Kubernetes源码分析:选举实现

type Interface interface {
	// Get returns the LeaderElectionRecord
	Get() (*LeaderElectionRecord, []byte, error)

	// Create attempts to create a LeaderElectionRecord
	Create(ler LeaderElectionRecord) error

	// Update will update and existing LeaderElectionRecord
	Update(ler LeaderElectionRecord) error

	// RecordEvent is used to record events
	RecordEvent(string)

	// Identity will return the locks Identity
	Identity() string

	// Describe is used to convert details on current resource lock
	// into a string
	Describe() string
}

type LeaderElectionRecord struct {
	// HolderIdentity is the ID that owns the lease. If empty, no one owns this lease and
	// all callers may acquire. Versions of this library prior to Kubernetes 1.14 will not
	// attempt to acquire leases with empty identities and will wait for the full lease
	// interval to expire before attempting to reacquire. This value is set to empty when
    // a client voluntarily steps down.
    // 候选人的唯一ID
    HolderIdentity       string      `json:"holderIdentity"`
    // 下一轮间隔
    LeaseDurationSeconds int         `json:"leaseDurationSeconds"`
    // 竞选成功的时间
    AcquireTime          metav1.Time `json:"acquireTime"`
    // 连任时间
    RenewTime            metav1.Time `json:"renewTime"`
    // 竞态计数器, 不同的候选人竞选成功后, 会将该值+1
	LeaderTransitions    int         `json:"leaderTransitions"`
}

now := metav1.Now()
leaderElectionRecord := rl.LeaderElectionRecord{
    HolderIdentity:       le.config.Lock.Identity(),
    LeaseDurationSeconds: int(le.config.LeaseDuration / time.Second),
    RenewTime:            now,
    AcquireTime:          now,
}

oldLeaderElectionRecord, oldLeaderElectionRawRecord, err := le.config.Lock.Get()
if err != nil {
    if !errors.IsNotFound(err) {
        klog.Errorf("error retrieving resource lock %v: %v", le.config.Lock.Describe(), err)
        return false
    }
    if err = le.config.Lock.Create(leaderElectionRecord); err != nil {
        klog.Errorf("error initially creating leader election record: %v", err)
        return false
    }
    le.observedRecord = leaderElectionRecord
    le.observedTime = le.clock.Now()
    return true
}

// 2. Record obtained, check the Identity & Time
if !bytes.Equal(le.observedRawRecord, oldLeaderElectionRawRecord) {
    le.observedRecord = *oldLeaderElectionRecord
    le.observedRawRecord = oldLeaderElectionRawRecord
    le.observedTime = le.clock.Now()
}
if len(oldLeaderElectionRecord.HolderIdentity) > 0 &&
    le.observedTime.Add(le.config.LeaseDuration).After(now.Time) &&
    !le.IsLeader() {
    klog.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 le.IsLeader() {
    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 {
    klog.Errorf("Failed to update lock: %v", err)
    return false
}
le.observedRecord = leaderElectionRecord
le.observedTime = le.clock.Now()
return true