subpub: measure DHT latency and export via prometheus

subpub/discovery.go

@@ -10,13 +10,23 @@ import (
 	discrouting "github.com/libp2p/go-libp2p/p2p/discovery/routing"
 	discutil "github.com/libp2p/go-libp2p/p2p/discovery/util"
 	multiaddr "github.com/multiformats/go-multiaddr"
+	"github.com/prometheus/client_golang/prometheus"
 	"go.vocdoni.io/dvote/log"
+	"go.vocdoni.io/dvote/metrics"
+)
+
+// Metrics exported via prometheus
+var (
+	dhtLatency = prometheus.NewHistogram(prometheus.HistogramOpts{
+		Namespace: "file",
+		Name:      "peers_dht_latency",
+		Help:      "The time it takes FindPeers to discover peers",
+	})
 )
 
 // setupDiscovery creates a DHT discovery service and attaches it to the libp2p Host.
 // This lets us automatically discover peers and connect to them.
 func (s *SubPub) setupDiscovery(ctx context.Context) {
-
 	// Set a function as stream handler. This function is called when a peer
 	// initiates a connection and starts a stream with this peer.
 	if !s.OnlyDiscover {
@@ -29,6 +39,8 @@ func (s *SubPub) setupDiscovery(ctx context.Context) {
 	s.routing = discrouting.NewRoutingDiscovery(s.node.DHT)
 	discutil.Advertise(ctx, s.routing, s.Topic)
 
+	metrics.Register(dhtLatency)
+
 	// Discover new peers periodically
 	go func() { // this spawns a single background task per instance
 		for {
@@ -46,6 +58,7 @@ func (s *SubPub) setupDiscovery(ctx context.Context) {
 }
 
 func (s *SubPub) discover(ctx context.Context) {
+	dhtLatencyTimer := prometheus.NewTimer(dhtLatency)
 	// Now, look for others who have announced.
 	// This is like your friend telling you the location to meet you.
 	log.Debugf("looking for peers in topic %s", s.Topic)
@@ -69,6 +82,8 @@ func (s *SubPub) discover(ctx context.Context) {
 			continue
 		}
 		// new peer; let's connect to it
+		// first update the latency metrics
+		dhtLatencyTimer.ObserveDuration()
 		connectCtx, cancel := context.WithTimeout(ctx, time.Second*10)
 		if err := s.node.PeerHost.Connect(connectCtx, peer); err != nil {
 			cancel()