client-go: update leader election example

Kubernetes-commit: 8a82b21f46c261ac920074274b213a888f47c256

examples/leader-election/main.go

@@ -0,0 +1,161 @@
+/*
+Copyright 2018 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 main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	clientset "k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
+	"k8s.io/client-go/tools/leaderelection"
+	"k8s.io/client-go/tools/leaderelection/resourcelock"
+	"k8s.io/client-go/transport"
+	"k8s.io/klog"
+)
+
+func buildConfig(kubeconfig string) (*rest.Config, error) {
+	if kubeconfig != "" {
+		cfg, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
+		if err != nil {
+			return nil, err
+		}
+		return cfg, nil
+	}
+
+	cfg, err := rest.InClusterConfig()
+	if err != nil {
+		return nil, err
+	}
+	return cfg, nil
+}
+
+func main() {
+	klog.InitFlags(nil)
+
+	var kubeconfig string
+	var leaseLockName string
+	var leaseLockNamespace string
+	var id string
+
+	flag.StringVar(&kubeconfig, "kubeconfig", "", "absolute path to the kubeconfig file")
+	flag.StringVar(&id, "id", "", "the holder identity name")
+	flag.StringVar(&leaseLockName, "lease-lock-name", "example", "the lease lock resource name")
+	flag.StringVar(&leaseLockNamespace, "lease-lock-namespace", "default", "the lease lock resource namespace")
+	flag.Parse()
+
+	if id == "" {
+		klog.Fatal("unable to get id (missing id flag).")
+	}
+
+	// leader election uses the Kubernetes API by writing to a
+	// lock object, which can be a LeaseLock object (preferred),
+	// a ConfigMap, or an Endpoints (deprecated) object.
+	// Conflicting writes are detected and each client handles those actions
+	// independently.
+	config, err := buildConfig(kubeconfig)
+	if err != nil {
+		klog.Fatal(err)
+	}
+	client := clientset.NewForConfigOrDie(config)
+
+	// we use the Lease lock type since edits to Leases are less common
+	// and fewer objects in the cluster watch "all Leases".
+	lock := &resourcelock.LeaseLock{
+		LeaseMeta: metav1.ObjectMeta{
+			Name:      leaseLockName,
+			Namespace: leaseLockNamespace,
+		},
+		Client: client.CoordinationV1(),
+		LockConfig: resourcelock.ResourceLockConfig{
+			Identity: id,
+		},
+	}
+
+	// use a Go context so we can tell the leaderelection code when we
+	// want to step down
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// use a client that will stop allowing new requests once the context ends
+	config.Wrap(transport.ContextCanceller(ctx, fmt.Errorf("the leader is shutting down")))
+
+	// listen for interrupts or the Linux SIGTERM signal and cancel
+	// our context, which the leader election code will observe and
+	// step down
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, os.Interrupt, syscall.SIGTERM)
+	go func() {
+		<-ch
+		log.Printf("Received termination, signaling shutdown")
+		cancel()
+	}()
+
+	// start the leader election code loop
+	leaderelection.RunOrDie(ctx, leaderelection.LeaderElectionConfig{
+		Lock: lock,
+		// IMPORTANT: you MUST ensure that any code you have that
+		// is protected by the lease must terminate **before**
+		// you call cancel. Otherwise, you could have a background
+		// loop still running and another process could
+		// get elected before your background loop finished, violating
+		// the stated goal of the lease.
+		ReleaseOnCancel: true,
+		LeaseDuration:   60 * time.Second,
+		RenewDeadline:   15 * time.Second,
+		RetryPeriod:     5 * time.Second,
+		Callbacks: leaderelection.LeaderCallbacks{
+			OnStartedLeading: func(ctx context.Context) {
+				// we're notified when we start - this is where you would
+				// usually put your code
+				klog.Infof("%s: leading", id)
+			},
+			OnStoppedLeading: func() {
+				// we can do cleanup here, or after the RunOrDie method
+				// returns
+				klog.Infof("%s: lost", id)
+			},
+			OnNewLeader: func(identity string) {
+				// we're notified when new leader elected
+				if identity == id {
+					// I just got the lock
+					return
+				}
+				klog.Infof("new leader elected: %v", identity)
+			},
+		},
+	})
+
+	// because the context is closed, the client should report errors
+	_, err = client.CoordinationV1().Leases(leaseLockNamespace).Get(leaseLockName, metav1.GetOptions{})
+	if err == nil || !strings.Contains(err.Error(), "the leader is shutting down") {
+		log.Fatalf("%s: expected to get an error when trying to make a client call: %v", id, err)
+	}
+
+	// we no longer hold the lease, so perform any cleanup and then
+	// exit
+	log.Printf("%s: done", id)
+}