Merge pull request #66936 from jennybuckley/dry-run-webhooks

api/openapi-spec/swagger.json

@@ -73548,6 +73548,10 @@
       "items": {
        "$ref": "#/definitions/io.k8s.api.admissionregistration.v1beta1.RuleWithOperations"
       }
+     },
+     "sideEffects": {
+      "description": "SideEffects states whether this webhookk has side effects. Acceptable values are: Unknown, None, Some, NoneOnDryRun Webhooks with side effects MUST implement a reconciliation system, since a request may be rejected by a future step in the admission change and the side effects therefore need to be undone. Requests with the dryRun attribute will be auto-rejected if they match a webhook with sideEffects == Unknown or Some. Defaults to Unknown.",
+      "type": "string"
      }
     }
    },

api/swagger-spec/admissionregistration.k8s.io_v1beta1.json

@@ -1786,6 +1786,10 @@
      "namespaceSelector": {
       "$ref": "v1.LabelSelector",
       "description": "NamespaceSelector decides whether to run the webhook on an object based on whether the namespace for that object matches the selector. If the object itself is a namespace, the matching is performed on object.metadata.labels. If the object is another cluster scoped resource, it never skips the webhook.\n\nFor example, to run the webhook on any objects whose namespace is not associated with \"runlevel\" of \"0\" or \"1\";  you will set the selector as follows: \"namespaceSelector\": {\n  \"matchExpressions\": [\n    {\n      \"key\": \"runlevel\",\n      \"operator\": \"NotIn\",\n      \"values\": [\n        \"0\",\n        \"1\"\n      ]\n    }\n  ]\n}\n\nIf instead you want to only run the webhook on any objects whose namespace is associated with the \"environment\" of \"prod\" or \"staging\"; you will set the selector as follows: \"namespaceSelector\": {\n  \"matchExpressions\": [\n    {\n      \"key\": \"environment\",\n      \"operator\": \"In\",\n      \"values\": [\n        \"prod\",\n        \"staging\"\n      ]\n    }\n  ]\n}\n\nSee https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/ for more examples of label selectors.\n\nDefault to the empty LabelSelector, which matches everything."
+     },
+     "sideEffects": {
+      "$ref": "v1beta1.SideEffectClass",
+      "description": "SideEffects states whether this webhookk has side effects. Acceptable values are: Unknown, None, Some, NoneOnDryRun Webhooks with side effects MUST implement a reconciliation system, since a request may be rejected by a future step in the admission change and the side effects therefore need to be undone. Requests with the dryRun attribute will be auto-rejected if they match a webhook with sideEffects == Unknown or Some. Defaults to Unknown."
      }
     }
    },
@@ -1917,6 +1921,10 @@
      }
     }
    },
+   "v1beta1.SideEffectClass": {
+    "id": "v1beta1.SideEffectClass",
+    "properties": {}
+   },
    "v1.WatchEvent": {
     "id": "v1.WatchEvent",
     "required": [

docs/api-reference/admissionregistration.k8s.io/v1beta1/definitions.html

@@ -1051,6 +1051,10 @@ Depending on the enclosing object, subresources might not be allowed. Required.<
 
 </div>
 <div class="sect2">
+<h3 id="_v1_deletionpropagation">v1.DeletionPropagation</h3>
+
+</div>
+<div class="sect2">
 <h3 id="_v1beta1_webhook">v1beta1.Webhook</h3>
 <div class="paragraph">
 <p>Webhook describes an admission webhook and the resources and operations it applies to.</p>
@@ -1138,15 +1142,18 @@ Default to the empty LabelSelector, which matches everything.</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_v1_labelselector">v1.LabelSelector</a></p></td>
 <td class="tableblock halign-left valign-top"></td>
 </tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p class="tableblock">sideEffects</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">SideEffects states whether this webhookk has side effects. Acceptable values are: Unknown, None, Some, NoneOnDryRun Webhooks with side effects MUST implement a reconciliation system, since a request may be rejected by a future step in the admission change and the side effects therefore need to be undone. Requests with the dryRun attribute will be auto-rejected if they match a webhook with sideEffects == Unknown or Some. Defaults to Unknown.</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">false</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_v1beta1_sideeffectclass">v1beta1.SideEffectClass</a></p></td>
+<td class="tableblock halign-left valign-top"></td>
+</tr>
 </tbody>
 </table>
 
 </div>
 <div class="sect2">
-<h3 id="_v1_deletionpropagation">v1.DeletionPropagation</h3>
-
-</div>
-<div class="sect2">
 <h3 id="_v1beta1_operationtype">v1beta1.OperationType</h3>
 
 </div>
@@ -1767,6 +1774,10 @@ Port 443 will be used if it is open, otherwise it is an error.</p></td>
 
 </div>
 <div class="sect2">
+<h3 id="_v1beta1_sideeffectclass">v1beta1.SideEffectClass</h3>
+
+</div>
+<div class="sect2">
 <h3 id="_types_uid">types.UID</h3>
 
 </div>

pkg/apis/admission/types.go

@@ -73,6 +73,11 @@ type AdmissionRequest struct {
 	// OldObject is the existing object. Only populated for UPDATE requests.
 	// +optional
 	OldObject runtime.Object
+	// DryRun indicates that modifications will definitely not be persisted for this request.
+	// Calls to webhooks must have no side effects if DryRun is true.
+	// Defaults to false.
+	// +optional
+	DryRun *bool
 }
 
 // AdmissionResponse describes an admission response.

pkg/apis/admission/v1beta1/zz_generated.conversion.go

@@ -89,6 +89,7 @@ func autoConvert_v1beta1_AdmissionRequest_To_admission_AdmissionRequest(in *v1be
 	if err := runtime.Convert_runtime_RawExtension_To_runtime_Object(&in.OldObject, &out.OldObject, s); err != nil {
 		return err
 	}
+	out.DryRun = (*bool)(unsafe.Pointer(in.DryRun))
 	return nil
 }
 
@@ -115,6 +116,7 @@ func autoConvert_admission_AdmissionRequest_To_v1beta1_AdmissionRequest(in *admi
 	if err := runtime.Convert_runtime_Object_To_runtime_RawExtension(&in.OldObject, &out.OldObject, s); err != nil {
 		return err
 	}
+	out.DryRun = (*bool)(unsafe.Pointer(in.DryRun))
 	return nil
 }
 

pkg/apis/admission/zz_generated.deepcopy.go

@@ -37,6 +37,11 @@ func (in *AdmissionRequest) DeepCopyInto(out *AdmissionRequest) {
 	if in.OldObject != nil {
 		out.OldObject = in.OldObject.DeepCopyObject()
 	}
+	if in.DryRun != nil {
+		in, out := &in.DryRun, &out.DryRun
+		*out = new(bool)
+		**out = **in
+	}
 	return
 }
 

pkg/apis/admissionregistration/fuzzer/fuzzer.go

@@ -30,6 +30,8 @@ var Funcs = func(codecs runtimeserializer.CodecFactory) []interface{} {
 			c.FuzzNoCustom(obj) // fuzz self without calling this function again
 			p := admissionregistration.FailurePolicyType("Fail")
 			obj.FailurePolicy = &p
+			s := admissionregistration.SideEffectClassUnknown
+			obj.SideEffects = &s
 		},
 	}
 }

pkg/apis/admissionregistration/types.go

@@ -112,6 +112,22 @@ const (
 	Fail FailurePolicyType = "Fail"
 )
 
+type SideEffectClass string
+
+const (
+	// SideEffectClassUnknown means that no information is known about the side effects of calling the webhook.
+	// If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail.
+	SideEffectClassUnknown SideEffectClass = "Unknown"
+	// SideEffectClassNone means that calling the webhook will have no side effects.
+	SideEffectClassNone SideEffectClass = "None"
+	// SideEffectClassSome means that calling the webhook will possibly have side effects.
+	// If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail.
+	SideEffectClassSome SideEffectClass = "Some"
+	// SideEffectClassNoneOnDryRun means that calling the webhook will possibly have side effects, but if the
+	// request being reviewed has the dry-run attribute, the side effects will be suppressed.
+	SideEffectClassNoneOnDryRun SideEffectClass = "NoneOnDryRun"
+)
+
 // +genclient
 // +genclient:nonNamespaced
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
@@ -235,6 +251,15 @@ type Webhook struct {
 	// Default to the empty LabelSelector, which matches everything.
 	// +optional
 	NamespaceSelector *metav1.LabelSelector
+
+	// SideEffects states whether this webhookk has side effects.
+	// Acceptable values are: Unknown, None, Some, NoneOnDryRun
+	// Webhooks with side effects MUST implement a reconciliation system, since a request may be
+	// rejected by a future step in the admission change and the side effects therefore need to be undone.
+	// Requests with the dryRun attribute will be auto-rejected if they match a webhook with
+	// sideEffects == Unknown or Some. Defaults to Unknown.
+	// +optional
+	SideEffects *SideEffectClass
 }
 
 // RuleWithOperations is a tuple of Operations and Resources. It is recommended to make

pkg/apis/admissionregistration/v1beta1/defaults.go

@@ -35,4 +35,9 @@ func SetDefaults_Webhook(obj *admissionregistrationv1beta1.Webhook) {
 		selector := metav1.LabelSelector{}
 		obj.NamespaceSelector = &selector
 	}
+	if obj.SideEffects == nil {
+		// TODO: revisit/remove this default and possibly make the field required when promoting to v1
+		unknown := admissionregistrationv1beta1.SideEffectClassUnknown
+		obj.SideEffects = &unknown
+	}
 }

pkg/apis/admissionregistration/v1beta1/zz_generated.conversion.go

@@ -300,6 +300,7 @@ func autoConvert_v1beta1_Webhook_To_admissionregistration_Webhook(in *v1beta1.We
 	out.Rules = *(*[]admissionregistration.RuleWithOperations)(unsafe.Pointer(&in.Rules))
 	out.FailurePolicy = (*admissionregistration.FailurePolicyType)(unsafe.Pointer(in.FailurePolicy))
 	out.NamespaceSelector = (*v1.LabelSelector)(unsafe.Pointer(in.NamespaceSelector))
+	out.SideEffects = (*admissionregistration.SideEffectClass)(unsafe.Pointer(in.SideEffects))
 	return nil
 }
 
@@ -316,6 +317,7 @@ func autoConvert_admissionregistration_Webhook_To_v1beta1_Webhook(in *admissionr
 	out.Rules = *(*[]v1beta1.RuleWithOperations)(unsafe.Pointer(&in.Rules))
 	out.FailurePolicy = (*v1beta1.FailurePolicyType)(unsafe.Pointer(in.FailurePolicy))
 	out.NamespaceSelector = (*v1.LabelSelector)(unsafe.Pointer(in.NamespaceSelector))
+	out.SideEffects = (*v1beta1.SideEffectClass)(unsafe.Pointer(in.SideEffects))
 	return nil
 }
 

pkg/apis/admissionregistration/validation/validation.go

@@ -192,6 +192,9 @@ func validateWebhook(hook *admissionregistration.Webhook, fldPath *field.Path) f
 	if hook.FailurePolicy != nil && !supportedFailurePolicies.Has(string(*hook.FailurePolicy)) {
 		allErrors = append(allErrors, field.NotSupported(fldPath.Child("failurePolicy"), *hook.FailurePolicy, supportedFailurePolicies.List()))
 	}
+	if hook.SideEffects != nil && !supportedSideEffectClasses.Has(string(*hook.SideEffects)) {
+		allErrors = append(allErrors, field.NotSupported(fldPath.Child("sideEffects"), *hook.SideEffects, supportedSideEffectClasses.List()))
+	}
 
 	if hook.NamespaceSelector != nil {
 		allErrors = append(allErrors, metav1validation.ValidateLabelSelector(hook.NamespaceSelector, fldPath.Child("namespaceSelector"))...)
@@ -291,6 +294,13 @@ var supportedFailurePolicies = sets.NewString(
 	string(admissionregistration.Fail),
 )
 
+var supportedSideEffectClasses = sets.NewString(
+	string(admissionregistration.SideEffectClassUnknown),
+	string(admissionregistration.SideEffectClassNone),
+	string(admissionregistration.SideEffectClassSome),
+	string(admissionregistration.SideEffectClassNoneOnDryRun),
+)
+
 var supportedOperations = sets.NewString(
 	string(admissionregistration.OperationAll),
 	string(admissionregistration.Create),

pkg/apis/admissionregistration/validation/validation_test.go

@@ -500,6 +500,21 @@ func TestValidateValidatingWebhookConfiguration(t *testing.T) {
 			expectedError: `webhooks[0].failurePolicy: Unsupported value: "other": supported values: "Fail", "Ignore"`,
 		},
 		{
+			name: "SideEffects can only be \"Unknown\", \"None\", \"Some\", or \"NoneOnDryRun\"",
+			config: newValidatingWebhookConfiguration(
+				[]admissionregistration.Webhook{
+					{
+						Name:         "webhook.k8s.io",
+						ClientConfig: validClientConfig,
+						SideEffects: func() *admissionregistration.SideEffectClass {
+							r := admissionregistration.SideEffectClass("other")
+							return &r
+						}(),
+					},
+				}),
+			expectedError: `webhooks[0].sideEffects: Unsupported value: "other": supported values: "None", "NoneOnDryRun", "Some", "Unknown"`,
+		},
+		{
 			name: "both service and URL missing",
 			config: newValidatingWebhookConfiguration(
 				[]admissionregistration.Webhook{

pkg/apis/admissionregistration/zz_generated.deepcopy.go

@@ -341,6 +341,11 @@ func (in *Webhook) DeepCopyInto(out *Webhook) {
 		*out = new(v1.LabelSelector)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.SideEffects != nil {
+		in, out := &in.SideEffects, &out.SideEffects
+		*out = new(SideEffectClass)
+		**out = **in
+	}
 	return
 }
 

staging/src/k8s.io/api/admission/v1beta1/generated.proto

@@ -73,6 +73,11 @@ message AdmissionRequest {
   // OldObject is the existing object. Only populated for UPDATE requests.
   // +optional
   optional k8s.io.apimachinery.pkg.runtime.RawExtension oldObject = 10;
+
+  // DryRun indicates that modifications will definitely not be persisted for this request.
+  // Defaults to false.
+  // +optional
+  optional bool dryRun = 11;
 }
 
 // AdmissionResponse describes an admission response.

staging/src/k8s.io/api/admission/v1beta1/types.go

@@ -71,6 +71,10 @@ type AdmissionRequest struct {
 	// OldObject is the existing object. Only populated for UPDATE requests.
 	// +optional
 	OldObject runtime.RawExtension `json:"oldObject,omitempty" protobuf:"bytes,10,opt,name=oldObject"`
+	// DryRun indicates that modifications will definitely not be persisted for this request.
+	// Defaults to false.
+	// +optional
+	DryRun *bool `json:"dryRun,omitempty" protobuf:"varint,11,opt,name=dryRun"`
 }
 
 // AdmissionResponse describes an admission response.

staging/src/k8s.io/api/admission/v1beta1/types_swagger_doc_generated.go

@@ -39,6 +39,7 @@ var map_AdmissionRequest = map[string]string{
 	"userInfo":    "UserInfo is information about the requesting user",
 	"object":      "Object is the object from the incoming request prior to default values being applied",
 	"oldObject":   "OldObject is the existing object. Only populated for UPDATE requests.",
+	"dryRun":      "DryRun indicates that modifications will definitely not be persisted for this request. Defaults to false.",
 }
 
 func (AdmissionRequest) SwaggerDoc() map[string]string {

staging/src/k8s.io/api/admission/v1beta1/zz_generated.deepcopy.go

@@ -33,6 +33,11 @@ func (in *AdmissionRequest) DeepCopyInto(out *AdmissionRequest) {
 	in.UserInfo.DeepCopyInto(&out.UserInfo)
 	in.Object.DeepCopyInto(&out.Object)
 	in.OldObject.DeepCopyInto(&out.OldObject)
+	if in.DryRun != nil {
+		in, out := &in.DryRun, &out.DryRun
+		*out = new(bool)
+		**out = **in
+	}
 	return
 }
 

staging/src/k8s.io/api/admissionregistration/v1beta1/generated.proto

@@ -208,6 +208,15 @@ message Webhook {
   // Default to the empty LabelSelector, which matches everything.
   // +optional
   optional k8s.io.apimachinery.pkg.apis.meta.v1.LabelSelector namespaceSelector = 5;
+
+  // SideEffects states whether this webhookk has side effects.
+  // Acceptable values are: Unknown, None, Some, NoneOnDryRun
+  // Webhooks with side effects MUST implement a reconciliation system, since a request may be
+  // rejected by a future step in the admission change and the side effects therefore need to be undone.
+  // Requests with the dryRun attribute will be auto-rejected if they match a webhook with
+  // sideEffects == Unknown or Some. Defaults to Unknown.
+  // +optional
+  optional string sideEffects = 6;
 }
 
 // WebhookClientConfig contains the information to make a TLS

staging/src/k8s.io/api/admissionregistration/v1beta1/types.go

@@ -60,6 +60,22 @@ const (
 	Fail FailurePolicyType = "Fail"
 )
 
+type SideEffectClass string
+
+const (
+	// SideEffectClassUnknown means that no information is known about the side effects of calling the webhook.
+	// If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail.
+	SideEffectClassUnknown SideEffectClass = "Unknown"
+	// SideEffectClassNone means that calling the webhook will have no side effects.
+	SideEffectClassNone SideEffectClass = "None"
+	// SideEffectClassSome means that calling the webhook will possibly have side effects.
+	// If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail.
+	SideEffectClassSome SideEffectClass = "Some"
+	// SideEffectClassNoneOnDryRun means that calling the webhook will possibly have side effects, but if the
+	// request being reviewed has the dry-run attribute, the side effects will be suppressed.
+	SideEffectClassNoneOnDryRun SideEffectClass = "NoneOnDryRun"
+)
+
 // +genclient
 // +genclient:nonNamespaced
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
@@ -191,6 +207,15 @@ type Webhook struct {
 	// Default to the empty LabelSelector, which matches everything.
 	// +optional
 	NamespaceSelector *metav1.LabelSelector `json:"namespaceSelector,omitempty" protobuf:"bytes,5,opt,name=namespaceSelector"`
+
+	// SideEffects states whether this webhookk has side effects.
+	// Acceptable values are: Unknown, None, Some, NoneOnDryRun
+	// Webhooks with side effects MUST implement a reconciliation system, since a request may be
+	// rejected by a future step in the admission change and the side effects therefore need to be undone.
+	// Requests with the dryRun attribute will be auto-rejected if they match a webhook with
+	// sideEffects == Unknown or Some. Defaults to Unknown.
+	// +optional
+	SideEffects *SideEffectClass `json:"sideEffects,omitempty" protobuf:"bytes,6,opt,name=sideEffects,casttype=SideEffectClass"`
 }
 
 // RuleWithOperations is a tuple of Operations and Resources. It is recommended to make

staging/src/k8s.io/api/admissionregistration/v1beta1/types_swagger_doc_generated.go

@@ -105,6 +105,7 @@ var map_Webhook = map[string]string{
 	"rules":             "Rules describes what operations on what resources/subresources the webhook cares about. The webhook cares about an operation if it matches _any_ Rule. However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks from putting the cluster in a state which cannot be recovered from without completely disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called on admission requests for ValidatingWebhookConfiguration and MutatingWebhookConfiguration objects.",
 	"failurePolicy":     "FailurePolicy defines how unrecognized errors from the admission endpoint are handled - allowed values are Ignore or Fail. Defaults to Ignore.",
 	"namespaceSelector": "NamespaceSelector decides whether to run the webhook on an object based on whether the namespace for that object matches the selector. If the object itself is a namespace, the matching is performed on object.metadata.labels. If the object is another cluster scoped resource, it never skips the webhook.\n\nFor example, to run the webhook on any objects whose namespace is not associated with \"runlevel\" of \"0\" or \"1\";  you will set the selector as follows: \"namespaceSelector\": {\n  \"matchExpressions\": [\n    {\n      \"key\": \"runlevel\",\n      \"operator\": \"NotIn\",\n      \"values\": [\n        \"0\",\n        \"1\"\n      ]\n    }\n  ]\n}\n\nIf instead you want to only run the webhook on any objects whose namespace is associated with the \"environment\" of \"prod\" or \"staging\"; you will set the selector as follows: \"namespaceSelector\": {\n  \"matchExpressions\": [\n    {\n      \"key\": \"environment\",\n      \"operator\": \"In\",\n      \"values\": [\n        \"prod\",\n        \"staging\"\n      ]\n    }\n  ]\n}\n\nSee https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/ for more examples of label selectors.\n\nDefault to the empty LabelSelector, which matches everything.",
+	"sideEffects":       "SideEffects states whether this webhookk has side effects. Acceptable values are: Unknown, None, Some, NoneOnDryRun Webhooks with side effects MUST implement a reconciliation system, since a request may be rejected by a future step in the admission change and the side effects therefore need to be undone. Requests with the dryRun attribute will be auto-rejected if they match a webhook with sideEffects == Unknown or Some. Defaults to Unknown.",
 }
 
 func (Webhook) SwaggerDoc() map[string]string {

staging/src/k8s.io/api/admissionregistration/v1beta1/zz_generated.deepcopy.go

@@ -252,6 +252,11 @@ func (in *Webhook) DeepCopyInto(out *Webhook) {
 		*out = new(v1.LabelSelector)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.SideEffects != nil {
+		in, out := &in.SideEffects, &out.SideEffects
+		*out = new(SideEffectClass)
+		**out = **in
+	}
 	return
 }
 

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/mutating/dispatcher.go

@@ -83,8 +83,12 @@ func (a *mutatingDispatcher) Dispatch(ctx context.Context, attr *generic.Version
 // note that callAttrMutatingHook updates attr
 func (a *mutatingDispatcher) callAttrMutatingHook(ctx context.Context, h *v1beta1.Webhook, attr *generic.VersionedAttributes) error {
 	if attr.IsDryRun() {
-		// TODO: support this
-		return webhookerrors.NewDryRunUnsupportedErr(h.Name)
+		if h.SideEffects == nil {
+			return &webhookerrors.ErrCallingWebhook{WebhookName: h.Name, Reason: fmt.Errorf("Webhook SideEffects is nil")}
+		}
+		if !(*h.SideEffects == v1beta1.SideEffectClassNone || *h.SideEffects == v1beta1.SideEffectClassNoneOnDryRun) {
+			return webhookerrors.NewDryRunUnsupportedErr(h.Name)
+		}
 	}
 
 	// Make the webhook request

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/request/admissionreview.go

@@ -36,6 +36,7 @@ func CreateAdmissionReview(attr *generic.VersionedAttributes) admissionv1beta1.A
 		UID:      aUserInfo.GetUID(),
 		Username: aUserInfo.GetName(),
 	}
+	dryRun := attr.IsDryRun()
 
 	// Convert the extra information in the user object
 	for key, val := range aUserInfo.GetExtra() {
@@ -66,6 +67,7 @@ func CreateAdmissionReview(attr *generic.VersionedAttributes) admissionv1beta1.A
 			OldObject: runtime.RawExtension{
 				Object: attr.VersionedOldObject,
 			},
+			DryRun: &dryRun,
 		},
 	}
 }

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/testing/testcase.go

@@ -43,6 +43,11 @@ var matchEverythingRules = []registrationv1beta1.RuleWithOperations{{
 	},
 }}
 
+var sideEffectsUnknown registrationv1beta1.SideEffectClass = registrationv1beta1.SideEffectClassUnknown
+var sideEffectsNone registrationv1beta1.SideEffectClass = registrationv1beta1.SideEffectClassNone
+var sideEffectsSome registrationv1beta1.SideEffectClass = registrationv1beta1.SideEffectClassSome
+var sideEffectsNoneOnDryRun registrationv1beta1.SideEffectClass = registrationv1beta1.SideEffectClassNoneOnDryRun
+
 // NewFakeDataSource returns a mock client and informer returning the given webhooks.
 func NewFakeDataSource(name string, webhooks []registrationv1beta1.Webhook, mutating bool, stopCh <-chan struct{}) (clientset kubernetes.Interface, factory informers.SharedInformerFactory) {
 	var objs = []runtime.Object{
@@ -388,27 +393,67 @@ func NewNonMutatingTestCases(url *url.URL) []Test {
 			Name: "no match dry run",
 			Webhooks: []registrationv1beta1.Webhook{{
 				Name:         "nomatch",
-				ClientConfig: ccfgSVC("disallow"),
+				ClientConfig: ccfgSVC("allow"),
 				Rules: []registrationv1beta1.RuleWithOperations{{
 					Operations: []registrationv1beta1.OperationType{registrationv1beta1.Create},
 				}},
 				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsSome,
 			}},
 			IsDryRun:    true,
 			ExpectAllow: true,
 		},
 		{
-			Name: "match dry run",
+			Name: "match dry run side effects Unknown",
+			Webhooks: []registrationv1beta1.Webhook{{
+				Name:              "allow",
+				ClientConfig:      ccfgSVC("allow"),
+				Rules:             matchEverythingRules,
+				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsUnknown,
+			}},
+			IsDryRun:      true,
+			ErrorContains: "does not support dry run",
+		},
+		{
+			Name: "match dry run side effects None",
+			Webhooks: []registrationv1beta1.Webhook{{
+				Name:              "allow",
+				ClientConfig:      ccfgSVC("allow"),
+				Rules:             matchEverythingRules,
+				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsNone,
+			}},
+			IsDryRun:          true,
+			ExpectAllow:       true,
+			ExpectAnnotations: map[string]string{"allow/key1": "value1"},
+		},
+		{
+			Name: "match dry run side effects Some",
 			Webhooks: []registrationv1beta1.Webhook{{
 				Name:              "allow",
 				ClientConfig:      ccfgSVC("allow"),
 				Rules:             matchEverythingRules,
 				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsSome,
 			}},
 			IsDryRun:      true,
 			ErrorContains: "does not support dry run",
 		},
 		{
+			Name: "match dry run side effects NoneOnDryRun",
+			Webhooks: []registrationv1beta1.Webhook{{
+				Name:              "allow",
+				ClientConfig:      ccfgSVC("allow"),
+				Rules:             matchEverythingRules,
+				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsNoneOnDryRun,
+			}},
+			IsDryRun:          true,
+			ExpectAllow:       true,
+			ExpectAnnotations: map[string]string{"allow/key1": "value1"},
+		},
+		{
 			Name: "illegal annotation format",
 			Webhooks: []registrationv1beta1.Webhook{{
 				Name:              "invalidAnnotation",
@@ -489,12 +534,13 @@ func NewMutatingTestCases(url *url.URL) []Test {
 			ErrorContains: "invalid character",
 		},
 		{
-			Name: "match & remove label dry run",
+			Name: "match & remove label dry run unsupported",
 			Webhooks: []registrationv1beta1.Webhook{{
 				Name:              "removeLabel",
 				ClientConfig:      ccfgSVC("removeLabel"),
 				Rules:             matchEverythingRules,
 				NamespaceSelector: &metav1.LabelSelector{},
+				SideEffects:       &sideEffectsUnknown,
 			}},
 			IsDryRun:      true,
 			ErrorContains: "does not support dry run",

staging/src/k8s.io/apiserver/pkg/admission/plugin/webhook/validating/dispatcher.go

@@ -98,8 +98,12 @@ func (d *validatingDispatcher) Dispatch(ctx context.Context, attr *generic.Versi
 
 func (d *validatingDispatcher) callHook(ctx context.Context, h *v1beta1.Webhook, attr *generic.VersionedAttributes) error {
 	if attr.IsDryRun() {
-		// TODO: support this
-		return webhookerrors.NewDryRunUnsupportedErr(h.Name)
+		if h.SideEffects == nil {
+			return &webhookerrors.ErrCallingWebhook{WebhookName: h.Name, Reason: fmt.Errorf("Webhook SideEffects is nil")}
+		}
+		if !(*h.SideEffects == v1beta1.SideEffectClassNone || *h.SideEffects == v1beta1.SideEffectClassNoneOnDryRun) {
+			return webhookerrors.NewDryRunUnsupportedErr(h.Name)
+		}
 	}
 
 	// Make the webhook request