cmd/geth: allow configuring metrics HTTP server on separate endpoint (#21290)

Exposing /debug/metrics and /debug/metrics/prometheus was dependent
on --pprof, which also exposes other HTTP APIs. This change makes it possible
to run the metrics server on an independent endpoint without enabling pprof.

cmd/geth/chaincmd.go

@@ -85,6 +85,8 @@ The dumpgenesis command dumps the genesis block configuration in JSON format to
 			utils.CacheGCFlag,
 			utils.MetricsEnabledFlag,
 			utils.MetricsEnabledExpensiveFlag,
+			utils.MetricsHTTPFlag,
+			utils.MetricsPortFlag,
 			utils.MetricsEnableInfluxDBFlag,
 			utils.MetricsInfluxDBEndpointFlag,
 			utils.MetricsInfluxDBDatabaseFlag,

cmd/geth/main.go

@@ -199,6 +199,8 @@ var (
 	metricsFlags = []cli.Flag{
 		utils.MetricsEnabledFlag,
 		utils.MetricsEnabledExpensiveFlag,
+		utils.MetricsHTTPFlag,
+		utils.MetricsPortFlag,
 		utils.MetricsEnableInfluxDBFlag,
 		utils.MetricsInfluxDBEndpointFlag,
 		utils.MetricsInfluxDBDatabaseFlag,

cmd/utils/flags.go

@@ -51,6 +51,7 @@ import (
 	"github.com/ethereum/go-ethereum/les"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
+	"github.com/ethereum/go-ethereum/metrics/exp"
 	"github.com/ethereum/go-ethereum/metrics/influxdb"
 	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/node"
@@ -689,6 +690,21 @@ var (
 		Name:  "metrics.expensive",
 		Usage: "Enable expensive metrics collection and reporting",
 	}
+
+	// MetricsHTTPFlag defines the endpoint for a stand-alone metrics HTTP endpoint.
+	// Since the pprof service enables sensitive/vulnerable behavior, this allows a user
+	// to enable a public-OK metrics endpoint without having to worry about ALSO exposing
+	// other profiling behavior or information.
+	MetricsHTTPFlag = cli.StringFlag{
+		Name:  "metrics.addr",
+		Usage: "Enable stand-alone metrics HTTP server listening interface",
+		Value: "127.0.0.1",
+	}
+	MetricsPortFlag = cli.IntFlag{
+		Name:  "metrics.port",
+		Usage: "Metrics HTTP server listening port",
+		Value: 6060,
+	}
 	MetricsEnableInfluxDBFlag = cli.BoolFlag{
 		Name:  "metrics.influxdb",
 		Usage: "Enable metrics export/push to an external InfluxDB database",
@@ -1734,6 +1750,7 @@ func RegisterGraphQLService(stack *node.Node, endpoint string, cors, vhosts []st
 func SetupMetrics(ctx *cli.Context) {
 	if metrics.Enabled {
 		log.Info("Enabling metrics collection")
+
 		var (
 			enableExport = ctx.GlobalBool(MetricsEnableInfluxDBFlag.Name)
 			endpoint     = ctx.GlobalString(MetricsInfluxDBEndpointFlag.Name)
@@ -1749,6 +1766,12 @@ func SetupMetrics(ctx *cli.Context) {
 
 			go influxdb.InfluxDBWithTags(metrics.DefaultRegistry, 10*time.Second, endpoint, database, username, password, "geth.", tagsMap)
 		}
+
+		if ctx.GlobalIsSet(MetricsHTTPFlag.Name) {
+			address := fmt.Sprintf("%s:%d", ctx.GlobalString(MetricsHTTPFlag.Name), ctx.GlobalInt(MetricsPortFlag.Name))
+			log.Info("Enabling stand-alone metrics HTTP endpoint", "address", address)
+			exp.Setup(address)
+		}
 	}
 }
 

internal/debug/flags.go

@@ -195,15 +195,19 @@ func Setup(ctx *cli.Context) error {
 		}
 
 		address := fmt.Sprintf("%s:%d", listenHost, port)
-		StartPProf(address)
+		// This context value ("metrics.addr") represents the utils.MetricsHTTPFlag.Name.
+		// It cannot be imported because it will cause a cyclical dependency.
+		StartPProf(address, !ctx.GlobalIsSet("metrics.addr"))
 	}
 	return nil
 }
 
-func StartPProf(address string) {
+func StartPProf(address string, withMetrics bool) {
 	// Hook go-metrics into expvar on any /debug/metrics request, load all vars
 	// from the registry into expvar, and execute regular expvar handler.
+	if withMetrics {
 		exp.Exp(metrics.DefaultRegistry)
+	}
 	http.Handle("/memsize/", http.StripPrefix("/memsize", &Memsize))
 	log.Info("Starting pprof server", "addr", fmt.Sprintf("http://%s/debug/pprof", address))
 	go func() {

metrics/exp/exp.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"sync"
 
+	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/metrics/prometheus"
 )
@@ -52,6 +53,20 @@ func ExpHandler(r metrics.Registry) http.Handler {
 	return http.HandlerFunc(e.expHandler)
 }
 
+// Setup starts a dedicated metrics server at the given address.
+// This function enables metrics reporting separate from pprof.
+func Setup(address string) {
+	m := http.NewServeMux()
+	m.Handle("/debug/metrics", ExpHandler(metrics.DefaultRegistry))
+	m.Handle("/debug/metrics/prometheus", prometheus.Handler(metrics.DefaultRegistry))
+	log.Info("Starting metrics server", "addr", fmt.Sprintf("http://%s/debug/metrics", address))
+	go func() {
+		if err := http.ListenAndServe(address, m); err != nil {
+			log.Error("Failure in running metrics server", "err", err)
+		}
+	}()
+}
+
 func (exp *exp) getInt(name string) *expvar.Int {
 	var v *expvar.Int
 	exp.expvarLock.Lock()

mobile/geth.go

@@ -113,7 +113,7 @@ func NewNode(datadir string, config *NodeConfig) (stack *Node, _ error) {
 	}
 
 	if config.PprofAddress != "" {
-		debug.StartPProf(config.PprofAddress)
+		debug.StartPProf(config.PprofAddress, true)
 	}
 
 	// Create the empty networking stack