consul/internal/controller/lease.go

package controller

// Lease is used to ensure controllers are run as singletons (i.e. one leader-
// elected instance per cluster).
//
// Currently, this is just an abstraction over Raft leadership. In the future,
// we'll build a backend-agnostic leasing system into the Resource Service which
// will allow us to balance controllers between many servers.
type Lease interface {
	// Held returns whether we are the current lease-holders.
	Held() bool

	// Changed returns a channel on which you can receive notifications whenever
	// the lease is acquired or lost.
	Changed() <-chan struct{}
}

type raftLease struct {
	m  *Manager
	ch <-chan struct{}
}

func (l *raftLease) Held() bool               { return l.m.raftLeader.Load() }
func (l *raftLease) Changed() <-chan struct{} { return l.ch }

type eternalLease struct{}

func (eternalLease) Held() bool               { return true }
func (eternalLease) Changed() <-chan struct{} { return nil }