leader选举源码分析

kube-sheduler leader 选举代码分析

所使用的包clinet-go 模块中的tools/leaderelection 包

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// If leader election is enabled, run via LeaderElector until done and exit.
if c.LeaderElection != nil {
// 设置callbacks 方法started/stopped
c.LeaderElection.Callbacks = leaderelection.LeaderCallbacks{
OnStartedLeading: run,
OnStoppedLeading: func() {
utilruntime.HandleError(fmt.Errorf("lost master"))
},
}
leaderElector, err := leaderelection.NewLeaderElector(*c.LeaderElection)
if err != nil {
return fmt.Errorf("couldn't create leader elector: %v", err)
}
// 启动选举方法
leaderElector.Run()
return fmt.Errorf("lost lease")
}
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// 使用client-go 模块中的tools/leaderelection包
// Run starts the leader election loop
func (le *LeaderElector) Run() {
// 设置函数返回之前执行的callbacks方法
defer func() {
runtime.HandleCrash()
le.config.Callbacks.OnStoppedLeading()
}()
// 获取和选举leader信息 如果不是leader 则一直循环选举等待
le.acquire()
stop := make(chan struct{})
// 运行scheduler 的逻辑代码 stop 管道设置为阻塞状态
go le.config.Callbacks.OnStartedLeading(stop)
// 选举新的leader
le.renew()
close(stop)
}
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// acquire loops calling tryAcquireOrRenew and returns immediately when tryAcquireOrRenew succeeds.
// 周期性选举leader,直到自己成为leader后才推出循环
func (le *LeaderElector) acquire() {
stop := make(chan struct{})
// 输出命名空间和名称eg: kube-system/kube-scheduler
desc := le.config.Lock.Describe()
glog.Infof("attempting to acquire leader lease %v...", desc)
// 调用apimachinery 模块中的wait包中JitterUntil循环执行函数
wait.JitterUntil(func() {
succeeded := le.tryAcquireOrRenew()
le.maybeReportTransition()
//
if !succeeded {
glog.V(4).Infof("failed to acquire lease %v", desc)
return
}
le.config.Lock.RecordEvent("became leader")
glog.Infof("successfully acquired lease %v", desc)
//
close(stop)
}, le.config.RetryPeriod, JitterFactor, true, stop)
}
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// tryAcquireOrRenew tries to acquire a leader lease if it is not already acquired,
// else it tries to renew the lease if it has already been acquired. Returns true
// on success else returns false.
// 获取leader信息是否是本机
func (le *LeaderElector) tryAcquireOrRenew() bool {
now := metav1.Now()
leaderElectionRecord := rl.LeaderElectionRecord{
HolderIdentity: le.config.Lock.Identity(),
LeaseDurationSeconds: int(le.config.LeaseDuration / time.Second),
RenewTime: now,
AcquireTime: now,
}
// 1. obtain or create the ElectionRecord
oldLeaderElectionRecord, err := le.config.Lock.Get()
if err != nil {
if !errors.IsNotFound(err) {
glog.Errorf("error retrieving resource lock %v: %v", le.config.Lock.Describe(), err)
return false
}
if err = le.config.Lock.Create(leaderElectionRecord); err != nil {
glog.Errorf("error initially creating leader election record: %v", err)
return false
}
le.observedRecord = leaderElectionRecord
le.observedTime = time.Now()
return true
}
// 2. Record obtained, check the Identity & Time
if !reflect.DeepEqual(le.observedRecord, *oldLeaderElectionRecord) {
le.observedRecord = *oldLeaderElectionRecord
le.observedTime = time.Now()
}
if le.observedTime.Add(le.config.LeaseDuration).After(now.Time) &&
oldLeaderElectionRecord.HolderIdentity != le.config.Lock.Identity() {
glog.V(4).Infof("lock is held by %v and has not yet expired", oldLeaderElectionRecord.HolderIdentity)
return false
}
// 3. We're going to try to update. The leaderElectionRecord is set to it's default
// here. Let's correct it before updating.
if oldLeaderElectionRecord.HolderIdentity == le.config.Lock.Identity() {
leaderElectionRecord.AcquireTime = oldLeaderElectionRecord.AcquireTime
leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions
} else {
leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions + 1
}
// update the lock itself
if err = le.config.Lock.Update(leaderElectionRecord); err != nil {
glog.Errorf("Failed to update lock: %v", err)
return false
}
le.observedRecord = leaderElectionRecord
le.observedTime = time.Now()
return true
}
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// renew loops calling tryAcquireOrRenew and returns immediately when tryAcquireOrRenew fails.
// 间歇性获取leader信息是否是本机
func (le *LeaderElector) renew() {
stop := make(chan struct{})
wait.Until(func() {
err := wait.Poll(le.config.RetryPeriod, le.config.RenewDeadline, func() (bool, error) {
return le.tryAcquireOrRenew(), nil
})
le.maybeReportTransition()
desc := le.config.Lock.Describe()
if err == nil {
glog.V(4).Infof("successfully renewed lease %v", desc)
return
}
le.config.Lock.RecordEvent("stopped leading")
glog.Infof("failed to renew lease %v: %v", desc, err)
close(stop)
}, 0, stop)
}