Admission webhook

cmd/main.go

@@ -210,6 +210,11 @@ func main() {
 			setupLog.Error(err, "unable to create controller", "controller", "K0sController")
 			os.Exit(1)
 		}
+
+		if err = (&controlplane.K0sControlPlaneValidator{}).SetupK0sControlPlaneWebhookWithManager(mgr); err != nil {
+			setupLog.Error(err, "unable to create validation webhook", "webhook", "K0sControlPlaneValidator")
+			os.Exit(1)
+		}
 	}
 
 	if isControllerEnabled(infrastructureController) {

config/webhook/manifests.yaml

@@ -0,0 +1,26 @@
+---
+apiVersion: admissionregistration.k8s.io/v1
+kind: ValidatingWebhookConfiguration
+metadata:
+  name: validating-webhook-configuration
+webhooks:
+- admissionReviewVersions:
+  - v1
+  clientConfig:
+    service:
+      name: webhook-service
+      namespace: system
+      path: /validate-v1beta1-k0scontrolplane
+  failurePolicy: Fail
+  name: validate-k0scontolplane-v1beta1.k0smotron.io
+  rules:
+  - apiGroups:
+    - controlplane.cluster.x-k8s.io
+    apiVersions:
+    - v1beta1
+    operations:
+    - CREATE
+    - UPDATE
+    resources:
+    - k0scontolplanes
+  sideEffects: None

internal/controller/controlplane/k0s_controlplane_webhook.go

@@ -0,0 +1,110 @@
+/*
+Copyright 2023.
+
+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 controlplane
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/k0sproject/version"
+	"k8s.io/apimachinery/pkg/runtime"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/webhook"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
+
+	"github.com/k0sproject/k0smotron/api/controlplane/v1beta1"
+)
+
+// +kubebuilder:webhook:path=/validate-v1beta1-k0scontrolplane,mutating=false,failurePolicy=fail,sideEffects=None,groups=controlplane.cluster.x-k8s.io,resources=k0scontolplanes,verbs=create;update,versions=v1beta1,name=validate-k0scontolplane-v1beta1.k0smotron.io,admissionReviewVersions=v1
+
+// K0sControlPlaneValidator struct is responsible for validating the K0sControlPlane resource when it is created, updated, or deleted.
+//
+// NOTE: The +kubebuilder:object:generate=false marker prevents controller-gen from generating DeepCopy methods,
+// as this struct is used only for temporary operations and does not need to be deeply copied.
+type K0sControlPlaneValidator struct {
+	//TODO(user): Add more fields as needed for validation
+}
+
+var _ webhook.CustomValidator = &K0sControlPlaneValidator{}
+
+// ValidateCreate implements webhook.CustomValidator so a webhook will be registered for the type K0sControlPlane.
+func (v *K0sControlPlaneValidator) ValidateCreate(ctx context.Context, obj runtime.Object) (admission.Warnings, error) {
+	kcp, ok := obj.(*v1beta1.K0sControlPlane)
+	if !ok {
+		return nil, fmt.Errorf("expected a K0sControlPlane object but got %T", obj)
+	}
+
+	return nil, validateK0sControlPlane(kcp)
+}
+
+// ValidateUpdate implements webhook.CustomValidator so a webhook will be registered for the type K0sControlPlane.
+func (v *K0sControlPlaneValidator) ValidateUpdate(ctx context.Context, oldObj, newObj runtime.Object) (admission.Warnings, error) {
+	newKCP, ok := newObj.(*v1beta1.K0sControlPlane)
+	if !ok {
+		return nil, fmt.Errorf("expected a new K0sControlPlane object but got %T", newObj)
+	}
+	oldKCP, ok := oldObj.(*v1beta1.K0sControlPlane)
+	if !ok {
+		return nil, fmt.Errorf("expected a old K0sControlPlane object but got %T", oldObj)
+	}
+
+	if oldKCP.Spec.Version != newKCP.Spec.Version {
+		oldV, err := version.NewVersion(oldKCP.Spec.Version)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse old version: %v", err)
+		}
+		newV, err := version.NewVersion(newKCP.Spec.Version)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse new version: %v", err)
+		}
+
+		// According to the Kubernetes skew policy, we can't upgrade more than one minor version at a time.
+		if newV.Core().Segments()[1]-oldV.Core().Segments()[1] > 1 {
+			return nil, fmt.Errorf("upgrading more than one minor version at a time is not allowed by the Kubernetes skew policy")
+		}
+	}
+
+	return nil, validateK0sControlPlane(newKCP)
+}
+
+// ValidateDelete implements webhook.CustomValidator so a webhook will be registered for the type K0sControlPlane.
+func (v *K0sControlPlaneValidator) ValidateDelete(ctx context.Context, obj runtime.Object) (admission.Warnings, error) {
+	return nil, nil
+}
+
+func validateK0sControlPlane(kcp *v1beta1.K0sControlPlane) error {
+	if kcp.Spec.UpdateStrategy == v1beta1.UpdateRecreate {
+
+		// If the cluster is running in single mode, we can't use the Recreate strategy
+		if kcp.Spec.K0sConfigSpec.Args != nil {
+			for _, arg := range kcp.Spec.K0sConfigSpec.Args {
+				if arg == "--single" {
+					return fmt.Errorf("UpdateStrategy Recreate strategy is not allowed when the cluster is running in single mode")
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+// SetupK0sControlPlaneWebhookWithManager registers the webhook for K0sControlPlane in the manager.
+func (v *K0sControlPlaneValidator) SetupK0sControlPlaneWebhookWithManager(mgr ctrl.Manager) error {
+	return ctrl.NewWebhookManagedBy(mgr).For(&v1beta1.K0sControlPlane{}).
+		WithValidator(&K0sControlPlaneValidator{}).
+		Complete()
+}