replication.go
func (s *followerReplication) LastContact() time.Time {
	s.lastContactLock.RLock()
	last := s.lastContact
	s.lastContactLock.RUnlock()
	return last
}
func (s *followerReplication) LastContact() time.Time {
	s.lastContactLock.RLock()
	last := s.lastContact
	s.lastContactLock.RUnlock()
	return last
}
// LastContact returns the time of last contact.