[#77] Add metrics for HTTP endpoint status

Signed-off-by: Marina Biryukova <m.biryukova@yadro.com>

metrics/metrics.go

@@ -10,9 +10,10 @@ import (
 )
 
 const (
-	namespace      = "frostfs_http_gw"
-	stateSubsystem = "state"
-	poolSubsystem  = "pool"
+	namespace       = "frostfs_http_gw"
+	stateSubsystem  = "state"
+	poolSubsystem   = "pool"
+	serverSubsystem = "server"
 )
 
 const (
@@ -60,9 +61,14 @@ type StatisticScraper interface {
 	Statistic() pool.Statistic
 }
 
+type serverMetrics struct {
+	endpointHealth *prometheus.GaugeVec
+}
+
 type GateMetrics struct {
 	stateMetrics
 	poolMetricsCollector
+	serverMetrics
 }
 
 type stateMetrics struct {
@@ -87,15 +93,20 @@ func NewGateMetrics(p StatisticScraper) *GateMetrics {
 	poolMetric := newPoolMetricsCollector(p)
 	poolMetric.register()
 
+	serverMetric := newServerMetrics()
+	serverMetric.register()
+
 	return &GateMetrics{
 		stateMetrics:         *stateMetric,
 		poolMetricsCollector: *poolMetric,
+		serverMetrics:        *serverMetric,
 	}
 }
 
 func (g *GateMetrics) Unregister() {
 	g.stateMetrics.unregister()
 	prometheus.Unregister(&g.poolMetricsCollector)
+	g.serverMetrics.unregister()
 }
 
 func newStateMetrics() *stateMetrics {
@@ -192,6 +203,28 @@ func (m *poolMetricsCollector) updateRequestsDuration(node pool.NodeStatistic) {
 	m.requestDuration.WithLabelValues(node.Address(), methodCreateSession).Set(float64(node.AverageCreateSession().Milliseconds()))
 }
 
+func newServerMetrics() *serverMetrics {
+	return &serverMetrics{
+		endpointHealth: mustNewGaugeVec(appMetricsDesc[serverSubsystem][healthMetric]),
+	}
+}
+
+func (m serverMetrics) register() {
+	prometheus.MustRegister(m.endpointHealth)
+}
+
+func (m serverMetrics) unregister() {
+	prometheus.Unregister(m.endpointHealth)
+}
+
+func (m serverMetrics) MarkHealthy(endpoint string) {
+	m.endpointHealth.WithLabelValues(endpoint).Set(float64(1))
+}
+
+func (m serverMetrics) MarkUnhealthy(endpoint string) {
+	m.endpointHealth.WithLabelValues(endpoint).Set(float64(0))
+}
+
 // NewPrometheusService creates a new service for gathering prometheus metrics.
 func NewPrometheusService(log *zap.Logger, cfg Config) *Service {
 	if log == nil {