etcdserver/api/etcdhttp/metrics.go
func checkHealth(srv etcdserver.ServerV2) Health {
	h := Health{Health: "true"}

	as := srv.Alarms()
	if len(as) > 0 {
		h.Health = "false"
	}

	if h.Health == "true" {
		if uint64(srv.Leader()) == raft.None {
			h.Health = "false"
		}
	}

	if h.Health == "true" {
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		_, err := srv.Do(ctx, etcdserverpb.Request{Method: "QGET"})
		cancel()
		if err != nil {
			h.Health = "false"
		}
	}

	if h.Health == "true" {
		healthSuccess.Inc()
	} else {
		healthFailed.Inc()
	}
	return h
}
func checkHealth(srv etcdserver.ServerV2) Health {
	h := Health{Health: "true"}

	as := srv.Alarms()
	if len(as) > 0 {
		h.Health = "false"
	}

	if h.Health == "true" {
		if uint64(srv.Leader()) == raft.None {
			h.Health = "false"
		}
	}

	if h.Health == "true" {
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		_, err := srv.Do(ctx, etcdserverpb.Request{Method: "QGET"})
		cancel()
		if err != nil {
			h.Health = "false"
		}
	}

	if h.Health == "true" {
		healthSuccess.Inc()
	} else {
		healthFailed.Inc()
	}
	return h
}
// TODO: server NOSPACE, etcdserver.ErrNoLeader in health API