etcdhttp: add metrics.go for metrics, health handler

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

etcdserver/api/etcdhttp/metrics.go

@@ -0,0 +1,91 @@
+// Copyright 2017 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package etcdhttp
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/coreos/etcd/etcdserver"
+	"github.com/coreos/etcd/etcdserver/etcdserverpb"
+	"github.com/coreos/etcd/raft"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	pathMetrics = "/metrics"
+	pathHealth  = "/health"
+)
+
+// HandleMetricsHealth registers metrics and health handlers.
+func HandleMetricsHealth(mux *http.ServeMux, srv *etcdserver.EtcdServer) {
+	mux.Handle(pathMetrics, prometheus.Handler())
+	mux.Handle(pathHealth, newHealthHandler(srv))
+}
+
+// HandlePrometheus registers prometheus handler on '/metrics'.
+func HandlePrometheus(mux *http.ServeMux) {
+	mux.Handle(pathMetrics, prometheus.Handler())
+}
+
+// HandleHealth registers health handler on '/health'.
+func HandleHealth(mux *http.ServeMux, srv *etcdserver.EtcdServer) {
+	mux.Handle(pathHealth, newHealthHandler(srv))
+}
+
+// newHealthHandler handles '/health' requests.
+func newHealthHandler(srv *etcdserver.EtcdServer) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			w.Header().Set("Allow", http.MethodGet)
+			http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		h := checkHealth(srv)
+		d := []byte(fmt.Sprintf(`{"health": "%v"}`, h.Health))
+		if !h.Health {
+			http.Error(w, string(d), http.StatusServiceUnavailable)
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		w.Write(d)
+	}
+}
+
+type health struct {
+	Health bool `json:"health"`
+}
+
+func checkHealth(srv *etcdserver.EtcdServer) health {
+	h := health{Health: false}
+	if len(srv.Alarms()) > 0 {
+		// TODO: provide alarm lists
+		return h
+	}
+
+	if uint64(srv.Leader()) == raft.None {
+		return h
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	_, err := srv.Do(ctx, etcdserverpb.Request{Method: "QGET"})
+	cancel()
+
+	h.Health = err == nil
+	return h
+}