fix collecting p2p/Peers metric (#1269)

cmd/statusd/main.go

@@ -139,8 +139,10 @@ func main() {
 		profiling.NewProfiler(*pprofPort).Go()
 	}
 
-	// Run stats server.
-	if *metrics {
+	// Start collecting metrics. Metrics can be enabled by providing `-metrics` flag
+	// or setting `gethmetrics.Enabled` to true during compilation time:
+	// https://github.com/status-im/go-ethereum/pull/76.
+	if *metrics || gethmetrics.Enabled {
 		go startCollectingNodeMetrics(interruptCh, backend.StatusNode())
 		go gethmetrics.CollectProcessMetrics(3 * time.Second)
 	}
@@ -202,8 +204,16 @@ func startCollectingNodeMetrics(interruptCh <-chan struct{}, statusNode *node.St
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	go func() {
+		// Try to subscribe and collect metrics. In case of an error, retry.
+		for {
 			if err := nodemetrics.SubscribeServerEvents(ctx, gethNode); err != nil {
 				logger.Error("Failed to subscribe server events", "error", err)
+			} else {
+				// no error means that the subscription was terminated by purpose
+				return
+			}
+
+			time.Sleep(time.Second)
 		}
 	}()
 

metrics/node/metrics.go

@@ -11,6 +11,7 @@ import (
 
 var (
 	nodePeersCounter  metrics.Counter
+	nodePeersGauge    metrics.Gauge
 	nodeMaxPeersGauge metrics.Gauge
 )
 
@@ -23,6 +24,7 @@ func init() {
 	}
 
 	nodePeersCounter = metrics.NewRegisteredCounter("p2p/Peers", nil)
+	nodePeersGauge = metrics.NewRegisteredGauge("p2p/PeersAbsolute", nil)
 	nodeMaxPeersGauge = metrics.NewRegisteredGauge("p2p/MaxPeers", nil)
 }
 
@@ -38,6 +40,7 @@ func updateNodeMetrics(node *node.Node, evType p2p.PeerEventType) error {
 		nodePeersCounter.Dec(1)
 	}
 
+	nodePeersGauge.Update(int64(server.PeerCount()))
 	nodeMaxPeersGauge.Update(int64(server.MaxPeers))
 
 	return nil

metrics/node/subscribe.go

@@ -23,6 +23,7 @@ func SubscribeServerEvents(ctx context.Context, node *node.Node) error {
 
 	ch := make(chan *p2p.PeerEvent, server.MaxPeers)
 	subscription := server.SubscribeEvents(ch)
+	defer subscription.Unsubscribe()
 
 	logger.Debug("Subscribed to server events")
 
@@ -38,10 +39,8 @@ func SubscribeServerEvents(ctx context.Context, node *node.Node) error {
 			if err != nil {
 				logger.Error("Subscription failed", "err", err)
 			}
-			subscription.Unsubscribe()
 			return err
 		case <-ctx.Done():
-			subscription.Unsubscribe()
 			return nil
 		}
 	}