Restrict Dials From Discovery (#14052)

* Fix Excessive Subnet Dials

* Handle backoff in Iterator

* Slow Down Lookups

* Add Flag To Configure Dials

* Preston's Review

* Update cmd/beacon-chain/flags/base.go

Co-authored-by: Preston Van Loon <[email protected]>

* Reduce polling period

* Manu's Review

---------

Co-authored-by: Preston Van Loon <[email protected]>

beacon-chain/p2p/discovery.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"crypto/ecdsa"
 	"net"
+	"sync"
 	"time"
 
 	"github.com/ethereum/go-ethereum/p2p/discover"
@@ -15,6 +16,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/go-bitfield"
 	"github.com/prysmaticlabs/prysm/v5/beacon-chain/cache"
+	"github.com/prysmaticlabs/prysm/v5/cmd/beacon-chain/flags"
 	"github.com/prysmaticlabs/prysm/v5/config/features"
 	"github.com/prysmaticlabs/prysm/v5/config/params"
 	ecdsaprysm "github.com/prysmaticlabs/prysm/v5/crypto/ecdsa"
@@ -106,7 +108,7 @@ func (s *Service) RefreshENR() {
 
 // listen for new nodes watches for new nodes in the network and adds them to the peerstore.
 func (s *Service) listenForNewNodes() {
-	iterator := enode.Filter(s.dv5Listener.RandomNodes(), s.filterPeer)
+	iterator := filterNodes(s.ctx, s.dv5Listener.RandomNodes(), s.filterPeer)
 	defer iterator.Close()
 
 	for {
@@ -122,29 +124,41 @@ func (s *Service) listenForNewNodes() {
 			time.Sleep(pollingPeriod)
 			continue
 		}
-
-		if exists := iterator.Next(); !exists {
-			break
-		}
-
-		node := iterator.Node()
-		peerInfo, _, err := convertToAddrInfo(node)
-		if err != nil {
-			log.WithError(err).Error("Could not convert to peer info")
+		wantedCount := s.wantedPeerDials()
+		if wantedCount == 0 {
+			log.Trace("Not looking for peers, at peer limit")
+			time.Sleep(pollingPeriod)
 			continue
 		}
-
-		if peerInfo == nil {
-			continue
+		// Restrict dials if limit is applied.
+		if flags.MaxDialIsActive() {
+			wantedCount = min(wantedCount, flags.Get().MaxConcurrentDials)
 		}
+		wantedNodes := enode.ReadNodes(iterator, wantedCount)
+		wg := new(sync.WaitGroup)
+		for i := 0; i < len(wantedNodes); i++ {
+			node := wantedNodes[i]
+			peerInfo, _, err := convertToAddrInfo(node)
+			if err != nil {
+				log.WithError(err).Error("Could not convert to peer info")
+				continue
+			}
 
-		// Make sure that peer is not dialed too often, for each connection attempt there's a backoff period.
-		s.Peers().RandomizeBackOff(peerInfo.ID)
-		go func(info *peer.AddrInfo) {
-			if err := s.connectWithPeer(s.ctx, *info); err != nil {
-				log.WithError(err).Tracef("Could not connect with peer %s", info.String())
+			if peerInfo == nil {
+				continue
 			}
-		}(peerInfo)
+
+			// Make sure that peer is not dialed too often, for each connection attempt there's a backoff period.
+			s.Peers().RandomizeBackOff(peerInfo.ID)
+			wg.Add(1)
+			go func(info *peer.AddrInfo) {
+				if err := s.connectWithPeer(s.ctx, *info); err != nil {
+					log.WithError(err).Tracef("Could not connect with peer %s", info.String())
+				}
+				wg.Done()
+			}(peerInfo)
+		}
+		wg.Wait()
 	}
 }
 
@@ -384,6 +398,17 @@ func (s *Service) isPeerAtLimit(inbound bool) bool {
 	return activePeers >= maxPeers || numOfConns >= maxPeers
 }
 
+func (s *Service) wantedPeerDials() int {
+	maxPeers := int(s.cfg.MaxPeers)
+
+	activePeers := len(s.Peers().Active())
+	wantedCount := 0
+	if maxPeers > activePeers {
+		wantedCount = maxPeers - activePeers
+	}
+	return wantedCount
+}
+
 // PeersFromStringAddrs converts peer raw ENRs into multiaddrs for p2p.
 func PeersFromStringAddrs(addrs []string) ([]ma.Multiaddr, error) {
 	var allAddrs []ma.Multiaddr

beacon-chain/p2p/iterator.go

@@ -2,10 +2,14 @@ package p2p
 
 import (
 	"context"
+	"runtime"
+	"time"
 
 	"github.com/ethereum/go-ethereum/p2p/enode"
 )
 
+const backOffCounter = 50
+
 // filterNodes wraps an iterator such that Next only returns nodes for which
 // the 'check' function returns true. This custom implementation also
 // checks for context deadlines so that in the event the parent context has
@@ -24,13 +28,21 @@ type filterIter struct {
 // Next looks up for the next valid node according to our
 // filter criteria.
 func (f *filterIter) Next() bool {
+	lookupCounter := 0
 	for f.Iterator.Next() {
+		// Do not excessively perform lookups if we constantly receive non-viable peers.
+		if lookupCounter > backOffCounter {
+			lookupCounter = 0
+			runtime.Gosched()
+			time.Sleep(pollingPeriod)
+		}
 		if f.Context.Err() != nil {
 			return false
 		}
 		if f.check(f.Node()) {
 			return true
 		}
+		lookupCounter++
 	}
 	return false
 }

beacon-chain/p2p/subnets.go

@@ -87,7 +87,12 @@ func (s *Service) FindPeersWithSubnet(ctx context.Context, topic string,
 			return false, errors.Errorf("unable to find requisite number of peers for topic %s - "+
 				"only %d out of %d peers were able to be found", topic, currNum, threshold)
 		}
-		nodes := enode.ReadNodes(iterator, int(params.BeaconNetworkConfig().MinimumPeersInSubnetSearch))
+		nodeCount := int(params.BeaconNetworkConfig().MinimumPeersInSubnetSearch)
+		// Restrict dials if limit is applied.
+		if flags.MaxDialIsActive() {
+			nodeCount = min(nodeCount, flags.Get().MaxConcurrentDials)
+		}
+		nodes := enode.ReadNodes(iterator, nodeCount)
 		for _, node := range nodes {
 			info, _, err := convertToAddrInfo(node)
 			if err != nil {

cmd/beacon-chain/flags/base.go

@@ -227,6 +227,12 @@ var (
 		Usage: "Sets the minimum number of peers that a node will attempt to peer with that are subscribed to a subnet.",
 		Value: 6,
 	}
+	// MaxConcurrentDials defines a flag to set the maximum number of peers that a node will attempt to dial with from discovery.
+	MaxConcurrentDials = &cli.Uint64Flag{
+		Name: "max-concurrent-dials",
+		Usage: "Sets the maximum number of peers that a node will attempt to dial with from discovery. By default we will dials as " +
+			"many peers as possible.",
+	}
 	// SuggestedFeeRecipient specifies the fee recipient for the transaction fees.
 	SuggestedFeeRecipient = &cli.StringFlag{
 		Name:  "suggested-fee-recipient",

cmd/beacon-chain/flags/config.go

@@ -11,6 +11,7 @@ type GlobalFlags struct {
 	SubscribeToAllSubnets      bool
 	MinimumSyncPeers           int
 	MinimumPeersPerSubnet      int
+	MaxConcurrentDials         int
 	BlockBatchLimit            int
 	BlockBatchLimitBurstFactor int
 	BlobBatchLimit             int
@@ -45,11 +46,17 @@ func ConfigureGlobalFlags(ctx *cli.Context) {
 	cfg.BlobBatchLimit = ctx.Int(BlobBatchLimit.Name)
 	cfg.BlobBatchLimitBurstFactor = ctx.Int(BlobBatchLimitBurstFactor.Name)
 	cfg.MinimumPeersPerSubnet = ctx.Int(MinPeersPerSubnet.Name)
+	cfg.MaxConcurrentDials = ctx.Int(MaxConcurrentDials.Name)
 	configureMinimumPeers(ctx, cfg)
 
 	Init(cfg)
 }
 
+// MaxDialIsActive checks if the user has enabled the max dial flag.
+func MaxDialIsActive() bool {
+	return Get().MaxConcurrentDials > 0
+}
+
 func configureMinimumPeers(ctx *cli.Context, cfg *GlobalFlags) {
 	cfg.MinimumSyncPeers = ctx.Int(MinSyncPeers.Name)
 	maxPeers := ctx.Int(cmd.P2PMaxPeers.Name)

cmd/beacon-chain/main.go

@@ -72,6 +72,7 @@ var appFlags = []cli.Flag{
 	flags.WeakSubjectivityCheckpoint,
 	flags.Eth1HeaderReqLimit,
 	flags.MinPeersPerSubnet,
+	flags.MaxConcurrentDials,
 	flags.SuggestedFeeRecipient,
 	flags.TerminalTotalDifficultyOverride,
 	flags.TerminalBlockHashOverride,

cmd/beacon-chain/usage.go

@@ -124,6 +124,7 @@ var appHelpFlagGroups = []flagGroup{
 			flags.WeakSubjectivityCheckpoint,
 			flags.Eth1HeaderReqLimit,
 			flags.MinPeersPerSubnet,
+			flags.MaxConcurrentDials,
 			flags.MevRelayEndpoint,
 			flags.MaxBuilderEpochMissedSlots,
 			flags.MaxBuilderConsecutiveMissedSlots,