Leaderlease may cause unnecessary stepping down of leaders in the cluster

[zivfuture]

Why are LeaderLeadseTimeout and ElectTimeout inconsistent?, the source code here:

raft/raft.go

Line 937 in 8f99c15

maxDiff := r.checkLeaderLease()

// checkLeaderLease is used to check if we can contact a quorum of nodes
// within the last leader lease interval. If not, we need to step down,
// as we may have lost connectivity. Returns the maximum duration without
// contact. This must only be called from the main thread.
func (r *Raft) checkLeaderLease() time.Duration {
	// Track contacted nodes, we can always contact ourself
	contacted := 0

	// Store lease timeout for this one check invocation as we need to refer to it
	// in the loop and would be confusing if it ever becomes reloadable and
	// changes between iterations below.
	leaseTimeout := r.config().LeaderLeaseTimeout

	// Check each follower
	var maxDiff time.Duration
	now := time.Now()
	for _, server := range r.configurations.latest.Servers {
		if server.Suffrage == Voter {
			if server.ID == r.localID {
				contacted++
				continue
			}
			f := r.leaderState.replState[server.ID]
			diff := now.Sub(f.LastContact())
			if diff <= leaseTimeout {
				contacted++
				if diff > maxDiff {
					maxDiff = diff
				}
			} else {
				// Log at least once at high value, then debug. Otherwise it gets very verbose.
				if diff <= 3*leaseTimeout {
					r.logger.Warn("failed to contact", "server-id", server.ID, "time", diff)
				} else {
					r.logger.Debug("failed to contact", "server-id", server.ID, "time", diff)
				}
			}
			metrics.AddSample([]string{"raft", "leader", "lastContact"}, float32(diff/time.Millisecond))
		}
	}

	// Verify we can contact a quorum
	quorum := r.quorumSize()
	if contacted < quorum {
		r.logger.Warn("failed to contact quorum of nodes, stepping down")

               //some questions here  <----------------------
		r.setState(Follower)
		metrics.IncrCounter([]string{"raft", "transition", "leader_lease_timeout"}, 1)
	}
	return maxDiff
}

As shown in the image below, in some cases, the leader does not need to step down .but here he has stepped down