(kustomize/v2, go/v4): Add Hub and Spoke for conversion webhooks

This PR introduces the initial implementation of the hub-and-spoke model for handling conversion webhooks. The goal is to streamline the conversion process by utilizing a central hub to speak a specific version of the same Group and Kind.

- **Single Spoke Support (A to B, Same Kind and Group):**
  The system will allow only one spoke version for conversions (i.e., converting from Version A to Version B within the same kind and group).

- **Future Expansion (List of GKV Spokes):**
  In the future, based on user feedback or demand, we can expand to support a list of **GKV spokes**, allowing for greater flexibility in conversions across different versions, kinds, and groups.

- **Advanced Case Handling (Manual Steps):**
  For more advanced cases, users can proceed without specifying a spoke. In this scenario, the conversion process will still occur without the spoke, enabling users to continue. However, they will be required to complete specific advanced steps manually.

Closes; kubernetes-sigs#2589

docs/book/src/multiversion-tutorial/testdata/project/PROJECT

@@ -20,9 +20,7 @@ resources:
   webhooks:
     conversion: true
     defaulting: true
-    spoke:
-    - v2
-    - v2
+    spoke: v2
     validation: true
     webhookVersion: v1
 - api:

pkg/cli/alpha/internal/generate.go

@@ -369,8 +369,8 @@ func getWebhookResourceFlags(resource resource.Resource) []string {
 	}
 	if resource.HasConversionWebhook() {
 		args = append(args, "--conversion")
-		for _, spoke := range resource.Webhooks.Spoke {
-			args = append(args, "--spoke", spoke)
+		if resource.Webhooks.Spoke != "" {
+			args = append(args, "--spoke", resource.Webhooks.Spoke)
 		}
 	}
 	return args

pkg/model/resource/webhooks.go

@@ -34,7 +34,7 @@ type Webhooks struct {
 	// Conversion specifies if a conversion webhook is associated to the resource.
 	Conversion bool `json:"conversion,omitempty"`
 
-	Spoke []string `json:"spoke,omitempty"`
+	Spoke string `json:"spoke,omitempty"`
 }
 
 // Validate checks that the Webhooks is valid.
@@ -80,7 +80,7 @@ func (webhooks *Webhooks) Update(other *Webhooks) error {
 	webhooks.Conversion = webhooks.Conversion || other.Conversion
 
 	// Update Spoke.
-	webhooks.Spoke = append(webhooks.Spoke, other.Spoke...)
+	webhooks.Spoke = other.Spoke
 
 	return nil
 }
@@ -89,23 +89,3 @@ func (webhooks *Webhooks) Update(other *Webhooks) error {
 func (webhooks Webhooks) IsEmpty() bool {
 	return webhooks.WebhookVersion == "" && !webhooks.Defaulting && !webhooks.Validation && !webhooks.Conversion
 }
-
-// HasSpokeVersion returns true if the spoke version is present in the list of spoke versions.
-func (webhooks Webhooks) HasSpokeVersion(version string) bool {
-	for _, v := range webhooks.Spoke {
-		if v == version {
-			return true
-		}
-	}
-	return false
-}
-
-// HasAnySpokeVersionFrom returns true if any spoke versions are present in the list of spoke versions.
-func (webhooks Webhooks) HasAnySpokeVersionFrom(values []string) bool {
-	for _, v := range values {
-		if webhooks.HasSpokeVersion(v) {
-			return true
-		}
-	}
-	return false
-}

pkg/model/resource/webhooks_test.go

@@ -52,14 +52,14 @@ var _ = Describe("Webhooks", func() {
 				Defaulting:     true,
 				Validation:     true,
 				Conversion:     true,
-				Spoke:          []string{"v2"},
+				Spoke:          "v2",
 			}
 			Expect(webhook.Update(nil)).To(Succeed())
 			Expect(webhook.WebhookVersion).To(Equal(v1))
 			Expect(webhook.Defaulting).To(BeTrue())
 			Expect(webhook.Validation).To(BeTrue())
 			Expect(webhook.Conversion).To(BeTrue())
-			Expect(webhook.Spoke).To(Equal([]string{"v2"}))
+			Expect(webhook.Spoke).To(Equal("v2"))
 		})
 
 		Context("webhooks version", func() {

pkg/plugins/golang/options.go

@@ -74,7 +74,7 @@ type Options struct {
 	DoConversion bool
 
 	// Spoke version for conversion webhook
-	Spoke []string
+	Spoke string
 }
 
 // UpdateResource updates the provided resource with the options

pkg/plugins/golang/v4/scaffolds/internal/templates/api/spoke.go

@@ -32,17 +32,16 @@ type Spoke struct {
 	machinery.BoilerplateMixin
 	machinery.ResourceMixin
 
-	Force        bool
-	SpokeVersion string
+	Force bool
 }
 
 // SetTemplateDefaults implements file.Template
 func (f *Spoke) SetTemplateDefaults() error {
 	if f.Path == "" {
 		if f.MultiGroup && f.Resource.Group != "" {
-			f.Path = filepath.Join("api", "%[group]", f.SpokeVersion, "%[kind]_conversion.go")
+			f.Path = filepath.Join("api", "%[group]", f.Resource.Webhooks.Spoke, "%[kind]_conversion.go")
 		} else {
-			f.Path = filepath.Join("api", f.SpokeVersion, "%[kind]_conversion.go")
+			f.Path = filepath.Join("api", f.Resource.Webhooks.Spoke, "%[kind]_conversion.go")
 		}
 	}
 
@@ -63,7 +62,7 @@ func (f *Spoke) SetTemplateDefaults() error {
 // nolint:lll
 const spokeTemplate = `{{ .Boilerplate }}
 
-package {{ .SpokeVersion }}
+package {{ .Resource.Webhooks.Spoke }}
 
 import (
 	"log"
@@ -78,18 +77,18 @@ func (src *{{ .Resource.Kind }}) ConvertTo(dstRaw conversion.Hub) error {
 	log.Printf("ConvertTo: converts this {{ .Resource.Kind }} to the Hub version ({{ .Resource.Version }});" +
 	"source: %s/%s and target: %s/%s", src.Namespace, src.Name, dst.Namespace, dst.Name)
 
-	// TODO(user): Implement conversion logic from {{ .SpokeVersion }} to {{ .Resource.Version }}
+	// TODO(user): Implement conversion logic from {{ .Resource.Webhooks.Spoke }} to {{ .Resource.Version }}
 	
     return nil
 }
 
-// ConvertFrom converts the Hub version ({{ .Resource.Version }}) to this {{ .Resource.Kind }} ({{ .SpokeVersion}}).
+// ConvertFrom converts the Hub version ({{ .Resource.Version }}) to this {{ .Resource.Kind }} ({{ .Resource.Webhooks.Spoke }}).
 func (dst *{{ .Resource.Kind }}) ConvertFrom(srcRaw conversion.Hub) error {
     src := srcRaw.(*{{ .Resource.ImportAlias }}.{{ .Resource.Kind }})
-    log.Printf("ConvertFrom: converts the Hub version ({{ .Resource.Version }}) to this {{ .Resource.Kind }} ({{ .SpokeVersion}});" +
+    log.Printf("ConvertFrom: converts the Hub version ({{ .Resource.Version }}) to this {{ .Resource.Kind }} ({{ .Resource.Webhooks.Spoke }});" +
 	"source: %s/%s and target: %s/%s", src.Namespace, src.Name, dst.Namespace, dst.Name)
 
-	// TODO(user): Implement conversion logic from {{ .Resource.Version }} to {{ .SpokeVersion }}
+	// TODO(user): Implement conversion logic from {{ .Resource.Version }} to {{ .Resource.Webhooks.Spoke }}
     
 	return nil
 }

pkg/plugins/golang/v4/scaffolds/webhook.go

@@ -124,18 +124,10 @@ func (s *webhookScaffolder) Scaffold() error {
 
 		if err := scaffold.Execute(
 			&api.Hub{Force: s.force},
+			&api.Spoke{Force: s.force},
 		); err != nil {
 			return err
 		}
-
-		// Create the spoke version conversion file for each spoke version
-		for _, spokeVersion := range s.resource.Webhooks.Spoke {
-			if err := scaffold.Execute(
-				&api.Spoke{Force: s.force, SpokeVersion: spokeVersion},
-			); err != nil {
-				return err
-			}
-		}
 		log.Println(`Webhook server has been set up for you.
 You need to implement the conversion.Hub and conversion.Convertible interfaces for your CRD types.`)
 	}

pkg/plugins/golang/v4/webhook.go

@@ -66,7 +66,7 @@ validating and/or conversion webhooks.
 
   # Create conversion webhook for Group: ship, Version: v1beta1
   # and Kind: Frigate
-  %[1]s create webhook --group ship --version v1beta1 --kind Frigate --conversion --spoke v1,v2,v3
+  %[1]s create webhook --group ship --version v1beta1 --kind Frigate --conversion --spoke v1
 `, cliMeta.CommandName)
 }
 
@@ -84,9 +84,9 @@ func (p *createWebhookSubcommand) BindFlags(fs *pflag.FlagSet) {
 	fs.BoolVar(&p.options.DoConversion, "conversion", false,
 		"if set, scaffold the conversion webhook")
 
-	fs.StringSliceVar(&p.options.Spoke, "spoke",
-		[]string{},
-		"comma-separated list of spoke versions for conversion webhook (i.e. --spoke v1,v2,v3)")
+	fs.StringVar(&p.options.Spoke, "spoke",
+		"",
+		"if set, scaffold the spoke implementation (i.e. --spoke v1,v2,v3)")
 
 	// TODO: remove for go/v5
 	fs.BoolVar(&p.isLegacyPath, "legacy", false,
@@ -149,21 +149,12 @@ func (p *createWebhookSubcommand) InjectResource(res *resource.Resource) error {
 	}
 
 	if p.options.DoConversion {
-		if res.HasConversionWebhook() &&
-			len(p.options.Spoke) > 0 &&
-			res.Webhooks.HasAnySpokeVersionFrom(p.options.Spoke) {
-			return fmt.Errorf("conversion webhook already exists with one or more spoke versions informed")
-		}
-
-		// Check if all spoke versions informed are api versions which exist in the resource
-		for _, spokeVersion := range p.options.Spoke {
-			spokeGKV := res.GVK
-			spokeGKV.Version = spokeVersion
-			_, err := p.config.GetResource(spokeGKV)
-			if err != nil {
-				return fmt.Errorf("resource does not have a version %s",
-					spokeVersion)
-			}
+		spokeGKV := res.GVK
+		spokeGKV.Version = p.options.Spoke
+		_, err := p.config.GetResource(spokeGKV)
+		if err != nil {
+			return fmt.Errorf("resource does not have a version %s",
+				p.options.Spoke)
 		}
 	}
 	return nil

test/e2e/v4/generate_test.go

@@ -421,12 +421,12 @@ func scaffoldConversionWebhook(kbc *utils.TestContext) {
 
 	err = pluginutil.ReplaceInFile(filepath.Join(kbc.Dir, "api/v2/conversiontest_conversion.go"),
 		"// TODO(user): Implement conversion logic from v1 to v2",
-		`dst.Spec.Size = src.Spec.Replicas`)
+		`src.Spec.Size = dst.Spec.Replicas`)
 	Expect(err).NotTo(HaveOccurred(), "failed to implement conversion logic from v1 to v2")
 
 	err = pluginutil.ReplaceInFile(filepath.Join(kbc.Dir, "api/v2/conversiontest_conversion.go"),
 		"// TODO(user): Implement conversion logic from v2 to v1",
-		`dst.Spec.Replicas = src.Spec.Size`)
+		`src.Spec.Replicas = dst.Spec.Size`)
 	Expect(err).NotTo(HaveOccurred(), "failed to implement conversion logic from v2 to v1")
 }
 

testdata/project-v4-multigroup/PROJECT

@@ -183,9 +183,7 @@ resources:
   version: v1
   webhooks:
     conversion: true
-    spoke:
-    - v2
-    - v2
+    spoke: v2
     webhookVersion: v1
 - api:
     crdVersion: v1

testdata/project-v4-with-plugins/PROJECT

@@ -60,9 +60,7 @@ resources:
   version: v1
   webhooks:
     conversion: true
-    spoke:
-    - v2
-    - v2
+    spoke: v2
     webhookVersion: v1
 - api:
     crdVersion: v1

testdata/project-v4/PROJECT

@@ -32,9 +32,7 @@ resources:
   version: v1
   webhooks:
     conversion: true
-    spoke:
-    - v2
-    - v2
+    spoke: v2
     webhookVersion: v1
 - api:
     crdVersion: v1