rpcserver+monitoring/config: enable Prometheus monitoring.

Start the Prometheus exporter in rpcserver.go if monitoring is enabled through the
build tag. Also allow users to specify what address they want the Prometheus
exporter to be listening on.

config.go

@@ -307,6 +307,8 @@ type config struct {
 	Workers *lncfg.Workers `group:"workers" namespace:"workers"`
 
 	Caches *lncfg.Caches `group:"caches" namespace:"caches"`
+
+	Prometheus *lncfg.PrometheusConfig `group:"prometheus" namespace:"prometheus"`
 }
 
 // loadConfig initializes and parses the config using a config file and command

lncfg/monitoring_off.go

@@ -0,0 +1,7 @@
+// !build monitoring
+
+package lncfg
+
+type PrometheusConfig struct {
+	ListenAddr string `long:"listenaddr" description:"the interface we should listen on for prometheus"`
+}

lncfg/monitoring_on.go

@@ -0,0 +1,11 @@
+// +build monitoring
+
+package lncfg
+
+// PrometheusConfig is the set of configuration data that specifies
+// the listening address of the Prometheus exporter.
+type PrometheusConfig struct {
+	// ListenAddr is the listening address that we should use to allow the
+	// main Prometheus server to scrape our metrics.
+	ListenAddr string `long:"listenaddr" description:"the interface we should listen on for prometheus"`
+}

rpcserver.go

@@ -45,6 +45,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/macaroons"
+	"github.com/lightningnetwork/lnd/monitoring"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/signal"
 	"github.com/lightningnetwork/lnd/sweep"
@@ -529,24 +530,9 @@ func newRPCServer(s *server, macService *macaroons.Service,
 		}
 	}
 
-	// If macaroons aren't disabled (a non-nil service), then we'll set up
-	// our set of interceptors which will allow us handle the macaroon
-	// authentication in a single location .
-	if macService != nil {
-		unaryInterceptor := grpc.UnaryInterceptor(
-			macService.UnaryServerInterceptor(permissions),
-		)
-		streamInterceptor := grpc.StreamInterceptor(
-			macService.StreamServerInterceptor(permissions),
-		)
-
-		serverOpts = append(serverOpts,
-			unaryInterceptor, streamInterceptor,
-		)
-	}
-
 	// Finally, with all the pre-set up complete,  we can create the main
 	// gRPC server, and register the main lnrpc server along side.
+	serverOpts = monitoring.GetServerOpts(macService, permissions, serverOpts)
 	grpcServer := grpc.NewServer(serverOpts...)
 	rootRPCServer := &rpcServer{
 		restDialOpts:  restDialOpts,
@@ -615,6 +601,13 @@ func (r *rpcServer) Start() error {
 		}()
 	}
 
+	// If monitoring is enabled, start the Prometheus exporter.
+	if monitoring.Enabled {
+		monitoring.ExportPrometheusMetrics(
+			r.grpcServer, cfg.Prometheus.ListenAddr,
+		)
+	}
+
 	// Finally, start the REST proxy for our gRPC server above. We'll ensure
 	// we direct LND to connect to its loopback address rather than a
 	// wildcard to prevent certificate issues when accessing the proxy