[#600] Add health metric

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

cmd/s3-gw/app.go

@@ -35,6 +35,8 @@ type (
 		obj layer.Client
 		api api.Handler
 
+		metrics GateMetricsCollector
+
 		maxClients api.MaxClients
 
 		webDone chan struct{}
@@ -45,6 +47,10 @@ type (
 		KeyFile  string
 		CertFile string
 	}
+
+	GateMetricsCollector interface {
+		SetHealth(int32)
+	}
 )
 
 func newApp(ctx context.Context, l *zap.Logger, v *viper.Viper) *App {
@@ -57,6 +63,8 @@ func newApp(ctx context.Context, l *zap.Logger, v *viper.Viper) *App {
 		obj    layer.Client
 		nc     *notifications.Controller
 
+		gateMetrics GateMetricsCollector
+
 		prmPool pool.InitParameters
 
 		reBalance  = defaultRebalanceInterval
@@ -180,6 +188,10 @@ func newApp(ctx context.Context, l *zap.Logger, v *viper.Viper) *App {
 		l.Fatal("could not initialize API handler", zap.Error(err))
 	}
 
+	if v.GetBool(cfgEnableMetrics) {
+		gateMetrics = newGateMetrics()
+	}
+
 	return &App{
 		ctr: ctr,
 		log: l,
@@ -188,6 +200,8 @@ func newApp(ctx context.Context, l *zap.Logger, v *viper.Viper) *App {
 		tls: tls,
 		api: caller,
 
+		metrics: gateMetrics,
+
 		webDone: make(chan struct{}, 1),
 		wrkDone: make(chan struct{}, 1),
 
@@ -215,6 +229,10 @@ func (a *App) Wait() {
 		zap.String("version", version.Version),
 	)
 
+	if a.metrics != nil {
+		a.metrics.SetHealth(1)
+	}
+
 	<-a.webDone // wait for web-server to be stopped
 
 	a.log.Info("application finished")
@@ -238,7 +256,6 @@ func (a *App) Server(ctx context.Context) {
 	router := newS3Router()
 
 	// Attach app-specific routes:
-	//	attachHealthy(router, a.cli)
 	attachMetrics(router, a.cfg, a.log)
 	attachProfiler(router, a.cfg, a.log)
 

cmd/s3-gw/app_healthy.go

@@ -1,46 +1,46 @@
 package main
 
 import (
-	"fmt"
-	"net/http"
-
-	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
-// Healthy is a health check interface.
-type Healthy interface {
-	Status() error
-}
-
 const (
-	healthyState       = "NeoFS S3 Gateway is "
-	hdrContentType     = "Content-Type"
-	defaultContentType = "text/plain; charset=utf-8"
+	namespace      = "neofs_s3_gw"
+	stateSubsystem = "state"
 )
 
-//nolint:deadcode,unused // TODO
-func attachHealthy(r *mux.Router, h Healthy) {
-	healthy := r.PathPrefix(systemPath + "/-").
-		Subrouter().
-		StrictSlash(true)
-
-	healthy.HandleFunc("/ready", func(w http.ResponseWriter, r *http.Request) {
-		w.Header().Set(hdrContentType, defaultContentType)
-		w.WriteHeader(http.StatusOK)
-		_, _ = fmt.Fprintln(w, healthyState+"ready")
-	})
-
-	healthy.HandleFunc("/healthy", func(w http.ResponseWriter, r *http.Request) {
-		code := http.StatusOK
-		msg := "healthy"
-
-		if err := h.Status(); err != nil {
-			msg = "unhealthy: " + err.Error()
-			code = http.StatusBadRequest
+type GateMetrics struct {
+	stateMetrics
 }
 
-		w.Header().Set(hdrContentType, defaultContentType)
-		w.WriteHeader(code)
-		_, _ = fmt.Fprintln(w, healthyState+msg)
-	})
+type stateMetrics struct {
+	healthCheck prometheus.Gauge
+}
+
+func newGateMetrics() *GateMetrics {
+	stateMetric := newStateMetrics()
+	stateMetric.register()
+
+	return &GateMetrics{
+		stateMetrics: stateMetric,
+	}
+}
+
+func newStateMetrics() stateMetrics {
+	return stateMetrics{
+		healthCheck: prometheus.NewGauge(prometheus.GaugeOpts{
+			Namespace: namespace,
+			Subsystem: stateSubsystem,
+			Name:      "health",
+			Help:      "Current S3 gateway state",
+		}),
+	}
+}
+
+func (m stateMetrics) register() {
+	prometheus.MustRegister(m.healthCheck)
+}
+
+func (m stateMetrics) SetHealth(s int32) {
+	m.healthCheck.Set(float64(s))
 }