[#164] metrics: Rename metrics.go -> node.go

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/metrics/node.go

@@ -0,0 +1,43 @@
+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+const namespace = "frostfs_node"
+
+type NodeMetrics struct {
+	objectServiceMetrics
+	engineMetrics
+	stateMetrics
+	epoch prometheus.Gauge
+}
+
+func NewNodeMetrics() *NodeMetrics {
+	objectService := newObjectServiceMetrics()
+	objectService.register()
+
+	engine := newEngineMetrics()
+	engine.register()
+
+	state := newStateMetrics()
+	state.register()
+
+	epoch := prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: namespace,
+		Subsystem: innerRingSubsystem,
+		Name:      "epoch",
+		Help:      "Current epoch as seen by inner-ring node.",
+	})
+	mustRegister(epoch)
+
+	return &NodeMetrics{
+		objectServiceMetrics: objectService,
+		engineMetrics:        engine,
+		stateMetrics:         state,
+		epoch:                epoch,
+	}
+}
+
+// SetEpoch updates epoch metric.
+func (m *NodeMetrics) SetEpoch(epoch uint64) {
+	m.epoch.Set(float64(epoch))
+}