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package main
import (
"context"
"flag"
"os"
"os/signal"
"syscall"
"time"
"github.com/google/uuid"
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/klog/v2"
)
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
// kubeconfig 指定了kubernetes集群的配置文文件路径
flag.StringVar(&kubeconfig, "kubeconfig", "", "absolute path to the kubeconfig file")
// 锁的拥有者的ID，如果没有传参数进来，就随机生成一个
flag.StringVar(&id, "id", uuid.New().String(), "the holder identity name")
// 锁的ID，对应kubernetes中资源的name
flag.StringVar(&leaseLockName, "lease-lock-name", "", "the lease lock resource name")
// 锁的命名空间
flag.StringVar(&leaseLockNamespace, "lease-lock-namespace", "", "the lease lock resource namespace")
// 解析命令行参数
flag.Parse()
if leaseLockName == "" {
klog.Fatal("unable to get lease lock resource name (missing lease-lock-name flag).")
}
if leaseLockNamespace == "" {
klog.Fatal("unable to get lease lock resource namespace (missing lease-lock-namespace 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)
}
// 获取kubernetes集群的客户端，如果获取不到，就抛异常退出
client := clientset.NewForConfigOrDie(config)
// 模拟Controller的逻辑代码
run := func(ctx context.Context) {
// complete your controller loop here
klog.Info("Controller loop...")
// 不退出
select {}
}
// 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()
// listen for interrupts or the Linux SIGTERM signal and cancel
// our context, which the leader election code will observe and
// step down
// 处理系统的系统，收到SIGTERM信号后，会退出进程
ch := make(chan os.Signal, 1)
signal.Notify(ch, os.Interrupt, syscall.SIGTERM)
go func() {
<-ch
klog.Info("Received termination, signaling shutdown")
cancel()
}()
// we use the Lease lock type since edits to Leases are less common
// and fewer objects in the cluster watch "all Leases".
// 根据参数，生成锁。这里使用的Lease这种类型资源作为锁
lock := &resourcelock.LeaseLock{
LeaseMeta: metav1.ObjectMeta{
Name: leaseLockName,
Namespace: leaseLockNamespace,
},
// 跟kubernetes集群关联起来
Client: client.CoordinationV1(),
LockConfig: resourcelock.ResourceLockConfig{
Identity: id,
},
}
// start the leader election code loop
// 注意，选举逻辑启动时候，会传入ctx参数，如果ctx对应的cancel函数被调用，那么选举也会结束
leaderelection.RunOrDie(ctx, leaderelection.LeaderElectionConfig{
// 选举使用的锁
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.
//主动放弃leader，当ctx canceled的时候
ReleaseOnCancel: true,
LeaseDuration: 60 * time.Second, // 选举的任期，60s一个任期，如果在60s后没有renew，那么leader就会释放锁，重新选举
RenewDeadline: 15 * time.Second, // renew的请求的超时时间
RetryPeriod: 5 * time.Second, // leader获取到锁后，renew leadership的间隔。非leader，抢锁成为leader的间隔（有1.2的jitter因子，详细看代码）
// 回调函数的注册
Callbacks: leaderelection.LeaderCallbacks{
// 成为leader的回调
OnStartedLeading: func(ctx context.Context) {
// we're notified when we start - this is where you would
// usually put your code
// 运行controller的逻辑
run(ctx)
},
OnStoppedLeading: func() {
// we can do cleanup here
// 退出leader的
klog.Infof("leader lost: %s", id)
os.Exit(0)
},
OnNewLeader: func(identity string) {
// 有新的leader当选
// we're notified when new leader elected
if identity == id {
// I just got the lock
return
}
klog.Infof("new leader elected: %s", identity)
},
},
})
}
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