etcdserver/api/v2stats/leader.go
func (fs *FollowerStats) Fail() {
	fs.Lock()
	defer fs.Unlock()
	fs.Counts.Fail++
}
func (fs *FollowerStats) Fail() {
	fs.Lock()
	defer fs.Unlock()
	fs.Counts.Fail++
}
// Fail updates the FollowerStats with an unsuccessful send