendedPluginOrder
+	options.RecommendedPluginOrder = AllOrderedPlugins
+	// set DefaultOffPlugins
+	options.DefaultOffPlugins = DefaultOffAdmissionPlugins()
+
+	return &AdmissionOptions{
+		GenericAdmission: options,
+	}
+}
+
+// AddFlags adds flags related to admission for kube-apiserver to the specified FlagSet
+func (a *AdmissionOptions) AddFlags(fs *pflag.FlagSet) {
+	fs.StringSliceVar(&a.PluginNames, "admission-control", a.PluginNames, ""+
+		"Admission is divided into two phases. "+
+		"In the first phase, only mutating admission plugins run. "+
+		"In the second phase, only validating admission plugins run. "+
+		"The names in the below list may represent a validating plugin, a mutating plugin, or both. "+
+		"The order of plugins in which they are passed to this flag does not matter. "+
+		"Comma-delimited list of: "+strings.Join(a.GenericAdmission.Plugins.Registered(), ", ")+".")
+	fs.MarkDeprecated("admission-control", "Use --enable-admission-plugins or --disable-admission-plugins instead. Will be removed in a future version.")
+
+	a.GenericAdmission.AddFlags(fs)
+}
+
+// Validate verifies flags passed to kube-apiserver AdmissionOptions.
+// Kube-apiserver verifies PluginNames and then call generic AdmissionOptions.Validate.
+func (a *AdmissionOptions) Validate() []error {
+	if a == nil {
+		return nil
+	}
+	errs := []error{}
+	if a.PluginNames != nil &&
+		(a.GenericAdmission.EnablePlugins != nil || a.GenericAdmission.DisablePlugins != nil) {
+		errs = append(errs, fmt.Errorf("admission-control and enable-admission-plugins/disable-admission-plugins flags are mutually exclusive"))
+	}
+
+	registeredPlugins := sets.NewString(a.GenericAdmission.Plugins.Registered()...)
+	for _, name := range a.PluginNames {
+		if !registeredPlugins.Has(name) {
+			errs = append(errs, fmt.Errorf("admission-control plugin %q is unknown", name))
+		}
+	}
+
+	errs = append(errs, a.GenericAdmission.Validate()...)
+
+	return errs
+}
+
+// ApplyTo adds the admission chain to the server configuration.
+// Kube-apiserver just call generic AdmissionOptions.ApplyTo.
+func (a *AdmissionOptions) ApplyTo(
+	c *server.Config,
+	informers informers.SharedInformerFactory,
+	kubeAPIServerClientConfig *rest.Config,
+	scheme *runtime.Scheme,
+	pluginInitializers ...admission.PluginInitializer,
+) error {
+	if a == nil {
+		return nil
+	}
+
+	if a.PluginNames != nil {
+		// pass PluginNames to generic AdmissionOptions
+		a.GenericAdmission.EnablePlugins = a.PluginNames
+	}
+
+	return a.GenericAdmission.ApplyTo(c, informers, kubeAPIServerClientConfig, scheme, pluginInitializers...)
+}

cmd/kube-apiserver/app/options/plugins.go → pkg/kubeapiserver/options/plugins.go

@@ -24,7 +24,6 @@ import (
 	_ "k8s.io/kubernetes/pkg/cloudprovider/providers"
 
 	// Admission policies
-	"k8s.io/apiserver/pkg/admission"
 	"k8s.io/kubernetes/plugin/pkg/admission/admit"
 	"k8s.io/kubernetes/plugin/pkg/admission/alwayspullimages"
 	"k8s.io/kubernetes/plugin/pkg/admission/antiaffinity"
@@ -52,15 +51,59 @@ import (
 	"k8s.io/kubernetes/plugin/pkg/admission/securitycontext/scdeny"
 	"k8s.io/kubernetes/plugin/pkg/admission/serviceaccount"
 	"k8s.io/kubernetes/plugin/pkg/admission/storageclass/setdefault"
+
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apiserver/pkg/admission"
+	"k8s.io/apiserver/pkg/admission/plugin/initialization"
+	"k8s.io/apiserver/pkg/admission/plugin/namespace/lifecycle"
+	mutatingwebhook "k8s.io/apiserver/pkg/admission/plugin/webhook/mutating"
+	validatingwebhook "k8s.io/apiserver/pkg/admission/plugin/webhook/validating"
 )
 
-// RegisterAllAdmissionPlugins registers all admission plugins
+// AllOrderedPlugins is the list of all the plugins in order.
+var AllOrderedPlugins = []string{
+	admit.PluginName,                      // AlwaysAdmit
+	autoprovision.PluginName,              // NamespaceAutoProvision
+	lifecycle.PluginName,                  // NamespaceLifecycle
+	exists.PluginName,                     // NamespaceExists
+	scdeny.PluginName,                     // SecurityContextDeny
+	antiaffinity.PluginName,               // LimitPodHardAntiAffinity
+	initialresources.PluginName,           // InitialResources
+	podpreset.PluginName,                  // PodPreset
+	limitranger.PluginName,                // LimitRanger
+	serviceaccount.PluginName,             // ServiceAccount
+	noderestriction.PluginName,            // NodeRestriction
+	alwayspullimages.PluginName,           // AlwaysPullImages
+	imagepolicy.PluginName,                // ImagePolicyWebhook
+	podsecuritypolicy.PluginName,          // PodSecurityPolicy
+	podnodeselector.PluginName,            // PodNodeSelector
+	podpriority.PluginName,                // Priority
+	defaulttolerationseconds.PluginName,   // DefaultTolerationSeconds
+	podtolerationrestriction.PluginName,   // PodTolerationRestriction
+	exec.DenyEscalatingExec,               // DenyEscalatingExec
+	exec.DenyExecOnPrivileged,             // DenyExecOnPrivileged
+	eventratelimit.PluginName,             // EventRateLimit
+	extendedresourcetoleration.PluginName, // ExtendedResourceToleration
+	label.PluginName,                      // PersistentVolumeLabel
+	setdefault.PluginName,                 // DefaultStorageClass
+	pvcprotection.PluginName,              // PVCProtection
+	gc.PluginName,                         // OwnerReferencesPermissionEnforcement
+	resize.PluginName,                     // PersistentVolumeClaimResize
+	mutatingwebhook.PluginName,            // MutatingAdmissionWebhook
+	initialization.PluginName,             // Initializers
+	validatingwebhook.PluginName,          // ValidatingAdmissionWebhook
+	resourcequota.PluginName,              // ResourceQuota
+	deny.PluginName,                       // AlwaysDeny
+}
+
+// RegisterAllAdmissionPlugins registers all admission plugins and
+// sets the recommended plugins order.
 func RegisterAllAdmissionPlugins(plugins *admission.Plugins) {
-	admit.Register(plugins)
+	admit.Register(plugins) // DEPRECATED as no real meaning
 	alwayspullimages.Register(plugins)
 	antiaffinity.Register(plugins)
 	defaulttolerationseconds.Register(plugins)
-	deny.Register(plugins)
+	deny.Register(plugins) // DEPRECATED as no real meaning
 	eventratelimit.Register(plugins)
 	exec.Register(plugins)
 	extendedresourcetoleration.Register(plugins)
@@ -84,3 +127,11 @@ func RegisterAllAdmissionPlugins(plugins *admission.Plugins) {
 	resize.Register(plugins)
 	pvcprotection.Register(plugins)
 }
+
+// DefaultOffAdmissionPlugins get admission plugins off by default for kube-apiserver.
+func DefaultOffAdmissionPlugins() sets.String {
+	defaultOffPlugins := sets.NewString(AllOrderedPlugins...)
+	defaultOffPlugins.Delete(lifecycle.PluginName)
+
+	return defaultOffPlugins
+}

plugin/pkg/admission/admit/admission.go

@@ -19,40 +19,46 @@ package admit
 import (
 	"io"
 
+	"github.com/golang/glog"
 	"k8s.io/apiserver/pkg/admission"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "AlwaysAdmit"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("AlwaysAdmit", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewAlwaysAdmit(), nil
 	})
 }
 
-// AlwaysAdmit is an implementation of admission.Interface which always says yes to an admit request.
-// It is useful in tests and when using kubernetes in an open manner.
-type AlwaysAdmit struct{}
+// alwaysAdmit is an implementation of admission.Interface which always says yes to an admit request.
+type alwaysAdmit struct{}
 
-var _ admission.MutationInterface = AlwaysAdmit{}
-var _ admission.ValidationInterface = AlwaysAdmit{}
+var _ admission.MutationInterface = alwaysAdmit{}
+var _ admission.ValidationInterface = alwaysAdmit{}
 
 // Admit makes an admission decision based on the request attributes
-func (AlwaysAdmit) Admit(a admission.Attributes) (err error) {
+func (alwaysAdmit) Admit(a admission.Attributes) (err error) {
 	return nil
 }
 
 // Validate makes an admission decision based on the request attributes.  It is NOT allowed to mutate.
-func (AlwaysAdmit) Validate(a admission.Attributes) (err error) {
+func (alwaysAdmit) Validate(a admission.Attributes) (err error) {
 	return nil
 }
 
 // Handles returns true if this admission controller can handle the given operation
 // where operation can be one of CREATE, UPDATE, DELETE, or CONNECT
-func (AlwaysAdmit) Handles(operation admission.Operation) bool {
+func (alwaysAdmit) Handles(operation admission.Operation) bool {
 	return true
 }
 
 // NewAlwaysAdmit creates a new always admit admission handler
-func NewAlwaysAdmit() *AlwaysAdmit {
-	return new(AlwaysAdmit)
+func NewAlwaysAdmit() admission.Interface {
+	// DEPRECATED: AlwaysAdmit admit all admission request, it is no use.
+	glog.Warningf("%s admission controller is deprecated. "+
+		"Please remove this controller from your configuration files and scripts.", PluginName)
+	return new(alwaysAdmit)
 }

plugin/pkg/admission/admit/admission_test.go

@@ -25,7 +25,7 @@ import (
 
 func TestAdmissionNonNilAttribute(t *testing.T) {
 	handler := NewAlwaysAdmit()
-	err := handler.Admit(admission.NewAttributesRecord(nil, nil, api.Kind("kind").WithVersion("version"), "namespace", "name", api.Resource("resource").WithVersion("version"), "subresource", admission.Create, nil))
+	err := handler.(*alwaysAdmit).Admit(admission.NewAttributesRecord(nil, nil, api.Kind("kind").WithVersion("version"), "namespace", "name", api.Resource("resource").WithVersion("version"), "subresource", admission.Create, nil))
 	if err != nil {
 		t.Errorf("Unexpected error returned from admission handler")
 	}
@@ -33,7 +33,7 @@ func TestAdmissionNonNilAttribute(t *testing.T) {
 
 func TestAdmissionNilAttribute(t *testing.T) {
 	handler := NewAlwaysAdmit()
-	err := handler.Admit(nil)
+	err := handler.(*alwaysAdmit).Admit(nil)
 	if err != nil {
 		t.Errorf("Unexpected error returned from admission handler")
 	}

plugin/pkg/admission/alwayspullimages/admission.go

@@ -33,9 +33,12 @@ import (
 	api "k8s.io/kubernetes/pkg/apis/core"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "AlwaysPullImages"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("AlwaysPullImages", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewAlwaysPullImages(), nil
 	})
 }

plugin/pkg/admission/antiaffinity/admission.go

@@ -26,9 +26,11 @@ import (
 	kubeletapis "k8s.io/kubernetes/pkg/kubelet/apis"
 )
 
+const PluginName = "LimitPodHardAntiAffinity"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("LimitPodHardAntiAffinityTopology", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewInterPodAntiAffinity(), nil
 	})
 }

plugin/pkg/admission/defaulttolerationseconds/admission.go

@@ -28,6 +28,9 @@ import (
 	"k8s.io/kubernetes/pkg/scheduler/algorithm"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "DefaultTolerationSeconds"
+
 var (
 	defaultNotReadyTolerationSeconds = flag.Int64("default-not-ready-toleration-seconds", 300,
 		"Indicates the tolerationSeconds of the toleration for notReady:NoExecute"+
@@ -40,7 +43,7 @@ var (
 
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("DefaultTolerationSeconds", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewDefaultTolerationSeconds(), nil
 	})
 }

plugin/pkg/admission/deny/admission.go

@@ -20,40 +20,47 @@ import (
 	"errors"
 	"io"
 
+	"github.com/golang/glog"
+
 	"k8s.io/apiserver/pkg/admission"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "AlwaysDeny"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("AlwaysDeny", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewAlwaysDeny(), nil
 	})
 }
 
-// AlwaysDeny is an implementation of admission.Interface which always says no to an admission request.
-// It is useful in unit tests to force an operation to be forbidden.
-type AlwaysDeny struct{}
+// alwaysDeny is an implementation of admission.Interface which always says no to an admission request.
+type alwaysDeny struct{}
 
-var _ admission.MutationInterface = AlwaysDeny{}
-var _ admission.ValidationInterface = AlwaysDeny{}
+var _ admission.MutationInterface = alwaysDeny{}
+var _ admission.ValidationInterface = alwaysDeny{}
 
 // Admit makes an admission decision based on the request attributes.
-func (AlwaysDeny) Admit(a admission.Attributes) (err error) {
-	return admission.NewForbidden(a, errors.New("Admission control is denying all modifications"))
+func (alwaysDeny) Admit(a admission.Attributes) (err error) {
+	return admission.NewForbidden(a, errors.New("admission control is denying all modifications"))
 }
 
 // Validate makes an admission decision based on the request attributes.  It is NOT allowed to mutate.
-func (AlwaysDeny) Validate(a admission.Attributes) (err error) {
-	return admission.NewForbidden(a, errors.New("Admission control is denying all modifications"))
+func (alwaysDeny) Validate(a admission.Attributes) (err error) {
+	return admission.NewForbidden(a, errors.New("admission control is denying all modifications"))
 }
 
 // Handles returns true if this admission controller can handle the given operation
 // where operation can be one of CREATE, UPDATE, DELETE, or CONNECT
-func (AlwaysDeny) Handles(operation admission.Operation) bool {
+func (alwaysDeny) Handles(operation admission.Operation) bool {
 	return true
 }
 
 // NewAlwaysDeny creates an always deny admission handler
-func NewAlwaysDeny() *AlwaysDeny {
-	return new(AlwaysDeny)
+func NewAlwaysDeny() admission.Interface {
+	// DEPRECATED: AlwaysDeny denys all admission request, it is no use.
+	glog.Warningf("%s admission controller is deprecated. "+
+		"Please remove this controller from your configuration files and scripts.", PluginName)
+	return new(alwaysDeny)
 }

plugin/pkg/admission/deny/admission_test.go

@@ -25,7 +25,7 @@ import (
 
 func TestAdmission(t *testing.T) {
 	handler := NewAlwaysDeny()
-	err := handler.Admit(admission.NewAttributesRecord(nil, nil, api.Kind("kind").WithVersion("version"), "namespace", "name", api.Resource("resource").WithVersion("version"), "subresource", admission.Create, nil))
+	err := handler.(*alwaysDeny).Admit(admission.NewAttributesRecord(nil, nil, api.Kind("kind").WithVersion("version"), "namespace", "name", api.Resource("resource").WithVersion("version"), "subresource", admission.Create, nil))
 	if err == nil {
 		t.Error("Expected error returned from admission handler")
 	}

plugin/pkg/admission/eventratelimit/admission.go

@@ -26,9 +26,12 @@ import (
 	"k8s.io/kubernetes/plugin/pkg/admission/eventratelimit/apis/eventratelimit/validation"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "EventRateLimit"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("EventRateLimit",
+	plugins.Register(PluginName,
 		func(config io.Reader) (admission.Interface, error) {
 			// load the configuration provided (if any)
 			configuration, err := LoadConfiguration(config)

plugin/pkg/admission/exec/admission.go

@@ -29,15 +29,23 @@ import (
 	kubeapiserveradmission "k8s.io/kubernetes/pkg/kubeapiserver/admission"
 )
 
+const (
+	// DenyEscalatingExec indicates name of admission plugin.
+	DenyEscalatingExec = "DenyEscalatingExec"
+	// DenyExecOnPrivileged indicates name of admission plugin.
+	// Deprecated, should use DenyEscalatingExec instead.
+	DenyExecOnPrivileged = "DenyExecOnPrivileged"
+)
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("DenyEscalatingExec", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(DenyEscalatingExec, func(config io.Reader) (admission.Interface, error) {
 		return NewDenyEscalatingExec(), nil
 	})
 
 	// This is for legacy support of the DenyExecOnPrivileged admission controller.  Most
 	// of the time DenyEscalatingExec should be preferred.
-	plugins.Register("DenyExecOnPrivileged", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(DenyExecOnPrivileged, func(config io.Reader) (admission.Interface, error) {
 		return NewDenyExecOnPrivileged(), nil
 	})
 }

plugin/pkg/admission/extendedresourcetoleration/admission.go

@@ -27,9 +27,12 @@ import (
 	"k8s.io/kubernetes/pkg/apis/core/helper"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "ExtendedResourceToleration"
+
 // Register is called by the apiserver to register the plugin factory.
 func Register(plugins *admission.Plugins) {
-	plugins.Register("ExtendedResourceToleration", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return newExtendedResourceToleration(), nil
 	})
 }

plugin/pkg/admission/gc/gc_admission.go

@@ -30,9 +30,12 @@ import (
 	"k8s.io/apiserver/pkg/authorization/authorizer"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "OwnerReferencesPermissionEnforcement"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("OwnerReferencesPermissionEnforcement", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		// the pods/status endpoint is ignored by this plugin since old kubelets
 		// corrupt them.  the pod status strategy ensures status updates cannot mutate
 		// ownerRef.

plugin/pkg/admission/imagepolicy/admission.go

@@ -43,13 +43,16 @@ import (
 	_ "k8s.io/kubernetes/pkg/apis/imagepolicy/install"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "ImagePolicyWebhook"
+
 var (
 	groupVersions = []schema.GroupVersion{v1alpha1.SchemeGroupVersion}
 )
 
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("ImagePolicyWebhook", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		newImagePolicyWebhook, err := NewImagePolicyWebhook(config)
 		if err != nil {
 			return nil, err

plugin/pkg/admission/initialresources/admission.go

@@ -42,12 +42,14 @@ const (
 	samplesThreshold           = 30
 	week                       = 7 * 24 * time.Hour
 	month                      = 30 * 24 * time.Hour
+	// PluginName indicates name of admission plugin.
+	PluginName = "InitialResources"
 )
 
 // Register registers a plugin
 // WARNING: this feature is experimental and will definitely change.
 func Register(plugins *admission.Plugins) {
-	plugins.Register("InitialResources", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		// TODO: remove the usage of flags in favor of reading versioned configuration
 		s, err := newDataSource(*source)
 		if err != nil {

plugin/pkg/admission/limitranger/admission.go

@@ -41,11 +41,13 @@ import (
 
 const (
 	limitRangerAnnotation = "kubernetes.io/limit-ranger"
+	// PluginName indicates name of admission plugin.
+	PluginName = "LimitRanger"
 )
 
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("LimitRanger", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewLimitRanger(&DefaultLimitRangerActions{})
 	})
 }

plugin/pkg/admission/namespace/autoprovision/admission.go

@@ -30,9 +30,12 @@ import (
 	kubeapiserveradmission "k8s.io/kubernetes/pkg/kubeapiserver/admission"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "NamespaceAutoProvision"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("NamespaceAutoProvision", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewProvision(), nil
 	})
 }

plugin/pkg/admission/namespace/exists/admission.go

@@ -30,9 +30,12 @@ import (
 	kubeapiserveradmission "k8s.io/kubernetes/pkg/kubeapiserver/admission"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "NamespaceExists"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("NamespaceExists", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewExists(), nil
 	})
 }

plugin/pkg/admission/persistentvolume/label/admission.go

@@ -33,9 +33,11 @@ import (
 	vol "k8s.io/kubernetes/pkg/volume"
 )
 
+const PluginName = "PersistentVolumeLabel"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("PersistentVolumeLabel", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		persistentVolumeLabelAdmission := NewPersistentVolumeLabel()
 		return persistentVolumeLabelAdmission, nil
 	})

plugin/pkg/admission/podnodeselector/admission.go

@@ -40,9 +40,11 @@ import (
 // node selectors labels to namespaces
 var NamespaceNodeSelectors = []string{"scheduler.alpha.kubernetes.io/node-selector"}
 
+const PluginName = "PodNodeSelector"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("PodNodeSelector", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		// TODO move this to a versioned configuration file format.
 		pluginConfig := readConfig(config)
 		plugin := NewPodNodeSelector(pluginConfig.PodNodeSelectorPluginConfig)

plugin/pkg/admission/podpreset/admission.go

@@ -41,12 +41,12 @@ import (
 
 const (
 	annotationPrefix = "podpreset.admission.kubernetes.io"
-	pluginName       = "PodPreset"
+	PluginName       = "PodPreset"
 )
 
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register(pluginName, func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewPlugin(), nil
 	})
 }
@@ -72,10 +72,10 @@ func NewPlugin() *podPresetPlugin {
 
 func (plugin *podPresetPlugin) ValidateInitialization() error {
 	if plugin.client == nil {
-		return fmt.Errorf("%s requires a client", pluginName)
+		return fmt.Errorf("%s requires a client", PluginName)
 	}
 	if plugin.lister == nil {
-		return fmt.Errorf("%s requires a lister", pluginName)
+		return fmt.Errorf("%s requires a lister", PluginName)
 	}
 	return nil
 }

plugin/pkg/admission/podtolerationrestriction/admission.go

@@ -40,9 +40,11 @@ import (
 	pluginapi "k8s.io/kubernetes/plugin/pkg/admission/podtolerationrestriction/apis/podtolerationrestriction"
 )
 
+const PluginName = "PodTolerationRestriction"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("PodTolerationRestriction", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		pluginConfig, err := loadConfiguration(config)
 		if err != nil {
 			return nil, err

plugin/pkg/admission/priority/admission.go

@@ -34,7 +34,8 @@ import (
 )
 
 const (
-	pluginName = "Priority"
+	// PluginName indicates name of admission plugin.
+	PluginName = "Priority"
 
 	// HighestUserDefinablePriority is the highest priority for user defined priority classes. Priority values larger than 1 billion are reserved for Kubernetes system use.
 	HighestUserDefinablePriority = 1000000000
@@ -50,7 +51,7 @@ var SystemPriorityClasses = map[string]int32{
 
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register(pluginName, func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewPlugin(), nil
 	})
 }
@@ -79,10 +80,10 @@ func NewPlugin() *PriorityPlugin {
 // ValidateInitialization implements the InitializationValidator interface.
 func (p *PriorityPlugin) ValidateInitialization() error {
 	if p.client == nil {
-		return fmt.Errorf("%s requires a client", pluginName)
+		return fmt.Errorf("%s requires a client", PluginName)
 	}
 	if p.lister == nil {
-		return fmt.Errorf("%s requires a lister", pluginName)
+		return fmt.Errorf("%s requires a lister", PluginName)
 	}
 	return nil
 }

plugin/pkg/admission/resourcequota/admission.go

@@ -31,9 +31,11 @@ import (
 	"k8s.io/kubernetes/plugin/pkg/admission/resourcequota/apis/resourcequota/validation"
 )
 
+const PluginName = "ResourceQuota"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("ResourceQuota",
+	plugins.Register(PluginName,
 		func(config io.Reader) (admission.Interface, error) {
 			// load the configuration provided (if any)
 			configuration, err := LoadConfiguration(config)

plugin/pkg/admission/securitycontext/scdeny/admission.go

@@ -25,9 +25,12 @@ import (
 	api "k8s.io/kubernetes/pkg/apis/core"
 )
 
+// PluginName indicates name of admission plugin.
+const PluginName = "SecurityContextDeny"
+
 // Register registers a plugin
 func Register(plugins *admission.Plugins) {
-	plugins.Register("SecurityContextDeny", func(config io.Reader) (admission.Interface, error) {
+	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
 		return NewSecurityContextDeny(), nil
 	})
 }

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/rest.go

@@ -110,7 +110,7 @@ func ConnectResource(connecter rest.Connecter, scope RequestScope, admit admissi
 			scope.err(err, w, req)
 			return
 		}
-		if admit.Handles(admission.Connect) {
+		if admit != nil && admit.Handles(admission.Connect) {
 			connectRequest := &rest.ConnectRequest{
 				Name:         name,
 				Options:      opts,

staging/src/k8s.io/apiserver/pkg/server/options/admission.go

@@ -21,6 +21,7 @@ import (
 	"strings"
 
 	"github.com/spf13/pflag"
+
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apiserver/pkg/admission"
@@ -49,11 +50,16 @@ func init() {
 type AdmissionOptions struct {
 	// RecommendedPluginOrder holds an ordered list of plugin names we recommend to use by default
 	RecommendedPluginOrder []string
-	// DefaultOffPlugins a list of plugin names that should be disabled by default
-	DefaultOffPlugins []string
-	PluginNames       []string
-	ConfigFile        string
-
+	// DefaultOffPlugins is a set of plugin names that is disabled by default
+	DefaultOffPlugins sets.String
+
+	// EnablePlugins indicates plugins to be enabled passed through `--enable-admission-plugins`.
+	EnablePlugins []string
+	// DisablePlugins indicates plugins to be disabled passed through `--disable-admission-plugins`.
+	DisablePlugins []string
+	// ConfigFile is the file path with admission control configuration.
+	ConfigFile string
+	// Plugins contains all registered plugins.
 	Plugins *admission.Plugins
 }
 
@@ -67,14 +73,13 @@ type AdmissionOptions struct {
 //  Servers that do care can overwrite/append that field after creation.
 func NewAdmissionOptions() *AdmissionOptions {
 	options := &AdmissionOptions{
-		Plugins:     admission.NewPlugins(),
-		PluginNames: []string{},
+		Plugins: admission.NewPlugins(),
 		// This list is mix of mutating admission plugins and validating
 		// admission plugins. The apiserver always runs the validating ones
 		// after all the mutating ones, so their relative order in this list
 		// doesn't matter.
 		RecommendedPluginOrder: []string{lifecycle.PluginName, initialization.PluginName, mutatingwebhook.PluginName, validatingwebhook.PluginName},
-		DefaultOffPlugins:      []string{initialization.PluginName, mutatingwebhook.PluginName, validatingwebhook.PluginName},
+		DefaultOffPlugins:      sets.NewString(initialization.PluginName, mutatingwebhook.PluginName, validatingwebhook.PluginName),
 	}
 	server.RegisterAllAdmissionPlugins(options.Plugins)
 	return options
@@ -82,14 +87,14 @@ func NewAdmissionOptions() *AdmissionOptions {
 
 // AddFlags adds flags related to admission for a specific APIServer to the specified FlagSet
 func (a *AdmissionOptions) AddFlags(fs *pflag.FlagSet) {
-	fs.StringSliceVar(&a.PluginNames, "admission-control", a.PluginNames, ""+
-		"Admission is divided into two phases. "+
-		"In the first phase, only mutating admission plugins run. "+
-		"In the second phase, only validating admission plugins run. "+
-		"The names in the below list may represent a validating plugin, a mutating plugin, or both. "+
-		"Within each phase, the plugins will run in the order in which they are passed to this flag. "+
-		"Comma-delimited list of: "+strings.Join(a.Plugins.Registered(), ", ")+".")
-
+	fs.StringSliceVar(&a.EnablePlugins, "enable-admission-plugins", a.EnablePlugins, ""+
+		"admission plugins that should be enabled in addition to default enabled ones. "+
+		"Comma-delimited list of admission plugins: "+strings.Join(a.Plugins.Registered(), ", ")+". "+
+		"The order of plugins in this flag does not matter.")
+	fs.StringSliceVar(&a.DisablePlugins, "disable-admission-plugins", a.DisablePlugins, ""+
+		"admission plugins that should be disabled although they are in the default enabled plugins list. "+
+		"Comma-delimited list of admission plugins: "+strings.Join(a.Plugins.Registered(), ", ")+". "+
+		"The order of plugins in this flag does not matter.")
 	fs.StringVar(&a.ConfigFile, "admission-control-config-file", a.ConfigFile,
 		"File with admission control configuration.")
 }
@@ -120,10 +125,7 @@ func (a *AdmissionOptions) ApplyTo(
 		return fmt.Errorf("admission depends on a Kubernetes core API shared informer, it cannot be nil")
 	}
 
-	pluginNames := a.PluginNames
-	if len(a.PluginNames) == 0 {
-		pluginNames = a.enabledPluginNames()
-	}
+	pluginNames := a.enabledPluginNames()
 
 	pluginsConfigProvider, err := admission.ReadAdmissionConfiguration(pluginNames, a.ConfigFile, configScheme)
 	if err != nil {
@@ -148,6 +150,7 @@ func (a *AdmissionOptions) ApplyTo(
 	return nil
 }
 
+// Validate verifies flags passed to AdmissionOptions.
 func (a *AdmissionOptions) Validate() []error {
 	if a == nil {
 		return nil
@@ -156,41 +159,57 @@ func (a *AdmissionOptions) Validate() []error {
 	errs := []error{}
 
 	registeredPlugins := sets.NewString(a.Plugins.Registered()...)
-	for _, name := range a.PluginNames {
+	for _, name := range a.EnablePlugins {
+		if !registeredPlugins.Has(name) {
+			errs = append(errs, fmt.Errorf("enable-admission-plugins plugin %q is unknown", name))
+		}
+	}
+
+	for _, name := range a.DisablePlugins {
 		if !registeredPlugins.Has(name) {
-			errs = append(errs, fmt.Errorf("admission-control plugin %q is invalid", name))
+			errs = append(errs, fmt.Errorf("disable-admission-plugins plugin %q is unknown", name))
 		}
 	}
 
+	enablePlugins := sets.NewString(a.EnablePlugins...)
+	disablePlugins := sets.NewString(a.DisablePlugins...)
+	if len(enablePlugins.Intersection(disablePlugins).List()) > 0 {
+		errs = append(errs, fmt.Errorf("%v in enable-admission-plugins and disable-admission-plugins "+
+			"overlapped", enablePlugins.Intersection(disablePlugins).List()))
+	}
+
+	// Verify RecommendedPluginOrder.
+	recommendPlugins := sets.NewString(a.RecommendedPluginOrder...)
+	intersections := registeredPlugins.Intersection(recommendPlugins)
+	if !intersections.Equal(recommendPlugins) {
+		// Developer error, this should never run in.
+		errs = append(errs, fmt.Errorf("plugins %v in RecommendedPluginOrder are not registered",
+			recommendPlugins.Difference(intersections).List()))
+	}
+	if !intersections.Equal(registeredPlugins) {
+		// Developer error, this should never run in.
+		errs = append(errs, fmt.Errorf("plugins %v registered are not in RecommendedPluginOrder",
+			registeredPlugins.Difference(intersections).List()))
+	}
+
 	return errs
 }
 
-// enabledPluginNames makes use of RecommendedPluginOrder and DefaultOffPlugins fields
-// to prepare a list of plugin names that are enabled.
-//
-// TODO(p0lyn0mial): In the end we will introduce two new flags:
-// --disable-admission-plugin this would be a list of admission plugins that a cluster-admin wants to explicitly disable.
-// --enable-admission-plugin  this would be a list of admission plugins that a cluster-admin wants to explicitly enable.
-// both flags are going to be handled by this method
+// enabledPluginNames makes use of RecommendedPluginOrder, DefaultOffPlugins,
+// EnablePlugins, DisablePlugins fields
+// to prepare a list of ordered plugin names that are enabled.
 func (a *AdmissionOptions) enabledPluginNames() []string {
-	//TODO(p0lyn0mial): first subtract plugins that a user wants to explicitly enable from allOffPlugins (DefaultOffPlugins)
-	//TODO(p0lyn0miial): then add/append plugins that a user wants to explicitly disable to allOffPlugins
-	//TODO(p0lyn0mial): so that --off=three --on=one,three default-off=one,two results in  "one" being enabled.
-	allOffPlugins := a.DefaultOffPlugins
-	onlyEnabledPluginNames := []string{}
-	for _, pluginName := range a.RecommendedPluginOrder {
-		disablePlugin := false
-		for _, disabledPluginName := range allOffPlugins {
-			if pluginName == disabledPluginName {
-				disablePlugin = true
-				break
-			}
-		}
-		if disablePlugin {
-			continue
+	allOffPlugins := append(a.DefaultOffPlugins.List(), a.DisablePlugins...)
+	disabledPlugins := sets.NewString(allOffPlugins...)
+	enabledPlugins := sets.NewString(a.EnablePlugins...)
+	disabledPlugins = disabledPlugins.Difference(enabledPlugins)
+
+	orderedPlugins := []string{}
+	for _, plugin := range a.RecommendedPluginOrder {
+		if !disabledPlugins.Has(plugin) {
+			orderedPlugins = append(orderedPlugins, plugin)
 		}
-		onlyEnabledPluginNames = append(onlyEnabledPluginNames, pluginName)
 	}
 
-	return onlyEnabledPluginNames
+	return orderedPlugins
 }