kubernetes Leader Election Example

原文链接：https://sourcegraph.com/github.com/kubernetes/client-go@7f988d725c5d73e1cd4d7cc6ea7f964026035903/-/blob/examples/leader-election/main.go

/*
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)
}

编译：

# first terminal 
go run *.go -kubeconfig=/my/config -logtostderr=true -id=1

# second terminal 
go run *.go -kubeconfig=/my/config -logtostderr=true -id=2

# third terminal
go run *.go -kubeconfig=/my/config -logtostderr=true -id=3