monitoring: add monitoring package for Prometheus metric exports.

monitoring/monitoring_on.go

@@ -0,0 +1,45 @@
+// +build monitoring
+
+package monitoring
+
+import (
+	"net/http"
+	"sync"
+
+	"google.golang.org/grpc"
+
+	"github.com/grpc-ecosystem/go-grpc-prometheus"
+	"github.com/lightningnetwork/lnd/lncfg"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var started sync.Once
+
+// GetPromInterceptors returns the set of interceptors for Prometheus
+// monitoring.
+func GetPromInterceptors() ([]grpc.UnaryServerInterceptor, []grpc.StreamServerInterceptor) {
+	unaryInterceptors := []grpc.UnaryServerInterceptor{
+		grpc_prometheus.UnaryServerInterceptor,
+	}
+	streamInterceptors := []grpc.StreamServerInterceptor{
+		grpc_prometheus.StreamServerInterceptor,
+	}
+	return unaryInterceptors, streamInterceptors
+}
+
+// ExportPrometheusMetrics sets server options, registers gRPC metrics and
+// launches the Prometheus exporter on the specified address.
+func ExportPrometheusMetrics(grpcServer *grpc.Server, cfg lncfg.Prometheus) error {
+	started.Do(func() {
+		log.Infof("Prometheus exporter started on %v/metrics", cfg.Listen)
+
+		grpc_prometheus.Register(grpcServer)
+
+		http.Handle("/metrics", promhttp.Handler())
+		go func() {
+			http.ListenAndServe(cfg.Listen, nil)
+		}()
+	})
+
+	return nil
+}