replace: eliminate conflict during cleanup of PVC finalizers (#350)

Operator updated PVC which is subject for removal, so this is expected
that update may conflict.
To avoid conflicts instead updating whole resource, patch is used.

Fixes #350

pkg/controllers/cluster/actions/replace.go

@@ -14,6 +14,7 @@ import (
 	"github.com/scylladb/scylla-operator/pkg/naming"
 	corev1 "k8s.io/api/core/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
@@ -184,12 +185,14 @@ func (a *RackReplaceNode) replaceNode(ctx context.Context, state *State, member
 			return false, errors.Wrap(err, "failed to get pvc")
 		}
 
-		// Remove finalizer, which will wait until pod is deleted.
-		// We want to delete pod anyway, so it's better to delete pvc immediately.
-		pvcCopy := p.DeepCopy()
-		pvcCopy.SetFinalizers([]string{})
-		if err := cc.Update(ctx, pvcCopy); err != nil {
-			return false, errors.Wrap(err, "failed to update pvc")
+		if len(p.Finalizers) != 0 {
+			// Remove finalizer, which will wait until pod is deleted.
+			// We want to delete pod anyway, so it's better to delete pvc immediately.
+			if err := cc.Patch(ctx, pvc, util.StrategicMergePatchFunc(func(_ runtime.Object) ([]byte, error) {
+				return []byte(fmt.Sprintf(`{"metadata":{"$patch":"replace","finalizers":[],"name":"%s","uid":"%s"}}`, p.Name, p.UID)), nil
+			})); err != nil {
+				return false, errors.Wrap(err, "clear PVC finalizers")
+			}
 		}
 
 		return false, nil

pkg/controllers/cluster/util/patch.go

@@ -9,6 +9,7 @@ import (
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apimachinery/pkg/util/strategicpatch"
 	"k8s.io/client-go/kubernetes"
@@ -82,3 +83,16 @@ func PatchService(ctx context.Context, old, new *corev1.Service, kubeClient kube
 	_, err = kubeClient.CoreV1().Services(old.Namespace).Patch(ctx, old.Name, types.StrategicMergePatchType, patchBytes, metav1.PatchOptions{})
 	return err
 }
+
+// The StrategicMergePatchFunc type is an adapter to allow the use of ordinary functions as Strategic Merge Patch.
+type StrategicMergePatchFunc func(obj runtime.Object) ([]byte, error)
+
+// Type returns PatchType of Strategic Merge Patch
+func (f StrategicMergePatchFunc) Type() types.PatchType {
+	return types.StrategicMergePatchType
+}
+
+// Data returns the raw data representing the patch.
+func (f StrategicMergePatchFunc) Data(obj runtime.Object) ([]byte, error) {
+	return f(obj)
+}