TUN-9511: Add metrics for virtual DNS origin

Closes TUN-9511

ingress/origins/metrics.go

@@ -0,0 +1,40 @@
+package origins
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	namespace = "cloudflared"
+	subsystem = "virtual_origins"
+)
+
+type Metrics interface {
+	IncrementDNSUDPRequests()
+	IncrementDNSTCPRequests()
+}
+
+type metrics struct {
+	dnsResolverRequests *prometheus.CounterVec
+}
+
+func (m *metrics) IncrementDNSUDPRequests() {
+	m.dnsResolverRequests.WithLabelValues("udp").Inc()
+}
+
+func (m *metrics) IncrementDNSTCPRequests() {
+	m.dnsResolverRequests.WithLabelValues("tcp").Inc()
+}
+
+func NewMetrics(registerer prometheus.Registerer) Metrics {
+	m := &metrics{
+		dnsResolverRequests: prometheus.NewCounterVec(prometheus.CounterOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "dns_requests_total",
+			Help:      "Total count of DNS requests that have been proxied to the virtual DNS resolver origin",
+		}, []string{"protocol"}),
+	}
+	registerer.MustRegister(m.dnsResolverRequests)
+	return m
+}