Merge pull request #67795 from mbohlool/crd_conversion_api_changes

api/openapi-spec/swagger.json

@@ -77309,7 +77309,7 @@
       "$ref": "#/definitions/io.k8s.api.admissionregistration.v1beta1.ServiceReference"
      },
      "url": {
-      "description": "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
+      "description": "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
       "type": "string"
      }
     }
@@ -79916,7 +79916,7 @@
       "$ref": "#/definitions/io.k8s.api.auditregistration.v1alpha1.ServiceReference"
      },
      "url": {
-      "description": "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
+      "description": "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
       "type": "string"
      }
     }
@@ -91823,6 +91823,22 @@
      }
     }
    },
+   "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceConversion": {
+    "description": "CustomResourceConversion describes how to convert different versions of a CR.",
+    "required": [
+     "strategy"
+    ],
+    "properties": {
+     "strategy": {
+      "description": "`strategy` specifies the conversion strategy. Allowed values are: - `None`: The converter only change the apiVersion and would not touch any other field in the CR. - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.",
+      "type": "string"
+     },
+     "webhookClientConfig": {
+      "description": "`webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`. This field is alpha-level and is only honored by servers that enable the CustomResourceWebhookConversion feature.",
+      "$ref": "#/definitions/io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.WebhookClientConfig"
+     }
+    }
+   },
    "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceDefinition": {
     "description": "CustomResourceDefinition represents a resource that should be exposed on the API server.  Its name MUST be in the format \u003c.spec.name\u003e.\u003c.spec.group\u003e.",
     "required": [
@@ -91973,6 +91989,10 @@
        "$ref": "#/definitions/io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceColumnDefinition"
       }
      },
+     "conversion": {
+      "description": "`conversion` defines conversion settings for the CRD.",
+      "$ref": "#/definitions/io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceConversion"
+     },
      "group": {
       "description": "Group is the group this resource belongs in",
       "type": "string"
@@ -92035,6 +92055,7 @@
     }
    },
    "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceDefinitionVersion": {
+    "description": "CustomResourceDefinitionVersion describes a version for CRD.",
     "required": [
      "name",
      "served",
@@ -92273,6 +92294,45 @@
    "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.JSONSchemaPropsOrStringArray": {
     "description": "JSONSchemaPropsOrStringArray represents a JSONSchemaProps or a string array."
    },
+   "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.ServiceReference": {
+    "description": "ServiceReference holds a reference to Service.legacy.k8s.io",
+    "required": [
+     "namespace",
+     "name"
+    ],
+    "properties": {
+     "name": {
+      "description": "`name` is the name of the service. Required",
+      "type": "string"
+     },
+     "namespace": {
+      "description": "`namespace` is the namespace of the service. Required",
+      "type": "string"
+     },
+     "path": {
+      "description": "`path` is an optional URL path which will be sent in any request to this service.",
+      "type": "string"
+     }
+    }
+   },
+   "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.WebhookClientConfig": {
+    "description": "WebhookClientConfig contains the information to make a TLS connection with the webhook. It has the same field as admissionregistration.v1beta1.WebhookClientConfig.",
+    "properties": {
+     "caBundle": {
+      "description": "`caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate. If unspecified, system trust roots on the apiserver are used.",
+      "type": "string",
+      "format": "byte"
+     },
+     "service": {
+      "description": "`service` is a reference to the service for this webhook. Either `service` or `url` must be specified.\n\nIf the webhook is running within the cluster, then you should use `service`.\n\nPort 443 will be used if it is open, otherwise it is an error.",
+      "$ref": "#/definitions/io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.ServiceReference"
+     },
+     "url": {
+      "description": "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
+      "type": "string"
+     }
+    }
+   },
    "io.k8s.apimachinery.pkg.api.resource.Quantity": {
     "description": "Quantity is a fixed-point representation of a number. It provides convenient marshaling/unmarshaling in JSON and YAML, in addition to String() and Int64() accessors.\n\nThe serialization format is:\n\n\u003cquantity\u003e        ::= \u003csignedNumber\u003e\u003csuffix\u003e\n  (Note that \u003csuffix\u003e may be empty, from the \"\" case in \u003cdecimalSI\u003e.)\n\u003cdigit\u003e           ::= 0 | 1 | ... | 9 \u003cdigits\u003e          ::= \u003cdigit\u003e | \u003cdigit\u003e\u003cdigits\u003e \u003cnumber\u003e          ::= \u003cdigits\u003e | \u003cdigits\u003e.\u003cdigits\u003e | \u003cdigits\u003e. | .\u003cdigits\u003e \u003csign\u003e            ::= \"+\" | \"-\" \u003csignedNumber\u003e    ::= \u003cnumber\u003e | \u003csign\u003e\u003cnumber\u003e \u003csuffix\u003e          ::= \u003cbinarySI\u003e | \u003cdecimalExponent\u003e | \u003cdecimalSI\u003e \u003cbinarySI\u003e        ::= Ki | Mi | Gi | Ti | Pi | Ei\n  (International System of units; See: http://physics.nist.gov/cuu/Units/binary.html)\n\u003cdecimalSI\u003e       ::= m | \"\" | k | M | G | T | P | E\n  (Note that 1024 = 1Ki but 1000 = 1k; I didn't choose the capitalization.)\n\u003cdecimalExponent\u003e ::= \"e\" \u003csignedNumber\u003e | \"E\" \u003csignedNumber\u003e\n\nNo matter which of the three exponent forms is used, no quantity may represent a number greater than 2^63-1 in magnitude, nor may it have more than 3 decimal places. Numbers larger or more precise will be capped or rounded up. (E.g.: 0.1m will rounded up to 1m.) This may be extended in the future if we require larger or smaller quantities.\n\nWhen a Quantity is parsed from a string, it will remember the type of suffix it had, and will use the same type again when it is serialized.\n\nBefore serializing, Quantity will be put in \"canonical form\". This means that Exponent/suffix will be adjusted up or down (with a corresponding increase or decrease in Mantissa) such that:\n  a. No precision is lost\n  b. No fractional digits will be emitted\n  c. The exponent (or suffix) is as large as possible.\nThe sign will be omitted unless the number is negative.\n\nExamples:\n  1.5 will be serialized as \"1500m\"\n  1.5Gi will be serialized as \"1536Mi\"\n\nNote that the quantity will NEVER be internally represented by a floating point number. That is the whole point of this exercise.\n\nNon-canonical values will still parse as long as they are well formed, but will be re-emitted in their canonical form. (So always use canonical form, or don't diff.)\n\nThis format is intended to make it difficult to use these numbers without writing some sort of special handling code in the hopes that that will cause implementors to also use a fixed point implementation.",
     "type": "string"

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

@@ -1863,7 +1863,7 @@
     "properties": {
      "url": {
       "type": "string",
-      "description": "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either."
+      "description": "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either."
      },
      "service": {
       "$ref": "v1beta1.ServiceReference",

api/swagger-spec/auditregistration.k8s.io_v1alpha1.json

@@ -1158,7 +1158,7 @@
     "properties": {
      "url": {
       "type": "string",
-      "description": "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either."
+      "description": "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either."
      },
      "service": {
       "$ref": "v1alpha1.ServiceReference",

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

@@ -1591,7 +1591,7 @@ When an object is created, the system will populate this list with the current s
 <tbody>
 <tr>
 <td class="tableblock halign-left valign-top"><p class="tableblock">url</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code>url</code> gives the location of the webhook, in standard URL form (<code>[scheme://]host:port/path</code>). Exactly one of <code>url</code> or <code>service</code> must be specified.<br>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code>url</code> gives the location of the webhook, in standard URL form (<code>scheme://host:port/path</code>). Exactly one of <code>url</code> or <code>service</code> must be specified.<br>
 <br>
 The <code>host</code> should not refer to a service running in the cluster; use the <code>service</code> field instead. The host might be resolved via external DNS in some apiservers (e.g., <code>kube-apiserver</code> cannot resolve in-cluster DNS as that would be a layering violation). <code>host</code> may also be an IP address.<br>
 <br>

docs/api-reference/auditregistration.k8s.io/v1alpha1/definitions.html

@@ -503,7 +503,7 @@ span.icon > [class^="icon-"], span.icon > [class*=" icon-"] { cursor: default; }
 <tbody>
 <tr>
 <td class="tableblock halign-left valign-top"><p class="tableblock">url</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><code>url</code> gives the location of the webhook, in standard URL form (<code>[scheme://]host:port/path</code>). Exactly one of <code>url</code> or <code>service</code> must be specified.<br>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code>url</code> gives the location of the webhook, in standard URL form (<code>scheme://host:port/path</code>). Exactly one of <code>url</code> or <code>service</code> must be specified.<br>
 <br>
 The <code>host</code> should not refer to a service running in the cluster; use the <code>service</code> field instead. The host might be resolved via external DNS in some apiservers (e.g., <code>kube-apiserver</code> cannot resolve in-cluster DNS as that would be a layering violation). <code>host</code> may also be an IP address.<br>
 <br>

pkg/apis/admissionregistration/types.go

@@ -290,7 +290,7 @@ const (
 // connection with the webhook
 type WebhookClientConfig struct {
 	// `url` gives the location of the webhook, in standard URL form
-	// (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
 	// must be specified.
 	//
 	// The `host` should not refer to a service running in the cluster; use

pkg/apis/admissionregistration/validation/BUILD

@@ -27,6 +27,7 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/util/sets:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/validation:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/validation/field:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/webhook:go_default_library",
     ],
 )
 

pkg/apis/admissionregistration/validation/validation.go

@@ -18,7 +18,6 @@ package validation
 
 import (
 	"fmt"
-	"net/url"
 	"strings"
 
 	genericvalidation "k8s.io/apimachinery/pkg/api/validation"
@@ -26,6 +25,7 @@ import (
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/validation"
 	"k8s.io/apimachinery/pkg/util/validation/field"
+	"k8s.io/apiserver/pkg/util/webhook"
 	"k8s.io/kubernetes/pkg/apis/admissionregistration"
 )
 
@@ -200,93 +200,15 @@ func validateWebhook(hook *admissionregistration.Webhook, fldPath *field.Path) f
 		allErrors = append(allErrors, metav1validation.ValidateLabelSelector(hook.NamespaceSelector, fldPath.Child("namespaceSelector"))...)
 	}
 
-	allErrors = append(allErrors, validateWebhookClientConfig(fldPath.Child("clientConfig"), &hook.ClientConfig)...)
-
-	return allErrors
-}
-
-func validateWebhookClientConfig(fldPath *field.Path, cc *admissionregistration.WebhookClientConfig) field.ErrorList {
-	var allErrors field.ErrorList
-	if (cc.URL == nil) == (cc.Service == nil) {
-		allErrors = append(allErrors, field.Required(fldPath.Child("url"), "exactly one of url or service is required"))
+	cc := hook.ClientConfig
+	switch {
+	case (cc.URL == nil) == (cc.Service == nil):
+		allErrors = append(allErrors, field.Required(fldPath.Child("clientConfig"), "exactly one of url or service is required"))
+	case cc.URL != nil:
+		allErrors = append(allErrors, webhook.ValidateWebhookURL(fldPath.Child("clientConfig").Child("url"), *cc.URL, true)...)
+	case cc.Service != nil:
+		allErrors = append(allErrors, webhook.ValidateWebhookService(fldPath.Child("clientConfig").Child("service"), cc.Service.Name, cc.Service.Namespace, cc.Service.Path)...)
 	}
-
-	if cc.URL != nil {
-		const form = "; desired format: https://host[/path]"
-		if u, err := url.Parse(*cc.URL); err != nil {
-			allErrors = append(allErrors, field.Required(fldPath.Child("url"), "url must be a valid URL: "+err.Error()+form))
-		} else {
-			if u.Scheme != "https" {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.Scheme, "'https' is the only allowed URL scheme"+form))
-			}
-			if len(u.Host) == 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.Host, "host must be provided"+form))
-			}
-			if u.User != nil {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.User.String(), "user information is not permitted in the URL"))
-			}
-			if len(u.Fragment) != 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.Fragment, "fragments are not permitted in the URL"))
-			}
-			if len(u.RawQuery) != 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.RawQuery, "query parameters are not permitted in the URL"))
-			}
-		}
-	}
-
-	if cc.Service != nil {
-		allErrors = append(allErrors, validateWebhookService(fldPath.Child("service"), cc.Service)...)
-	}
-	return allErrors
-}
-
-// note: this has copy/paste inheritance in auditregistration
-func validateWebhookService(fldPath *field.Path, svc *admissionregistration.ServiceReference) field.ErrorList {
-	var allErrors field.ErrorList
-
-	if len(svc.Name) == 0 {
-		allErrors = append(allErrors, field.Required(fldPath.Child("name"), "service name is required"))
-	}
-
-	if len(svc.Namespace) == 0 {
-		allErrors = append(allErrors, field.Required(fldPath.Child("namespace"), "service namespace is required"))
-	}
-
-	if svc.Path == nil {
-		return allErrors
-	}
-
-	// TODO: replace below with url.Parse + verifying that host is empty?
-
-	urlPath := *svc.Path
-	if urlPath == "/" || len(urlPath) == 0 {
-		return allErrors
-	}
-	if urlPath == "//" {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "segment[0] may not be empty"))
-		return allErrors
-	}
-
-	if !strings.HasPrefix(urlPath, "/") {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "must start with a '/'"))
-	}
-
-	urlPathToCheck := urlPath[1:]
-	if strings.HasSuffix(urlPathToCheck, "/") {
-		urlPathToCheck = urlPathToCheck[:len(urlPathToCheck)-1]
-	}
-	steps := strings.Split(urlPathToCheck, "/")
-	for i, step := range steps {
-		if len(step) == 0 {
-			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d] may not be empty", i)))
-			continue
-		}
-		failures := validation.IsDNS1123Subdomain(step)
-		for _, failure := range failures {
-			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d]: %v", i, failure)))
-		}
-	}
-
 	return allErrors
 }
 

pkg/apis/admissionregistration/validation/validation_test.go

@@ -540,7 +540,7 @@ func TestValidateValidatingWebhookConfiguration(t *testing.T) {
 						},
 					},
 				}),
-			expectedError: `[0].clientConfig.url: Required value: exactly one of url or service is required`,
+			expectedError: `[0].clientConfig: Required value: exactly one of url or service is required`,
 		},
 		{
 			name: "blank URL",

pkg/apis/auditregistration/types.go

@@ -135,7 +135,7 @@ type WebhookThrottleConfig struct {
 // WebhookClientConfig contains the information to make a connection with the webhook
 type WebhookClientConfig struct {
 	// `url` gives the location of the webhook, in standard URL form
-	// (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
 	// must be specified.
 	//
 	// The `host` should not refer to a service running in the cluster; use

pkg/apis/auditregistration/validation/BUILD

@@ -9,8 +9,8 @@ go_library(
         "//pkg/apis/auditregistration:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/api/validation:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/sets:go_default_library",
-        "//staging/src/k8s.io/apimachinery/pkg/util/validation:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/validation/field:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/webhook:go_default_library",
     ],
 )
 

pkg/apis/auditregistration/validation/validation.go

@@ -17,14 +17,12 @@ limitations under the License.
 package validation
 
 import (
-	"fmt"
-	"net/url"
 	"strings"
 
 	genericvalidation "k8s.io/apimachinery/pkg/api/validation"
 	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/apimachinery/pkg/util/validation"
 	"k8s.io/apimachinery/pkg/util/validation/field"
+	"k8s.io/apiserver/pkg/util/webhook"
 	"k8s.io/kubernetes/pkg/apis/auditregistration"
 )
 
@@ -49,7 +47,16 @@ func ValidateWebhook(w auditregistration.Webhook, fldPath *field.Path) field.Err
 	if w.Throttle != nil {
 		allErrs = append(allErrs, ValidateWebhookThrottleConfig(w.Throttle, fldPath.Child("throttle"))...)
 	}
-	allErrs = append(allErrs, ValidateWebhookClientConfig(&w.ClientConfig, fldPath.Child("clientConfig"))...)
+
+	cc := w.ClientConfig
+	switch {
+	case (cc.URL == nil) == (cc.Service == nil):
+		allErrs = append(allErrs, field.Required(fldPath.Child("clientConfig"), "exactly one of url or service is required"))
+	case cc.URL != nil:
+		allErrs = append(allErrs, webhook.ValidateWebhookURL(fldPath.Child("clientConfig").Child("url"), *cc.URL, false)...)
+	case cc.Service != nil:
+		allErrs = append(allErrs, webhook.ValidateWebhookService(fldPath.Child("clientConfig").Child("service"), cc.Service.Name, cc.Service.Namespace, cc.Service.Path)...)
+	}
 	return allErrs
 }
 
@@ -65,90 +72,6 @@ func ValidateWebhookThrottleConfig(c *auditregistration.WebhookThrottleConfig, f
 	return allErrs
 }
 
-// ValidateWebhookClientConfig validates the WebhookClientConfig
-// note: this is largely copy/paste inheritance from admissionregistration with subtle changes
-func ValidateWebhookClientConfig(cc *auditregistration.WebhookClientConfig, fldPath *field.Path) field.ErrorList {
-	var allErrors field.ErrorList
-	if (cc.URL == nil) == (cc.Service == nil) {
-		allErrors = append(allErrors, field.Required(fldPath.Child("url"), "exactly one of url or service is required"))
-	}
-
-	if cc.URL != nil {
-		const form = "; desired format: https://host[/path]"
-		if u, err := url.Parse(*cc.URL); err != nil {
-			allErrors = append(allErrors, field.Required(fldPath.Child("url"), "url must be a valid URL: "+err.Error()+form))
-		} else {
-			if len(u.Host) == 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.Host, "host must be provided"+form))
-			}
-			if u.User != nil {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.User.String(), "user information is not permitted in the URL"))
-			}
-			if len(u.Fragment) != 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.Fragment, "fragments are not permitted in the URL"))
-			}
-			if len(u.RawQuery) != 0 {
-				allErrors = append(allErrors, field.Invalid(fldPath.Child("url"), u.RawQuery, "query parameters are not permitted in the URL"))
-			}
-		}
-	}
-
-	if cc.Service != nil {
-		allErrors = append(allErrors, validateWebhookService(cc.Service, fldPath.Child("service"))...)
-	}
-	return allErrors
-}
-
-// note: this is copy/paste inheritance from admissionregistration
-func validateWebhookService(svc *auditregistration.ServiceReference, fldPath *field.Path) field.ErrorList {
-	var allErrors field.ErrorList
-
-	if len(svc.Name) == 0 {
-		allErrors = append(allErrors, field.Required(fldPath.Child("name"), "service name is required"))
-	}
-
-	if len(svc.Namespace) == 0 {
-		allErrors = append(allErrors, field.Required(fldPath.Child("namespace"), "service namespace is required"))
-	}
-
-	if svc.Path == nil {
-		return allErrors
-	}
-
-	// TODO: replace below with url.Parse + verifying that host is empty?
-
-	urlPath := *svc.Path
-	if urlPath == "/" || len(urlPath) == 0 {
-		return allErrors
-	}
-	if urlPath == "//" {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "segment[0] may not be empty"))
-		return allErrors
-	}
-
-	if !strings.HasPrefix(urlPath, "/") {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "must start with a '/'"))
-	}
-
-	urlPathToCheck := urlPath[1:]
-	if strings.HasSuffix(urlPathToCheck, "/") {
-		urlPathToCheck = urlPathToCheck[:len(urlPathToCheck)-1]
-	}
-	steps := strings.Split(urlPathToCheck, "/")
-	for i, step := range steps {
-		if len(step) == 0 {
-			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d] may not be empty", i)))
-			continue
-		}
-		failures := validation.IsDNS1123Subdomain(step)
-		for _, failure := range failures {
-			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d]: %v", i, failure)))
-		}
-	}
-
-	return allErrors
-}
-
 // ValidatePolicy validates the audit policy
 func ValidatePolicy(policy auditregistration.Policy, fldPath *field.Path) field.ErrorList {
 	var allErrs field.ErrorList

pkg/apis/auditregistration/validation/validation_test.go

@@ -159,7 +159,7 @@ func TestValidateWebhookConfiguration(t *testing.T) {
 					URL: strPtr("example.com/k8s/webhook"),
 				},
 			},
-			expectedError: `webhook.clientConfig.url: Required value: exactly one of url or service is required`,
+			expectedError: `webhook.clientConfig: Required value: exactly one of url or service is required`,
 		},
 		{
 			name: "blank URL",

pkg/features/kube_features.go

@@ -456,8 +456,9 @@ var defaultKubernetesFeatureGates = map[utilfeature.Feature]utilfeature.FeatureS
 
 	// inherited features from apiextensions-apiserver, relisted here to get a conflict if it is changed
 	// unintentionally on either side:
-	apiextensionsfeatures.CustomResourceValidation:   {Default: true, PreRelease: utilfeature.Beta},
-	apiextensionsfeatures.CustomResourceSubresources: {Default: true, PreRelease: utilfeature.Beta},
+	apiextensionsfeatures.CustomResourceValidation:        {Default: true, PreRelease: utilfeature.Beta},
+	apiextensionsfeatures.CustomResourceSubresources:      {Default: true, PreRelease: utilfeature.Beta},
+	apiextensionsfeatures.CustomResourceWebhookConversion: {Default: false, PreRelease: utilfeature.Alpha},
 
 	// features that enable backwards compatibility but are scheduled to be removed
 	// ...

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

@@ -223,7 +223,7 @@ message Webhook {
 // connection with the webhook
 message WebhookClientConfig {
   // `url` gives the location of the webhook, in standard URL form
-  // (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+  // (`scheme://host:port/path`). Exactly one of `url` or `service`
   // must be specified.
   //
   // The `host` should not refer to a service running in the cluster; use

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

@@ -246,7 +246,7 @@ const (
 // connection with the webhook
 type WebhookClientConfig struct {
 	// `url` gives the location of the webhook, in standard URL form
-	// (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
 	// must be specified.
 	//
 	// The `host` should not refer to a service running in the cluster; use

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

@@ -114,7 +114,7 @@ func (Webhook) SwaggerDoc() map[string]string {
 
 var map_WebhookClientConfig = map[string]string{
 	"":         "WebhookClientConfig contains the information to make a TLS connection with the webhook",
-	"url":      "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
+	"url":      "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
 	"service":  "`service` is a reference to the service for this webhook. Either `service` or `url` must be specified.\n\nIf the webhook is running within the cluster, then you should use `service`.\n\nPort 443 will be used if it is open, otherwise it is an error.",
 	"caBundle": "`caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate. If unspecified, system trust roots on the apiserver are used.",
 }

staging/src/k8s.io/api/auditregistration/v1alpha1/generated.proto

@@ -99,7 +99,7 @@ message Webhook {
 // WebhookClientConfig contains the information to make a connection with the webhook
 message WebhookClientConfig {
   // `url` gives the location of the webhook, in standard URL form
-  // (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+  // (`scheme://host:port/path`). Exactly one of `url` or `service`
   // must be specified.
   //
   // The `host` should not refer to a service running in the cluster; use

staging/src/k8s.io/api/auditregistration/v1alpha1/types.go

@@ -133,7 +133,7 @@ type WebhookThrottleConfig struct {
 // WebhookClientConfig contains the information to make a connection with the webhook
 type WebhookClientConfig struct {
 	// `url` gives the location of the webhook, in standard URL form
-	// (`[scheme://]host:port/path`). Exactly one of `url` or `service`
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
 	// must be specified.
 	//
 	// The `host` should not refer to a service running in the cluster; use

staging/src/k8s.io/api/auditregistration/v1alpha1/types_swagger_doc_generated.go

@@ -88,7 +88,7 @@ func (Webhook) SwaggerDoc() map[string]string {
 
 var map_WebhookClientConfig = map[string]string{
 	"":         "WebhookClientConfig contains the information to make a connection with the webhook",
-	"url":      "`url` gives the location of the webhook, in standard URL form (`[scheme://]host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
+	"url":      "`url` gives the location of the webhook, in standard URL form (`scheme://host:port/path`). Exactly one of `url` or `service` must be specified.\n\nThe `host` should not refer to a service running in the cluster; use the `service` field instead. The host might be resolved via external DNS in some apiservers (e.g., `kube-apiserver` cannot resolve in-cluster DNS as that would be a layering violation). `host` may also be an IP address.\n\nPlease note that using `localhost` or `127.0.0.1` as a `host` is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.\n\nThe scheme must be \"https\"; the URL must begin with \"https://\".\n\nA path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.\n\nAttempting to use a user or basic auth e.g. \"user:password@\" is not allowed. Fragments (\"#...\") and query parameters (\"?...\") are not allowed, either.",
 	"service":  "`service` is a reference to the service for this webhook. Either `service` or `url` must be specified.\n\nIf the webhook is running within the cluster, then you should use `service`.\n\nPort 443 will be used if it is open, otherwise it is an error.",
 	"caBundle": "`caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate. If unspecified, system trust roots on the apiserver are used.",
 }

staging/src/k8s.io/apiextensions-apiserver/Godeps/Godeps.json

@@ -2427,6 +2427,10 @@
 			"Rev": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
 		},
 		{
+			"ImportPath": "k8s.io/apiserver/pkg/util/webhook",
+			"Rev": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+		},
+		{
 			"ImportPath": "k8s.io/client-go/discovery",
 			"Rev": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
 		},

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/fuzzer/fuzzer.go

@@ -61,6 +61,11 @@ func Funcs(codecs runtimeserializer.CodecFactory) []interface{} {
 					{Name: "Age", Type: "date", Description: swaggerMetadataDescriptions["creationTimestamp"], JSONPath: ".metadata.creationTimestamp"},
 				}
 			}
+			if obj.Conversion == nil {
+				obj.Conversion = &apiextensions.CustomResourceConversion{
+					Strategy: apiextensions.NoneConverter,
+				}
+			}
 		},
 		func(obj *apiextensions.CustomResourceDefinition, c fuzz.Continue) {
 			c.FuzzNoCustom(obj)

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go

@@ -20,6 +20,16 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
+// ConversionStrategyType describes different conversion types.
+type ConversionStrategyType string
+
+const (
+	// NoneConverter is a converter that only sets apiversion of the CR and leave everything else unchanged.
+	NoneConverter ConversionStrategyType = "None"
+	// WebhookConverter is a converter that calls to an external webhook to convert the CR.
+	WebhookConverter ConversionStrategyType = "Webhook"
+)
+
 // CustomResourceDefinitionSpec describes how a user wants their resource to appear
 type CustomResourceDefinitionSpec struct {
 	// Group is the group this resource belongs in
@@ -51,8 +61,86 @@ type CustomResourceDefinitionSpec struct {
 	Versions []CustomResourceDefinitionVersion
 	// AdditionalPrinterColumns are additional columns shown e.g. in kubectl next to the name. Defaults to a created-at column.
 	AdditionalPrinterColumns []CustomResourceColumnDefinition
+
+	// `conversion` defines conversion settings for the CRD.
+	Conversion *CustomResourceConversion
+}
+
+// CustomResourceConversion describes how to convert different versions of a CR.
+type CustomResourceConversion struct {
+	// `strategy` specifies the conversion strategy. Allowed values are:
+	// - `None`: The converter only change the apiVersion and would not touch any other field in the CR.
+	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.
+	Strategy ConversionStrategyType
+
+	// `webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`.
+	WebhookClientConfig *WebhookClientConfig
+}
+
+// WebhookClientConfig contains the information to make a TLS
+// connection with the webhook. It has the same field as admissionregistration.internal.WebhookClientConfig.
+type WebhookClientConfig struct {
+	// `url` gives the location of the webhook, in standard URL form
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
+	// must be specified.
+	//
+	// The `host` should not refer to a service running in the cluster; use
+	// the `service` field instead. The host might be resolved via external
+	// DNS in some apiservers (e.g., `kube-apiserver` cannot resolve
+	// in-cluster DNS as that would be a layering violation). `host` may
+	// also be an IP address.
+	//
+	// Please note that using `localhost` or `127.0.0.1` as a `host` is
+	// risky unless you take great care to run this webhook on all hosts
+	// which run an apiserver which might need to make calls to this
+	// webhook. Such installs are likely to be non-portable, i.e., not easy
+	// to turn up in a new cluster.
+	//
+	// The scheme must be "https"; the URL must begin with "https://".
+	//
+	// A path is optional, and if present may be any string permissible in
+	// a URL. You may use the path to pass an arbitrary string to the
+	// webhook, for example, a cluster identifier.
+	//
+	// Attempting to use a user or basic auth e.g. "user:password@" is not
+	// allowed. Fragments ("#...") and query parameters ("?...") are not
+	// allowed, either.
+	//
+	// +optional
+	URL *string
+
+	// `service` is a reference to the service for this webhook. Either
+	// `service` or `url` must be specified.
+	//
+	// If the webhook is running within the cluster, then you should use `service`.
+	//
+	// Port 443 will be used if it is open, otherwise it is an error.
+	//
+	// +optional
+	Service *ServiceReference
+
+	// `caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate.
+	// If unspecified, system trust roots on the apiserver are used.
+	// +optional
+	CABundle []byte
+}
+
+// ServiceReference holds a reference to Service.legacy.k8s.io
+type ServiceReference struct {
+	// `namespace` is the namespace of the service.
+	// Required
+	Namespace string
+	// `name` is the name of the service.
+	// Required
+	Name string
+
+	// `path` is an optional URL path which will be sent in any request to
+	// this service.
+	// +optional
+	Path *string
 }
 
+// CustomResourceDefinitionVersion describes a version for CRD.
 type CustomResourceDefinitionVersion struct {
 	// Name is the version name, e.g. “v1”, “v2beta1”, etc.
 	Name string

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/BUILD

@@ -30,6 +30,7 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/conversion:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/runtime:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/types:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/json:go_default_library",
         "//vendor/github.com/gogo/protobuf/proto:go_default_library",
         "//vendor/github.com/gogo/protobuf/sortkeys:go_default_library",

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/defaults.go

@@ -71,4 +71,9 @@ func SetDefaults_CustomResourceDefinitionSpec(obj *CustomResourceDefinitionSpec)
 			{Name: "Age", Type: "date", Description: swaggerMetadataDescriptions["creationTimestamp"], JSONPath: ".metadata.creationTimestamp"},
 		}
 	}
+	if obj.Conversion == nil {
+		obj.Conversion = &CustomResourceConversion{
+			Strategy: NoneConverter,
+		}
+	}
 }

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/generated.proto

@@ -28,6 +28,51 @@ import "k8s.io/apimachinery/pkg/runtime/schema/generated.proto";
 // Package-wide variables from generator "generated".
 option go_package = "v1beta1";
 
+// ConversionRequest describes the conversion request parameters.
+message ConversionRequest {
+  // `uid` is an identifier for the individual request/response. It allows us to distinguish instances of requests which are
+  // otherwise identical (parallel requests, requests when earlier requests did not modify etc)
+  // The UID is meant to track the round trip (request/response) between the KAS and the WebHook, not the user request.
+  // It is suitable for correlating log entries between the webhook and apiserver, for either auditing or debugging.
+  optional string uid = 1;
+
+  // `desiredAPIVersion` is the version to convert given objects to. e.g. "myapi.example.com/v1"
+  optional string desiredAPIVersion = 2;
+
+  // `objects` is the list of CR objects to be converted.
+  repeated k8s.io.apimachinery.pkg.runtime.RawExtension objects = 3;
+}
+
+// ConversionResponse describes a conversion response.
+message ConversionResponse {
+  // `uid` is an identifier for the individual request/response.
+  // This should be copied over from the corresponding AdmissionRequest.
+  optional string uid = 1;
+
+  // `convertedObjects` is the list of converted version of `request.objects` if the `result` is successful otherwise empty.
+  // The webhook is expected to set apiVersion of these objects to the ConversionRequest.desiredAPIVersion. The list
+  // must also has the same size as input list with the same objects in the same order(i.e. equal UIDs and object meta)
+  repeated k8s.io.apimachinery.pkg.runtime.RawExtension convertedObjects = 2;
+
+  // `result` contains the result of conversion with extra details if the conversion failed. `result.status` determines if
+  // the conversion failed or succeeded. The `result.status` field is required and represent the success or failure of the
+  // conversion. A successful conversion must set `result.status` to `Success`. A failed conversion must set
+  // `result.status` to `Failure` and provide more details in `result.message` and return http status 200. The `result.message`
+  // will be used to construct an error message for the end user.
+  optional k8s.io.apimachinery.pkg.apis.meta.v1.Status result = 3;
+}
+
+// ConversionReview describes a conversion request/response.
+message ConversionReview {
+  // `request` describes the attributes for the conversion request.
+  // +optional
+  optional ConversionRequest request = 1;
+
+  // `response` describes the attributes for the conversion response.
+  // +optional
+  optional ConversionResponse response = 2;
+}
+
 // CustomResourceColumnDefinition specifies a column for server side printing.
 message CustomResourceColumnDefinition {
   // name is a human readable name for the column.
@@ -57,6 +102,19 @@ message CustomResourceColumnDefinition {
   optional string JSONPath = 6;
 }
 
+// CustomResourceConversion describes how to convert different versions of a CR.
+message CustomResourceConversion {
+  // `strategy` specifies the conversion strategy. Allowed values are:
+  // - `None`: The converter only change the apiVersion and would not touch any other field in the CR.
+  // - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.
+  optional string strategy = 1;
+
+  // `webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`. This field is
+  // alpha-level and is only honored by servers that enable the CustomResourceWebhookConversion feature.
+  // +optional
+  optional WebhookClientConfig webhookClientConfig = 2;
+}
+
 // CustomResourceDefinition represents a resource that should be exposed on the API server.  Its name MUST be in the format
 // <.spec.name>.<.spec.group>.
 message CustomResourceDefinition {
@@ -169,6 +227,10 @@ message CustomResourceDefinitionSpec {
   // AdditionalPrinterColumns are additional columns shown e.g. in kubectl next to the name. Defaults to a created-at column.
   // +optional
   repeated CustomResourceColumnDefinition additionalPrinterColumns = 8;
+
+  // `conversion` defines conversion settings for the CRD.
+  // +optional
+  optional CustomResourceConversion conversion = 9;
 }
 
 // CustomResourceDefinitionStatus indicates the state of the CustomResourceDefinition
@@ -189,6 +251,7 @@ message CustomResourceDefinitionStatus {
   repeated string storedVersions = 3;
 }
 
+// CustomResourceDefinitionVersion describes a version for CRD.
 message CustomResourceDefinitionVersion {
   // Name is the version name, e.g. “v1”, “v2beta1”, etc.
   optional string name = 1;
@@ -363,3 +426,67 @@ message JSONSchemaPropsOrStringArray {
   repeated string property = 2;
 }
 
+// ServiceReference holds a reference to Service.legacy.k8s.io
+message ServiceReference {
+  // `namespace` is the namespace of the service.
+  // Required
+  optional string namespace = 1;
+
+  // `name` is the name of the service.
+  // Required
+  optional string name = 2;
+
+  // `path` is an optional URL path which will be sent in any request to
+  // this service.
+  // +optional
+  optional string path = 3;
+}
+
+// WebhookClientConfig contains the information to make a TLS
+// connection with the webhook. It has the same field as admissionregistration.v1beta1.WebhookClientConfig.
+message WebhookClientConfig {
+  // `url` gives the location of the webhook, in standard URL form
+  // (`scheme://host:port/path`). Exactly one of `url` or `service`
+  // must be specified.
+  //
+  // The `host` should not refer to a service running in the cluster; use
+  // the `service` field instead. The host might be resolved via external
+  // DNS in some apiservers (e.g., `kube-apiserver` cannot resolve
+  // in-cluster DNS as that would be a layering violation). `host` may
+  // also be an IP address.
+  //
+  // Please note that using `localhost` or `127.0.0.1` as a `host` is
+  // risky unless you take great care to run this webhook on all hosts
+  // which run an apiserver which might need to make calls to this
+  // webhook. Such installs are likely to be non-portable, i.e., not easy
+  // to turn up in a new cluster.
+  //
+  // The scheme must be "https"; the URL must begin with "https://".
+  //
+  // A path is optional, and if present may be any string permissible in
+  // a URL. You may use the path to pass an arbitrary string to the
+  // webhook, for example, a cluster identifier.
+  //
+  // Attempting to use a user or basic auth e.g. "user:password@" is not
+  // allowed. Fragments ("#...") and query parameters ("?...") are not
+  // allowed, either.
+  //
+  // +optional
+  optional string url = 3;
+
+  // `service` is a reference to the service for this webhook. Either
+  // `service` or `url` must be specified.
+  //
+  // If the webhook is running within the cluster, then you should use `service`.
+  //
+  // Port 443 will be used if it is open, otherwise it is an error.
+  //
+  // +optional
+  optional ServiceReference service = 1;
+
+  // `caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate.
+  // If unspecified, system trust roots on the apiserver are used.
+  // +optional
+  optional bytes caBundle = 2;
+}
+

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/register.go

@@ -48,6 +48,7 @@ func addKnownTypes(scheme *runtime.Scheme) error {
 	scheme.AddKnownTypes(SchemeGroupVersion,
 		&CustomResourceDefinition{},
 		&CustomResourceDefinitionList{},
+		&ConversionReview{},
 	)
 	metav1.AddToGroupVersion(scheme, SchemeGroupVersion)
 	return nil

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go

@@ -18,6 +18,18 @@ package v1beta1
 
 import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+)
+
+// ConversionStrategyType describes different conversion types.
+type ConversionStrategyType string
+
+const (
+	// NoneConverter is a converter that only sets apiversion of the CR and leave everything else unchanged.
+	NoneConverter ConversionStrategyType = "None"
+	// WebhookConverter is a converter that calls to an external webhook to convert the CR.
+	WebhookConverter ConversionStrategyType = "Webhook"
 )
 
 // CustomResourceDefinitionSpec describes how a user wants their resource to appear
@@ -56,8 +68,89 @@ type CustomResourceDefinitionSpec struct {
 	// AdditionalPrinterColumns are additional columns shown e.g. in kubectl next to the name. Defaults to a created-at column.
 	// +optional
 	AdditionalPrinterColumns []CustomResourceColumnDefinition `json:"additionalPrinterColumns,omitempty" protobuf:"bytes,8,rep,name=additionalPrinterColumns"`
+
+	// `conversion` defines conversion settings for the CRD.
+	// +optional
+	Conversion *CustomResourceConversion `json:"conversion,omitempty" protobuf:"bytes,9,opt,name=conversion"`
+}
+
+// CustomResourceConversion describes how to convert different versions of a CR.
+type CustomResourceConversion struct {
+	// `strategy` specifies the conversion strategy. Allowed values are:
+	// - `None`: The converter only change the apiVersion and would not touch any other field in the CR.
+	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.
+	Strategy ConversionStrategyType `json:"strategy" protobuf:"bytes,1,name=strategy"`
+
+	// `webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`. This field is
+	// alpha-level and is only honored by servers that enable the CustomResourceWebhookConversion feature.
+	// +optional
+	WebhookClientConfig *WebhookClientConfig `json:"webhookClientConfig,omitempty" protobuf:"bytes,2,name=webhookClientConfig"`
+}
+
+// WebhookClientConfig contains the information to make a TLS
+// connection with the webhook. It has the same field as admissionregistration.v1beta1.WebhookClientConfig.
+type WebhookClientConfig struct {
+	// `url` gives the location of the webhook, in standard URL form
+	// (`scheme://host:port/path`). Exactly one of `url` or `service`
+	// must be specified.
+	//
+	// The `host` should not refer to a service running in the cluster; use
+	// the `service` field instead. The host might be resolved via external
+	// DNS in some apiservers (e.g., `kube-apiserver` cannot resolve
+	// in-cluster DNS as that would be a layering violation). `host` may
+	// also be an IP address.
+	//
+	// Please note that using `localhost` or `127.0.0.1` as a `host` is
+	// risky unless you take great care to run this webhook on all hosts
+	// which run an apiserver which might need to make calls to this
+	// webhook. Such installs are likely to be non-portable, i.e., not easy
+	// to turn up in a new cluster.
+	//
+	// The scheme must be "https"; the URL must begin with "https://".
+	//
+	// A path is optional, and if present may be any string permissible in
+	// a URL. You may use the path to pass an arbitrary string to the
+	// webhook, for example, a cluster identifier.
+	//
+	// Attempting to use a user or basic auth e.g. "user:password@" is not
+	// allowed. Fragments ("#...") and query parameters ("?...") are not
+	// allowed, either.
+	//
+	// +optional
+	URL *string `json:"url,omitempty" protobuf:"bytes,3,opt,name=url"`
+
+	// `service` is a reference to the service for this webhook. Either
+	// `service` or `url` must be specified.
+	//
+	// If the webhook is running within the cluster, then you should use `service`.
+	//
+	// Port 443 will be used if it is open, otherwise it is an error.
+	//
+	// +optional
+	Service *ServiceReference `json:"service,omitempty" protobuf:"bytes,1,opt,name=service"`
+
+	// `caBundle` is a PEM encoded CA bundle which will be used to validate the webhook's server certificate.
+	// If unspecified, system trust roots on the apiserver are used.
+	// +optional
+	CABundle []byte `json:"caBundle,omitempty" protobuf:"bytes,2,opt,name=caBundle"`
+}
+
+// ServiceReference holds a reference to Service.legacy.k8s.io
+type ServiceReference struct {
+	// `namespace` is the namespace of the service.
+	// Required
+	Namespace string `json:"namespace" protobuf:"bytes,1,opt,name=namespace"`
+	// `name` is the name of the service.
+	// Required
+	Name string `json:"name" protobuf:"bytes,2,opt,name=name"`
+
+	// `path` is an optional URL path which will be sent in any request to
+	// this service.
+	// +optional
+	Path *string `json:"path,omitempty" protobuf:"bytes,3,opt,name=path"`
 }
 
+// CustomResourceDefinitionVersion describes a version for CRD.
 type CustomResourceDefinitionVersion struct {
 	// Name is the version name, e.g. “v1”, “v2beta1”, etc.
 	Name string `json:"name" protobuf:"bytes,1,opt,name=name"`
@@ -263,3 +356,46 @@ type CustomResourceSubresourceScale struct {
 	// +optional
 	LabelSelectorPath *string `json:"labelSelectorPath,omitempty" protobuf:"bytes,3,opt,name=labelSelectorPath"`
 }
+
+// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
+
+// ConversionReview describes a conversion request/response.
+type ConversionReview struct {
+	metav1.TypeMeta `json:",inline"`
+	// `request` describes the attributes for the conversion request.
+	// +optional
+	Request *ConversionRequest `json:"request,omitempty" protobuf:"bytes,1,opt,name=request"`
+	// `response` describes the attributes for the conversion response.
+	// +optional
+	Response *ConversionResponse `json:"response,omitempty" protobuf:"bytes,2,opt,name=response"`
+}
+
+// ConversionRequest describes the conversion request parameters.
+type ConversionRequest struct {
+	// `uid` is an identifier for the individual request/response. It allows us to distinguish instances of requests which are
+	// otherwise identical (parallel requests, requests when earlier requests did not modify etc)
+	// The UID is meant to track the round trip (request/response) between the KAS and the WebHook, not the user request.
+	// It is suitable for correlating log entries between the webhook and apiserver, for either auditing or debugging.
+	UID types.UID `json:"uid" protobuf:"bytes,1,name=uid"`
+	// `desiredAPIVersion` is the version to convert given objects to. e.g. "myapi.example.com/v1"
+	DesiredAPIVersion string `json:"desiredAPIVersion" protobuf:"bytes,2,name=desiredAPIVersion"`
+	// `objects` is the list of CR objects to be converted.
+	Objects []runtime.RawExtension `json:"objects" protobuf:"bytes,3,rep,name=objects"`
+}
+
+// ConversionResponse describes a conversion response.
+type ConversionResponse struct {
+	// `uid` is an identifier for the individual request/response.
+	// This should be copied over from the corresponding AdmissionRequest.
+	UID types.UID `json:"uid" protobuf:"bytes,1,name=uid"`
+	// `convertedObjects` is the list of converted version of `request.objects` if the `result` is successful otherwise empty.
+	// The webhook is expected to set apiVersion of these objects to the ConversionRequest.desiredAPIVersion. The list
+	// must also has the same size as input list with the same objects in the same order(i.e. equal UIDs and object meta)
+	ConvertedObjects []runtime.RawExtension `json:"convertedObjects" protobuf:"bytes,2,rep,name=convertedObjects"`
+	// `result` contains the result of conversion with extra details if the conversion failed. `result.status` determines if
+	// the conversion failed or succeeded. The `result.status` field is required and represent the success or failure of the
+	// conversion. A successful conversion must set `result.status` to `Success`. A failed conversion must set
+	// `result.status` to `Failure` and provide more details in `result.message` and return http status 200. The `result.message`
+	// will be used to construct an error message for the end user.
+	Result metav1.Status `json:"result" protobuf:"bytes,3,name=result"`
+}

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/zz_generated.conversion.go

@@ -45,6 +45,16 @@ func RegisterConversions(s *runtime.Scheme) error {
 	}); err != nil {
 		return err
 	}
+	if err := s.AddGeneratedConversionFunc((*CustomResourceConversion)(nil), (*apiextensions.CustomResourceConversion)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_v1beta1_CustomResourceConversion_To_apiextensions_CustomResourceConversion(a.(*CustomResourceConversion), b.(*apiextensions.CustomResourceConversion), scope)
+	}); err != nil {
+		return err
+	}
+	if err := s.AddGeneratedConversionFunc((*apiextensions.CustomResourceConversion)(nil), (*CustomResourceConversion)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_apiextensions_CustomResourceConversion_To_v1beta1_CustomResourceConversion(a.(*apiextensions.CustomResourceConversion), b.(*CustomResourceConversion), scope)
+	}); err != nil {
+		return err
+	}
 	if err := s.AddGeneratedConversionFunc((*CustomResourceDefinition)(nil), (*apiextensions.CustomResourceDefinition)(nil), func(a, b interface{}, scope conversion.Scope) error {
 		return Convert_v1beta1_CustomResourceDefinition_To_apiextensions_CustomResourceDefinition(a.(*CustomResourceDefinition), b.(*apiextensions.CustomResourceDefinition), scope)
 	}); err != nil {
@@ -215,6 +225,26 @@ func RegisterConversions(s *runtime.Scheme) error {
 	}); err != nil {
 		return err
 	}
+	if err := s.AddGeneratedConversionFunc((*ServiceReference)(nil), (*apiextensions.ServiceReference)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_v1beta1_ServiceReference_To_apiextensions_ServiceReference(a.(*ServiceReference), b.(*apiextensions.ServiceReference), scope)
+	}); err != nil {
+		return err
+	}
+	if err := s.AddGeneratedConversionFunc((*apiextensions.ServiceReference)(nil), (*ServiceReference)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_apiextensions_ServiceReference_To_v1beta1_ServiceReference(a.(*apiextensions.ServiceReference), b.(*ServiceReference), scope)
+	}); err != nil {
+		return err
+	}
+	if err := s.AddGeneratedConversionFunc((*WebhookClientConfig)(nil), (*apiextensions.WebhookClientConfig)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_v1beta1_WebhookClientConfig_To_apiextensions_WebhookClientConfig(a.(*WebhookClientConfig), b.(*apiextensions.WebhookClientConfig), scope)
+	}); err != nil {
+		return err
+	}
+	if err := s.AddGeneratedConversionFunc((*apiextensions.WebhookClientConfig)(nil), (*WebhookClientConfig)(nil), func(a, b interface{}, scope conversion.Scope) error {
+		return Convert_apiextensions_WebhookClientConfig_To_v1beta1_WebhookClientConfig(a.(*apiextensions.WebhookClientConfig), b.(*WebhookClientConfig), scope)
+	}); err != nil {
+		return err
+	}
 	if err := s.AddConversionFunc((*apiextensions.JSONSchemaProps)(nil), (*JSONSchemaProps)(nil), func(a, b interface{}, scope conversion.Scope) error {
 		return Convert_apiextensions_JSONSchemaProps_To_v1beta1_JSONSchemaProps(a.(*apiextensions.JSONSchemaProps), b.(*JSONSchemaProps), scope)
 	}); err != nil {
@@ -263,6 +293,28 @@ func Convert_apiextensions_CustomResourceColumnDefinition_To_v1beta1_CustomResou
 	return autoConvert_apiextensions_CustomResourceColumnDefinition_To_v1beta1_CustomResourceColumnDefinition(in, out, s)
 }
 
+func autoConvert_v1beta1_CustomResourceConversion_To_apiextensions_CustomResourceConversion(in *CustomResourceConversion, out *apiextensions.CustomResourceConversion, s conversion.Scope) error {
+	out.Strategy = apiextensions.ConversionStrategyType(in.Strategy)
+	out.WebhookClientConfig = (*apiextensions.WebhookClientConfig)(unsafe.Pointer(in.WebhookClientConfig))
+	return nil
+}
+
+// Convert_v1beta1_CustomResourceConversion_To_apiextensions_CustomResourceConversion is an autogenerated conversion function.
+func Convert_v1beta1_CustomResourceConversion_To_apiextensions_CustomResourceConversion(in *CustomResourceConversion, out *apiextensions.CustomResourceConversion, s conversion.Scope) error {
+	return autoConvert_v1beta1_CustomResourceConversion_To_apiextensions_CustomResourceConversion(in, out, s)
+}
+
+func autoConvert_apiextensions_CustomResourceConversion_To_v1beta1_CustomResourceConversion(in *apiextensions.CustomResourceConversion, out *CustomResourceConversion, s conversion.Scope) error {
+	out.Strategy = ConversionStrategyType(in.Strategy)
+	out.WebhookClientConfig = (*WebhookClientConfig)(unsafe.Pointer(in.WebhookClientConfig))
+	return nil
+}
+
+// Convert_apiextensions_CustomResourceConversion_To_v1beta1_CustomResourceConversion is an autogenerated conversion function.
+func Convert_apiextensions_CustomResourceConversion_To_v1beta1_CustomResourceConversion(in *apiextensions.CustomResourceConversion, out *CustomResourceConversion, s conversion.Scope) error {
+	return autoConvert_apiextensions_CustomResourceConversion_To_v1beta1_CustomResourceConversion(in, out, s)
+}
+
 func autoConvert_v1beta1_CustomResourceDefinition_To_apiextensions_CustomResourceDefinition(in *CustomResourceDefinition, out *apiextensions.CustomResourceDefinition, s conversion.Scope) error {
 	out.ObjectMeta = in.ObjectMeta
 	if err := Convert_v1beta1_CustomResourceDefinitionSpec_To_apiextensions_CustomResourceDefinitionSpec(&in.Spec, &out.Spec, s); err != nil {
@@ -414,6 +466,7 @@ func autoConvert_v1beta1_CustomResourceDefinitionSpec_To_apiextensions_CustomRes
 	out.Subresources = (*apiextensions.CustomResourceSubresources)(unsafe.Pointer(in.Subresources))
 	out.Versions = *(*[]apiextensions.CustomResourceDefinitionVersion)(unsafe.Pointer(&in.Versions))
 	out.AdditionalPrinterColumns = *(*[]apiextensions.CustomResourceColumnDefinition)(unsafe.Pointer(&in.AdditionalPrinterColumns))
+	out.Conversion = (*apiextensions.CustomResourceConversion)(unsafe.Pointer(in.Conversion))
 	return nil
 }
 
@@ -441,6 +494,7 @@ func autoConvert_apiextensions_CustomResourceDefinitionSpec_To_v1beta1_CustomRes
 	out.Subresources = (*CustomResourceSubresources)(unsafe.Pointer(in.Subresources))
 	out.Versions = *(*[]CustomResourceDefinitionVersion)(unsafe.Pointer(&in.Versions))
 	out.AdditionalPrinterColumns = *(*[]CustomResourceColumnDefinition)(unsafe.Pointer(&in.AdditionalPrinterColumns))
+	out.Conversion = (*CustomResourceConversion)(unsafe.Pointer(in.Conversion))
 	return nil
 }
 
@@ -1123,3 +1177,51 @@ func autoConvert_apiextensions_JSONSchemaPropsOrStringArray_To_v1beta1_JSONSchem
 func Convert_apiextensions_JSONSchemaPropsOrStringArray_To_v1beta1_JSONSchemaPropsOrStringArray(in *apiextensions.JSONSchemaPropsOrStringArray, out *JSONSchemaPropsOrStringArray, s conversion.Scope) error {
 	return autoConvert_apiextensions_JSONSchemaPropsOrStringArray_To_v1beta1_JSONSchemaPropsOrStringArray(in, out, s)
 }
+
+func autoConvert_v1beta1_ServiceReference_To_apiextensions_ServiceReference(in *ServiceReference, out *apiextensions.ServiceReference, s conversion.Scope) error {
+	out.Namespace = in.Namespace
+	out.Name = in.Name
+	out.Path = (*string)(unsafe.Pointer(in.Path))
+	return nil
+}
+
+// Convert_v1beta1_ServiceReference_To_apiextensions_ServiceReference is an autogenerated conversion function.
+func Convert_v1beta1_ServiceReference_To_apiextensions_ServiceReference(in *ServiceReference, out *apiextensions.ServiceReference, s conversion.Scope) error {
+	return autoConvert_v1beta1_ServiceReference_To_apiextensions_ServiceReference(in, out, s)
+}
+
+func autoConvert_apiextensions_ServiceReference_To_v1beta1_ServiceReference(in *apiextensions.ServiceReference, out *ServiceReference, s conversion.Scope) error {
+	out.Namespace = in.Namespace
+	out.Name = in.Name
+	out.Path = (*string)(unsafe.Pointer(in.Path))
+	return nil
+}
+
+// Convert_apiextensions_ServiceReference_To_v1beta1_ServiceReference is an autogenerated conversion function.
+func Convert_apiextensions_ServiceReference_To_v1beta1_ServiceReference(in *apiextensions.ServiceReference, out *ServiceReference, s conversion.Scope) error {
+	return autoConvert_apiextensions_ServiceReference_To_v1beta1_ServiceReference(in, out, s)
+}
+
+func autoConvert_v1beta1_WebhookClientConfig_To_apiextensions_WebhookClientConfig(in *WebhookClientConfig, out *apiextensions.WebhookClientConfig, s conversion.Scope) error {
+	out.URL = (*string)(unsafe.Pointer(in.URL))
+	out.Service = (*apiextensions.ServiceReference)(unsafe.Pointer(in.Service))
+	out.CABundle = *(*[]byte)(unsafe.Pointer(&in.CABundle))
+	return nil
+}
+
+// Convert_v1beta1_WebhookClientConfig_To_apiextensions_WebhookClientConfig is an autogenerated conversion function.
+func Convert_v1beta1_WebhookClientConfig_To_apiextensions_WebhookClientConfig(in *WebhookClientConfig, out *apiextensions.WebhookClientConfig, s conversion.Scope) error {
+	return autoConvert_v1beta1_WebhookClientConfig_To_apiextensions_WebhookClientConfig(in, out, s)
+}
+
+func autoConvert_apiextensions_WebhookClientConfig_To_v1beta1_WebhookClientConfig(in *apiextensions.WebhookClientConfig, out *WebhookClientConfig, s conversion.Scope) error {
+	out.URL = (*string)(unsafe.Pointer(in.URL))
+	out.Service = (*ServiceReference)(unsafe.Pointer(in.Service))
+	out.CABundle = *(*[]byte)(unsafe.Pointer(&in.CABundle))
+	return nil
+}
+
+// Convert_apiextensions_WebhookClientConfig_To_v1beta1_WebhookClientConfig is an autogenerated conversion function.
+func Convert_apiextensions_WebhookClientConfig_To_v1beta1_WebhookClientConfig(in *apiextensions.WebhookClientConfig, out *WebhookClientConfig, s conversion.Scope) error {
+	return autoConvert_apiextensions_WebhookClientConfig_To_v1beta1_WebhookClientConfig(in, out, s)
+}

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/zz_generated.deepcopy.go

@@ -25,6 +25,88 @@ import (
 )
 
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ConversionRequest) DeepCopyInto(out *ConversionRequest) {
+	*out = *in
+	if in.Objects != nil {
+		in, out := &in.Objects, &out.Objects
+		*out = make([]runtime.RawExtension, len(*in))
+		for i := range *in {
+			(*in)[i].DeepCopyInto(&(*out)[i])
+		}
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ConversionRequest.
+func (in *ConversionRequest) DeepCopy() *ConversionRequest {
+	if in == nil {
+		return nil
+	}
+	out := new(ConversionRequest)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ConversionResponse) DeepCopyInto(out *ConversionResponse) {
+	*out = *in
+	if in.ConvertedObjects != nil {
+		in, out := &in.ConvertedObjects, &out.ConvertedObjects
+		*out = make([]runtime.RawExtension, len(*in))
+		for i := range *in {
+			(*in)[i].DeepCopyInto(&(*out)[i])
+		}
+	}
+	in.Result.DeepCopyInto(&out.Result)
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ConversionResponse.
+func (in *ConversionResponse) DeepCopy() *ConversionResponse {
+	if in == nil {
+		return nil
+	}
+	out := new(ConversionResponse)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ConversionReview) DeepCopyInto(out *ConversionReview) {
+	*out = *in
+	out.TypeMeta = in.TypeMeta
+	if in.Request != nil {
+		in, out := &in.Request, &out.Request
+		*out = new(ConversionRequest)
+		(*in).DeepCopyInto(*out)
+	}
+	if in.Response != nil {
+		in, out := &in.Response, &out.Response
+		*out = new(ConversionResponse)
+		(*in).DeepCopyInto(*out)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ConversionReview.
+func (in *ConversionReview) DeepCopy() *ConversionReview {
+	if in == nil {
+		return nil
+	}
+	out := new(ConversionReview)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyObject is an autogenerated deepcopy function, copying the receiver, creating a new runtime.Object.
+func (in *ConversionReview) DeepCopyObject() runtime.Object {
+	if c := in.DeepCopy(); c != nil {
+		return c
+	}
+	return nil
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *CustomResourceColumnDefinition) DeepCopyInto(out *CustomResourceColumnDefinition) {
 	*out = *in
 	return
@@ -41,6 +123,27 @@ func (in *CustomResourceColumnDefinition) DeepCopy() *CustomResourceColumnDefini
 }
 
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *CustomResourceConversion) DeepCopyInto(out *CustomResourceConversion) {
+	*out = *in
+	if in.WebhookClientConfig != nil {
+		in, out := &in.WebhookClientConfig, &out.WebhookClientConfig
+		*out = new(WebhookClientConfig)
+		(*in).DeepCopyInto(*out)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new CustomResourceConversion.
+func (in *CustomResourceConversion) DeepCopy() *CustomResourceConversion {
+	if in == nil {
+		return nil
+	}
+	out := new(CustomResourceConversion)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *CustomResourceDefinition) DeepCopyInto(out *CustomResourceDefinition) {
 	*out = *in
 	out.TypeMeta = in.TypeMeta
@@ -168,6 +271,11 @@ func (in *CustomResourceDefinitionSpec) DeepCopyInto(out *CustomResourceDefiniti
 		*out = make([]CustomResourceColumnDefinition, len(*in))
 		copy(*out, *in)
 	}
+	if in.Conversion != nil {
+		in, out := &in.Conversion, &out.Conversion
+		*out = new(CustomResourceConversion)
+		(*in).DeepCopyInto(*out)
+	}
 	return
 }
 
@@ -468,3 +576,55 @@ func (in *JSONSchemaPropsOrStringArray) DeepCopy() *JSONSchemaPropsOrStringArray
 	in.DeepCopyInto(out)
 	return out
 }
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ServiceReference) DeepCopyInto(out *ServiceReference) {
+	*out = *in
+	if in.Path != nil {
+		in, out := &in.Path, &out.Path
+		*out = new(string)
+		**out = **in
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ServiceReference.
+func (in *ServiceReference) DeepCopy() *ServiceReference {
+	if in == nil {
+		return nil
+	}
+	out := new(ServiceReference)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *WebhookClientConfig) DeepCopyInto(out *WebhookClientConfig) {
+	*out = *in
+	if in.URL != nil {
+		in, out := &in.URL, &out.URL
+		*out = new(string)
+		**out = **in
+	}
+	if in.Service != nil {
+		in, out := &in.Service, &out.Service
+		*out = new(ServiceReference)
+		(*in).DeepCopyInto(*out)
+	}
+	if in.CABundle != nil {
+		in, out := &in.CABundle, &out.CABundle
+		*out = make([]byte, len(*in))
+		copy(*out, *in)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new WebhookClientConfig.
+func (in *WebhookClientConfig) DeepCopy() *WebhookClientConfig {
+	if in == nil {
+		return nil
+	}
+	out := new(WebhookClientConfig)
+	in.DeepCopyInto(out)
+	return out
+}

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/BUILD

@@ -20,6 +20,7 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/util/validation:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/validation/field:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/feature:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/webhook:go_default_library",
     ],
 )
 

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go

@@ -18,6 +18,7 @@ package validation
 
 import (
 	"fmt"
+	"k8s.io/apiserver/pkg/util/webhook"
 	"reflect"
 	"strings"
 
@@ -110,13 +111,7 @@ func ValidateCustomResourceDefinitionSpec(spec *apiextensions.CustomResourceDefi
 		allErrs = append(allErrs, field.Invalid(fldPath.Child("group"), spec.Group, "should be a domain with at least one dot"))
 	}
 
-	switch spec.Scope {
-	case "":
-		allErrs = append(allErrs, field.Required(fldPath.Child("scope"), ""))
-	case apiextensions.ClusterScoped, apiextensions.NamespaceScoped:
-	default:
-		allErrs = append(allErrs, field.NotSupported(fldPath.Child("scope"), spec.Scope, []string{string(apiextensions.ClusterScoped), string(apiextensions.NamespaceScoped)}))
-	}
+	allErrs = append(allErrs, validateEnumStrings(fldPath.Child("scope"), string(spec.Scope), []string{string(apiextensions.ClusterScoped), string(apiextensions.NamespaceScoped)}, true)...)
 
 	storageFlagCount := 0
 	versionsMap := map[string]bool{}
@@ -187,6 +182,54 @@ func ValidateCustomResourceDefinitionSpec(spec *apiextensions.CustomResourceDefi
 		}
 	}
 
+	allErrs = append(allErrs, ValidateCustomResourceConversion(spec.Conversion, fldPath.Child("conversion"))...)
+
+	return allErrs
+}
+
+func validateEnumStrings(fldPath *field.Path, value string, accepted []string, required bool) field.ErrorList {
+	if value == "" {
+		if required {
+			return field.ErrorList{field.Required(fldPath, "")}
+		}
+		return field.ErrorList{}
+	}
+	for _, a := range accepted {
+		if a == value {
+			return field.ErrorList{}
+		}
+	}
+	return field.ErrorList{field.NotSupported(fldPath, value, accepted)}
+}
+
+// ValidateCustomResourceConversion statically validates
+func ValidateCustomResourceConversion(conversion *apiextensions.CustomResourceConversion, fldPath *field.Path) field.ErrorList {
+	allErrs := field.ErrorList{}
+	if conversion == nil {
+		return allErrs
+	}
+	allErrs = append(allErrs, validateEnumStrings(fldPath.Child("strategy"), string(conversion.Strategy), []string{string(apiextensions.NoneConverter), string(apiextensions.WebhookConverter)}, true)...)
+	if conversion.Strategy == apiextensions.WebhookConverter {
+		if conversion.WebhookClientConfig == nil {
+			if utilfeature.DefaultFeatureGate.Enabled(apiextensionsfeatures.CustomResourceWebhookConversion) {
+				allErrs = append(allErrs, field.Required(fldPath.Child("webhookClientConfig"), "required when strategy is set to Webhook"))
+			} else {
+				allErrs = append(allErrs, field.Required(fldPath.Child("webhookClientConfig"), "required when strategy is set to Webhook, but not allowed because the CustomResourceWebhookConversion feature is disabled"))
+			}
+		} else {
+			cc := conversion.WebhookClientConfig
+			switch {
+			case (cc.URL == nil) == (cc.Service == nil):
+				allErrs = append(allErrs, field.Required(fldPath.Child("webhookClientConfig"), "exactly one of url or service is required"))
+			case cc.URL != nil:
+				allErrs = append(allErrs, webhook.ValidateWebhookURL(fldPath.Child("webhookClientConfig").Child("url"), *cc.URL, true)...)
+			case cc.Service != nil:
+				allErrs = append(allErrs, webhook.ValidateWebhookService(fldPath.Child("webhookClientConfig").Child("service"), cc.Service.Name, cc.Service.Namespace, cc.Service.Path)...)
+			}
+		}
+	} else if conversion.WebhookClientConfig != nil {
+		allErrs = append(allErrs, field.Forbidden(fldPath.Child("webhookClientConfig"), "should not be set when strategy is not set to Webhook"))
+	}
 	return allErrs
 }
 

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go

@@ -49,6 +49,8 @@ func (v validationMatch) matches(err *field.Error) bool {
 	return err.Type == v.errorType && err.Field == v.path.String()
 }
 
+func strPtr(s string) *string { return &s }
+
 func TestValidateCustomResourceDefinition(t *testing.T) {
 	singleVersionList := []apiextensions.CustomResourceDefinitionVersion{
 		{
@@ -63,6 +65,205 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 		errors   []validationMatch
 	}{
 		{
+			name: "webhookconfig: blank URL",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group: "group.com",
+					Scope: apiextensions.ResourceScope("Cluster"),
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							Name:    "version",
+							Served:  true,
+							Storage: true,
+						},
+						{
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+						},
+					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("Webhook"),
+						WebhookClientConfig: &apiextensions.WebhookClientConfig{
+							URL: strPtr("https://example.com/webhook"),
+							Service: &apiextensions.ServiceReference{
+								Name:      "n",
+								Namespace: "ns",
+							},
+						},
+					},
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version"},
+				},
+			},
+			errors: []validationMatch{
+				required("spec", "conversion", "webhookClientConfig"),
+			},
+		},
+		{
+			name: "webhookconfig: both service and URL provided",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group: "group.com",
+					Scope: apiextensions.ResourceScope("Cluster"),
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							Name:    "version",
+							Served:  true,
+							Storage: true,
+						},
+						{
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+						},
+					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("Webhook"),
+						WebhookClientConfig: &apiextensions.WebhookClientConfig{
+							URL: strPtr(""),
+						},
+					},
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version"},
+				},
+			},
+			errors: []validationMatch{
+				invalid("spec", "conversion", "webhookClientConfig", "url"),
+				invalid("spec", "conversion", "webhookClientConfig", "url"),
+			},
+		},
+		{
+			name: "webhookconfig_should_not_be_set",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group: "group.com",
+					Scope: apiextensions.ResourceScope("Cluster"),
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							Name:    "version",
+							Served:  true,
+							Storage: true,
+						},
+						{
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+						},
+					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+						WebhookClientConfig: &apiextensions.WebhookClientConfig{
+							URL: strPtr("https://example.com/webhook"),
+						},
+					},
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version"},
+				},
+			},
+			errors: []validationMatch{
+				forbidden("spec", "conversion", "webhookClientConfig"),
+			},
+		},
+		{
+			name: "missing_webhookconfig",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group: "group.com",
+					Scope: apiextensions.ResourceScope("Cluster"),
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							Name:    "version",
+							Served:  true,
+							Storage: true,
+						},
+						{
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+						},
+					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("Webhook"),
+					},
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version"},
+				},
+			},
+			errors: []validationMatch{
+				required("spec", "conversion", "webhookClientConfig"),
+			},
+		},
+		{
+			name: "invalid_conversion_strategy",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group: "group.com",
+					Scope: apiextensions.ResourceScope("Cluster"),
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							Name:    "version",
+							Served:  true,
+							Storage: true,
+						},
+						{
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+						},
+					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("non_existing_conversion"),
+					},
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version"},
+				},
+			},
+			errors: []validationMatch{
+				unsupported("spec", "conversion", "strategy"),
+			},
+		},
+		{
 			name: "no_storage_version",
 			resource: &apiextensions.CustomResourceDefinition{
 				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
@@ -87,6 +288,9 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 							Storage: false,
 						},
 					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
 				},
 				Status: apiextensions.CustomResourceDefinitionStatus{
 					StoredVersions: []string{"version"},
@@ -121,6 +325,9 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 							Storage: true,
 						},
 					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
 				},
 				Status: apiextensions.CustomResourceDefinitionStatus{
 					StoredVersions: []string{"version"},
@@ -156,6 +363,9 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 							Storage: true,
 						},
 					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
 				},
 				Status: apiextensions.CustomResourceDefinitionStatus{
 					StoredVersions: []string{"version"},
@@ -185,6 +395,9 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 							Storage: true,
 						},
 					},
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
 				},
 				Status: apiextensions.CustomResourceDefinitionStatus{
 					StoredVersions: []string{},
@@ -283,6 +496,9 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 					Group:    "group.c(*&om",
 					Version:  "version",
 					Versions: singleVersionList,
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
 					Names: apiextensions.CustomResourceDefinitionNames{
 						Plural:   "plural",
 						Singular: "singular",
@@ -316,7 +532,10 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 					Group:    "group.com",
 					Version:  "version",
 					Versions: singleVersionList,
-					Scope:    apiextensions.NamespaceScoped,
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
+					Scope: apiextensions.NamespaceScoped,
 					Names: apiextensions.CustomResourceDefinitionNames{
 						Plural:   "plural",
 						Singular: "singular",
@@ -348,7 +567,10 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 					Group:    "group.com",
 					Version:  "version",
 					Versions: singleVersionList,
-					Scope:    apiextensions.NamespaceScoped,
+					Conversion: &apiextensions.CustomResourceConversion{
+						Strategy: apiextensions.ConversionStrategyType("None"),
+					},
+					Scope: apiextensions.NamespaceScoped,
 					Names: apiextensions.CustomResourceDefinitionNames{
 						Plural:   "plural",
 						Singular: "singular",

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/zz_generated.deepcopy.go

@@ -41,6 +41,27 @@ func (in *CustomResourceColumnDefinition) DeepCopy() *CustomResourceColumnDefini
 }
 
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *CustomResourceConversion) DeepCopyInto(out *CustomResourceConversion) {
+	*out = *in
+	if in.WebhookClientConfig != nil {
+		in, out := &in.WebhookClientConfig, &out.WebhookClientConfig
+		*out = new(WebhookClientConfig)
+		(*in).DeepCopyInto(*out)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new CustomResourceConversion.
+func (in *CustomResourceConversion) DeepCopy() *CustomResourceConversion {
+	if in == nil {
+		return nil
+	}
+	out := new(CustomResourceConversion)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *CustomResourceDefinition) DeepCopyInto(out *CustomResourceDefinition) {
 	*out = *in
 	out.TypeMeta = in.TypeMeta
@@ -168,6 +189,11 @@ func (in *CustomResourceDefinitionSpec) DeepCopyInto(out *CustomResourceDefiniti
 		*out = make([]CustomResourceColumnDefinition, len(*in))
 		copy(*out, *in)
 	}
+	if in.Conversion != nil {
+		in, out := &in.Conversion, &out.Conversion
+		*out = new(CustomResourceConversion)
+		(*in).DeepCopyInto(*out)
+	}
 	return
 }
 
@@ -447,3 +473,55 @@ func (in *JSONSchemaPropsOrStringArray) DeepCopy() *JSONSchemaPropsOrStringArray
 	in.DeepCopyInto(out)
 	return out
 }
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ServiceReference) DeepCopyInto(out *ServiceReference) {
+	*out = *in
+	if in.Path != nil {
+		in, out := &in.Path, &out.Path
+		*out = new(string)
+		**out = **in
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ServiceReference.
+func (in *ServiceReference) DeepCopy() *ServiceReference {
+	if in == nil {
+		return nil
+	}
+	out := new(ServiceReference)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *WebhookClientConfig) DeepCopyInto(out *WebhookClientConfig) {
+	*out = *in
+	if in.URL != nil {
+		in, out := &in.URL, &out.URL
+		*out = new(string)
+		**out = **in
+	}
+	if in.Service != nil {
+		in, out := &in.Service, &out.Service
+		*out = new(ServiceReference)
+		(*in).DeepCopyInto(*out)
+	}
+	if in.CABundle != nil {
+		in, out := &in.CABundle, &out.CABundle
+		*out = make([]byte, len(*in))
+		copy(*out, *in)
+	}
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new WebhookClientConfig.
+func (in *WebhookClientConfig) DeepCopy() *WebhookClientConfig {
+	if in == nil {
+		return nil
+	}
+	out := new(WebhookClientConfig)
+	in.DeepCopyInto(out)
+	return out
+}

staging/src/k8s.io/apiextensions-apiserver/pkg/features/kube_features.go

@@ -40,6 +40,12 @@ const (
 	//
 	// CustomResourceSubresources defines the subresources for CustomResources
 	CustomResourceSubresources utilfeature.Feature = "CustomResourceSubresources"
+
+	// owner: @mbohlool
+	// alpha: v1.13
+	//
+	// CustomResourceWebhookConversion defines the webhook conversion for Custom Resources.
+	CustomResourceWebhookConversion utilfeature.Feature = "CustomResourceWebhookConversion"
 )
 
 func init() {
@@ -50,6 +56,7 @@ func init() {
 // To add a new feature, define a key for it above and add it here. The features will be
 // available throughout Kubernetes binaries.
 var defaultKubernetesFeatureGates = map[utilfeature.Feature]utilfeature.FeatureSpec{
-	CustomResourceValidation:   {Default: true, PreRelease: utilfeature.Beta},
-	CustomResourceSubresources: {Default: true, PreRelease: utilfeature.Beta},
+	CustomResourceValidation:        {Default: true, PreRelease: utilfeature.Beta},
+	CustomResourceSubresources:      {Default: true, PreRelease: utilfeature.Beta},
+	CustomResourceWebhookConversion: {Default: false, PreRelease: utilfeature.Alpha},
 }

staging/src/k8s.io/apiextensions-apiserver/pkg/registry/customresourcedefinition/strategy.go

@@ -20,6 +20,9 @@ import (
 	"context"
 	"fmt"
 
+	"k8s.io/apiextensions-apiserver/pkg/apis/apiextensions"
+	"k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation"
+	apiextensionsfeatures "k8s.io/apiextensions-apiserver/pkg/features"
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/labels"
@@ -29,10 +32,6 @@ import (
 	"k8s.io/apiserver/pkg/storage"
 	"k8s.io/apiserver/pkg/storage/names"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
-
-	"k8s.io/apiextensions-apiserver/pkg/apis/apiextensions"
-	"k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation"
-	apiextensionsfeatures "k8s.io/apiextensions-apiserver/pkg/features"
 )
 
 // strategy implements behavior for CustomResources.
@@ -62,6 +61,9 @@ func (strategy) PrepareForCreate(ctx context.Context, obj runtime.Object) {
 	if !utilfeature.DefaultFeatureGate.Enabled(apiextensionsfeatures.CustomResourceSubresources) {
 		crd.Spec.Subresources = nil
 	}
+	if !utilfeature.DefaultFeatureGate.Enabled(apiextensionsfeatures.CustomResourceWebhookConversion) && crd.Spec.Conversion != nil {
+		crd.Spec.Conversion.WebhookClientConfig = nil
+	}
 
 	for _, v := range crd.Spec.Versions {
 		if v.Storage {
@@ -99,6 +101,11 @@ func (strategy) PrepareForUpdate(ctx context.Context, obj, old runtime.Object) {
 		newCRD.Spec.Subresources = nil
 		oldCRD.Spec.Subresources = nil
 	}
+	if !utilfeature.DefaultFeatureGate.Enabled(apiextensionsfeatures.CustomResourceWebhookConversion) && newCRD.Spec.Conversion != nil {
+		if oldCRD.Spec.Conversion == nil || newCRD.Spec.Conversion.WebhookClientConfig == nil {
+			newCRD.Spec.Conversion.WebhookClientConfig = nil
+		}
+	}
 
 	for _, v := range newCRD.Spec.Versions {
 		if v.Storage {

staging/src/k8s.io/apiserver/pkg/util/webhook/BUILD

@@ -13,6 +13,7 @@ go_library(
         "client.go",
         "error.go",
         "serviceresolver.go",
+        "validation.go",
         "webhook.go",
     ],
     importmap = "k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/util/webhook",
@@ -24,6 +25,8 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/runtime/serializer:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/errors:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/net:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/util/validation:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/util/validation/field:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//staging/src/k8s.io/client-go/rest:go_default_library",
         "//staging/src/k8s.io/client-go/tools/clientcmd:go_default_library",

staging/src/k8s.io/apiserver/pkg/util/webhook/validation.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 webhook
+
+import (
+	"fmt"
+	"net/url"
+	"strings"
+
+	"k8s.io/apimachinery/pkg/util/validation"
+	"k8s.io/apimachinery/pkg/util/validation/field"
+)
+
+// ValidateWebhookURL validates webhook's URL.
+func ValidateWebhookURL(fldPath *field.Path, URL string, forceHttps bool) field.ErrorList {
+	var allErrors field.ErrorList
+	const form = "; desired format: https://host[/path]"
+	if u, err := url.Parse(URL); err != nil {
+		allErrors = append(allErrors, field.Required(fldPath, "url must be a valid URL: "+err.Error()+form))
+	} else {
+		if forceHttps && u.Scheme != "https" {
+			allErrors = append(allErrors, field.Invalid(fldPath, u.Scheme, "'https' is the only allowed URL scheme"+form))
+		}
+		if len(u.Host) == 0 {
+			allErrors = append(allErrors, field.Invalid(fldPath, u.Host, "host must be provided"+form))
+		}
+		if u.User != nil {
+			allErrors = append(allErrors, field.Invalid(fldPath, u.User.String(), "user information is not permitted in the URL"))
+		}
+		if len(u.Fragment) != 0 {
+			allErrors = append(allErrors, field.Invalid(fldPath, u.Fragment, "fragments are not permitted in the URL"))
+		}
+		if len(u.RawQuery) != 0 {
+			allErrors = append(allErrors, field.Invalid(fldPath, u.RawQuery, "query parameters are not permitted in the URL"))
+		}
+	}
+	return allErrors
+}
+
+func ValidateWebhookService(fldPath *field.Path, namespace, name string, path *string) field.ErrorList {
+	var allErrors field.ErrorList
+
+	if len(name) == 0 {
+		allErrors = append(allErrors, field.Required(fldPath.Child("name"), "service name is required"))
+	}
+
+	if len(namespace) == 0 {
+		allErrors = append(allErrors, field.Required(fldPath.Child("namespace"), "service namespace is required"))
+	}
+
+	if path == nil {
+		return allErrors
+	}
+
+	// TODO: replace below with url.Parse + verifying that host is empty?
+
+	urlPath := *path
+	if urlPath == "/" || len(urlPath) == 0 {
+		return allErrors
+	}
+	if urlPath == "//" {
+		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "segment[0] may not be empty"))
+		return allErrors
+	}
+
+	if !strings.HasPrefix(urlPath, "/") {
+		allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, "must start with a '/'"))
+	}
+
+	urlPathToCheck := urlPath[1:]
+	if strings.HasSuffix(urlPathToCheck, "/") {
+		urlPathToCheck = urlPathToCheck[:len(urlPathToCheck)-1]
+	}
+	steps := strings.Split(urlPathToCheck, "/")
+	for i, step := range steps {
+		if len(step) == 0 {
+			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d] may not be empty", i)))
+			continue
+		}
+		failures := validation.IsDNS1123Subdomain(step)
+		for _, failure := range failures {
+			allErrors = append(allErrors, field.Invalid(fldPath.Child("path"), urlPath, fmt.Sprintf("segment[%d]: %v", i, failure)))
+		}
+	}
+
+	return allErrors
+}