avoiding 409 conflict errors with strategic merge patch

avoid-conflicts-poc.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	corev1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/apimachinery/pkg/util/strategicpatch"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/tools/clientcmd"
)

func main() {
	// Load kubeconfig
	config, err := clientcmd.BuildConfigFromFlags("", clientcmd.RecommendedHomeFile)
	if err != nil {
		panic(err.Error())
	}

	// Create a clientset
	clientset, err := kubernetes.NewForConfig(config)
	if err != nil {
		panic(err.Error())
	}

	// Define a BusyBox pod
	pod := &corev1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			Name:      "busybox-pod",
			Namespace: "default",
		},
		Spec: corev1.PodSpec{
			Containers: []corev1.Container{
				{
					Name:    "busybox",
					Image:   "busybox",
					Command: []string{"sh", "-c", "sleep 3600"},
				},
			},
		},
	}

	// Create the pod
	createdPod, err := clientset.CoreV1().Pods("default").Create(context.TODO(), pod, metav1.CreateOptions{})
	if err != nil {
		panic(err.Error())
	}

	// Create a new pod object with the updated owner reference
	updatedPod := createdPod.DeepCopy()
	updatedPod.OwnerReferences = []metav1.OwnerReference{
		{
			APIVersion: "v1",
			Kind:       "Pod",
			Name:       createdPod.Name,
			UID:        createdPod.UID,
		},
	}

	// Marshal the original and updated pod to JSON
	originalJSON, err := json.Marshal(createdPod)
	if err != nil {
		panic(err.Error())
	}

	updatedJSON, err := json.Marshal(updatedPod)
	if err != nil {
		panic(err.Error())
	}

	// Create the strategic merge patch
	patchBytes, err := strategicpatch.CreateTwoWayMergePatch(originalJSON, updatedJSON, corev1.Pod{})
	if err != nil {
		panic(err.Error())
	}

	fmt.Println("created pod version: ", createdPod.ResourceVersion)
	getPod, err := clientset.CoreV1().Pods("default").Get(context.TODO(), pod.Name, metav1.GetOptions{})
	if err != nil {
		panic(err.Error())
	}
	fmt.Println("pod version now: ", getPod.ResourceVersion)

	// Update the pod with a strategic merge patch
	_, err = clientset.CoreV1().Pods("default").Patch(context.TODO(), createdPod.Name, types.StrategicMergePatchType, patchBytes, metav1.PatchOptions{})
	if err != nil {
		panic(fmt.Errorf("update failed: %v", err))
	}
	fmt.Printf("Updated pod %s with owner reference\n", createdPod.Name)

	createdPod.Annotations = map[string]string{

		"apiVersion": "v1",
		"kind":       "Pod",
		"name":       createdPod.Name,
		"uid":        string(createdPod.UID),
	}

	fmt.Println("created pod version: ", createdPod.ResourceVersion)
	getPod, err = clientset.CoreV1().Pods("default").Get(context.TODO(), pod.Name, metav1.GetOptions{})
	if err != nil {
		panic(err.Error())
	}
	fmt.Println("pod version now: ", getPod.ResourceVersion)
	_, err = clientset.CoreV1().Pods("default").Update(context.TODO(), createdPod, metav1.UpdateOptions{})
	if err != nil {
		if errors.IsConflict(err) {
			fmt.Println("conflict error found")
		}
		panic(fmt.Errorf("update failed: %v", err))
	}

}