Patch service instead of update in service controller

Co-authored-by: Josh Horwitz <horwitzja@gmail.com>

pkg/controller/service/patch.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2019 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 service
+
+import (
+	"encoding/json"
+	"fmt"
+
+	v1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/strategicpatch"
+	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
+)
+
+// patch patches service's Status or ObjectMeta given the origin and
+// updated ones. Change to spec will be ignored.
+func patch(c v1core.CoreV1Interface, oldSvc *v1.Service, newSvc *v1.Service) (*v1.Service, error) {
+	// Reset spec to make sure only patch for Status or ObjectMeta.
+	newSvc.Spec = oldSvc.Spec
+
+	patchBytes, err := getPatchBytes(oldSvc, newSvc)
+	if err != nil {
+		return nil, err
+	}
+
+	updatedSvc, err := c.Services(oldSvc.Namespace).Patch(oldSvc.Name, types.StrategicMergePatchType, patchBytes, "status")
+	if err != nil {
+		return nil, fmt.Errorf("failed to patch %q for svc %s/%s: %v", patchBytes, oldSvc.Namespace, oldSvc.Name, err)
+	}
+	return updatedSvc, nil
+}
+
+func getPatchBytes(oldSvc *v1.Service, newSvc *v1.Service) ([]byte, error) {
+	oldData, err := json.Marshal(oldSvc)
+	if err != nil {
+		return nil, fmt.Errorf("failed to Marshal oldData for svc %s/%s: %v", oldSvc.Namespace, oldSvc.Name, err)
+	}
+
+	newData, err := json.Marshal(newSvc)
+	if err != nil {
+		return nil, fmt.Errorf("failed to Marshal newData for svc %s/%s: %v", newSvc.Namespace, newSvc.Name, err)
+	}
+
+	patchBytes, err := strategicpatch.CreateTwoWayMergePatch(oldData, newData, v1.Service{})
+	if err != nil {
+		return nil, fmt.Errorf("failed to CreateTwoWayMergePatch for svc %s/%s: %v", oldSvc.Namespace, oldSvc.Name, err)
+	}
+	return patchBytes, nil
+}