client-go: Add CRUD Deployment sample

This sample adds sample code for create/list/replace/delete operations for
Deployment resource for client-go library. This patch also contains
documentation explaining what the example application does and how it can be
executed.

This patch is part of the body of work improving the client library samples.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

Kubernetes-commit: d75710f9f4d2e74979f6da07de31b02fae0392b0

examples/create-update-delete-deployment/main.go

@@ -0,0 +1,165 @@
+/*
+Copyright 2017 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.
+*/
+
+// Note: the example only works with the code within the same release/branch.
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+
+	"k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+	apiv1 "k8s.io/client-go/pkg/api/v1"
+	appsv1beta1 "k8s.io/client-go/pkg/apis/apps/v1beta1"
+	"k8s.io/client-go/tools/clientcmd"
+	// Uncomment the following line to load the gcp plugin (only required to authenticate against GKE clusters).
+	// _ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
+)
+
+func main() {
+	kubeconfig := flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
+	flag.Parse()
+	if *kubeconfig == "" {
+		panic("-kubeconfig not specified")
+	}
+	config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
+	if err != nil {
+		panic(err)
+	}
+	clientset, err := kubernetes.NewForConfig(config)
+	if err != nil {
+		panic(err)
+	}
+
+	deploymentsClient := clientset.AppsV1beta1().Deployments(apiv1.NamespaceDefault)
+
+	deployment := &appsv1beta1.Deployment{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: "demo-deployment",
+		},
+		Spec: appsv1beta1.DeploymentSpec{
+			Replicas: int32Ptr(2),
+			Template: apiv1.PodTemplateSpec{
+				ObjectMeta: metav1.ObjectMeta{
+					Labels: map[string]string{
+						"app": "demo",
+					},
+				},
+				Spec: apiv1.PodSpec{
+					Containers: []apiv1.Container{
+						{
+							Name:  "web",
+							Image: "nginx:1.13",
+							Ports: []apiv1.ContainerPort{
+								{
+									Name:          "http",
+									Protocol:      apiv1.ProtocolTCP,
+									ContainerPort: 80,
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	// Create Deployment
+	fmt.Println("Creating deployment...")
+	result, err := deploymentsClient.Create(deployment)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("Created deployment %q.\n", result.GetObjectMeta().GetName())
+
+	// Update Deployment
+	prompt()
+	fmt.Println("Updating deployment...")
+	//    You have two options to Update() this Deployment:
+	//
+	//    1. Modify the "deployment" variable and call: Update(deployment).
+	//       This works like the "kubectl replace" command and it overwrites/loses changes
+	//       made by other clients between you Create() and Update() the object.
+	//    2. Modify the "result" returned by Create()/Get() and retry Update(result) until
+	//       you no longer get a conflict error. This way, you can preserve changes made
+	//       by other clients between Create() and Update(). This is implemented below:
+
+	for {
+		result.Spec.Replicas = int32Ptr(1)                    // reduce replica count
+		result.Spec.Template.Annotations = map[string]string{ // add annotations
+			"foo": "bar",
+		}
+
+		if _, err := deploymentsClient.Update(result); errors.IsConflict(err) {
+			// Deployment is modified in the meanwhile, query the latest version
+			// and modify the retrieved object.
+			fmt.Println("encountered conflict, retrying")
+			result, err = deploymentsClient.Get("demo-deployment", metav1.GetOptions{})
+			if err != nil {
+				panic(fmt.Errorf("Get failed: %+v", err))
+			}
+		} else if err != nil {
+			panic(err)
+		} else {
+			break
+		}
+
+		// TODO: You should sleep here with an exponential backoff to avoid
+		// exhausting the apiserver, and add a limit/timeout on the retries to
+		// avoid getting stuck in this loop indefintiely.
+	}
+	fmt.Println("Updated deployment...")
+
+	// List Deployments
+	prompt()
+	fmt.Printf("Listing deployments in namespace %q:\n", apiv1.NamespaceDefault)
+	list, err := deploymentsClient.List(metav1.ListOptions{})
+	if err != nil {
+		panic(err)
+	}
+	for _, d := range list.Items {
+		fmt.Printf(" * %s (%d replicas)\n", d.Name, *d.Spec.Replicas)
+	}
+
+	// Delete Deployment
+	prompt()
+	fmt.Println("Deleting deployment...")
+	deletePolicy := metav1.DeletePropagationForeground
+	if err := deploymentsClient.Delete("demo-deployment", &metav1.DeleteOptions{
+		PropagationPolicy: &deletePolicy,
+	}); err != nil {
+		panic(err)
+	}
+	fmt.Println("Deleted deployment.")
+}
+
+func prompt() {
+	fmt.Printf("-> Press Return key to continue.")
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		break
+	}
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+	fmt.Println()
+}
+
+func int32Ptr(i int32) *int32 { return &i }