network: fix MaxPeers, introduce AttemptConnPeers

Our node didn't respect the MaxPeers setting, fix it with a drop of random
connection when this limit is reached (to give a chance for newcomers to
communicate), but also introduce AttemptConnPeers setting to tune the number
of attempted connections.

This also raises the default MaxPeers for testnet/mainnet to 100, because
neo-go nodes love making friends.

config/config.go

@@ -72,6 +72,7 @@ type (
 		DialTimeout       time.Duration            `yaml:"DialTimeout"`
 		ProtoTickInterval time.Duration            `yaml:"ProtoTickInterval"`
 		MaxPeers          int                      `yaml:"MaxPeers"`
+		AttemptConnPeers  int                      `yaml:"AttemptConnPeers"`
 		MinPeers          int                      `yaml:"MinPeers"`
 		Monitoring        metrics.PrometheusConfig `yaml:"Monitoring"`
 		RPC               RPCConfig                `yaml:"RPC"`

config/protocol.mainnet.yml

@@ -46,7 +46,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 100
+  AttemptConnPeers: 20
   MinPeers: 5
   RPC:
     Enabled: true

config/protocol.privnet.docker.four.yml

@@ -34,7 +34,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 10
+  AttemptConnPeers: 5
   MinPeers: 3
   RPC:
     Enabled: true

config/protocol.privnet.docker.one.yml

@@ -31,7 +31,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 10
+  AttemptConnPeers: 5
   MinPeers: 3
   RPC:
     Enabled: true

config/protocol.privnet.docker.three.yml

@@ -31,7 +31,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 10
+  AttemptConnPeers: 5
   MinPeers: 3
   RPC:
     Enabled: true

config/protocol.privnet.docker.two.yml

@@ -31,7 +31,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 10
+  AttemptConnPeers: 5
   MinPeers: 3
   RPC:
     Enabled: true

config/protocol.privnet.yml

@@ -37,7 +37,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 10
+  AttemptConnPeers: 5
   MinPeers: 3
   RPC:
     Enabled: true

config/protocol.testnet.yml

@@ -46,7 +46,8 @@ ApplicationConfiguration:
   Relay: true
   DialTimeout: 3
   ProtoTickInterval: 2
-  MaxPeers: 50
+  MaxPeers: 100
+  AttemptConnPeers: 20
   MinPeers: 5
   RPC:
     Enabled: true

config/protocol.unit_testnet.yml

@@ -37,6 +37,7 @@ ApplicationConfiguration:
   DialTimeout: 3
   ProtoTickInterval: 2
   MaxPeers: 50
+  AttemptConnPeers: 5
   MinPeers: 1
   RPC:
     Enabled: true

pkg/network/server.go

@@ -18,11 +18,12 @@ import (
 
 const (
 	// peer numbers are arbitrary at the moment.
-	defaultMinPeers = 5
-	maxPeers        = 20
-	maxBlockBatch   = 200
-	maxAddrsToSend  = 200
-	minPoolCount    = 30
+	defaultMinPeers         = 5
+	defaultAttemptConnPeers = 20
+	defaultMaxPeers         = 100
+	maxBlockBatch           = 200
+	maxAddrsToSend          = 200
+	minPoolCount            = 30
 )
 
 var (
@@ -30,6 +31,7 @@ var (
 	errIdenticalID      = errors.New("identical node id")
 	errInvalidHandshake = errors.New("invalid handshake")
 	errInvalidNetwork   = errors.New("invalid network")
+	errMaxPeers         = errors.New("max peers reached")
 	errServerShutdown   = errors.New("server shutdown")
 	errInvalidInvType   = errors.New("invalid inventory type")
 )
@@ -86,6 +88,22 @@ func NewServer(config ServerConfig, chain core.Blockchainer) *Server {
 		s.MinPeers = defaultMinPeers
 	}
 
+	if s.MaxPeers <= 0 {
+		log.WithFields(log.Fields{
+			"MaxPeers configured": s.MaxPeers,
+			"MaxPeers actual":     defaultMaxPeers,
+		}).Info("bad MaxPeers configured, using the default value")
+		s.MaxPeers = defaultMaxPeers
+	}
+
+	if s.AttemptConnPeers <= 0 {
+		log.WithFields(log.Fields{
+			"AttemptConnPeers configured": s.AttemptConnPeers,
+			"AttemptConnPeers actual":     defaultAttemptConnPeers,
+		}).Info("bad AttemptConnPeers configured, using the default value")
+		s.AttemptConnPeers = defaultAttemptConnPeers
+	}
+
 	s.transport = NewTCPTransport(s, fmt.Sprintf(":%d", config.ListenTCP))
 	s.discovery = NewDefaultDiscovery(
 		s.DialTimeout,
@@ -137,9 +155,8 @@ func (s *Server) BadPeers() []string {
 
 func (s *Server) run() {
 	for {
-		c := s.PeerCount()
-		if c < s.ServerConfig.MinPeers {
-			s.discovery.RequestRemote(maxPeers - c)
+		if s.PeerCount() < s.MinPeers {
+			s.discovery.RequestRemote(s.AttemptConnPeers)
 		}
 		if s.discovery.PoolCount() < minPoolCount {
 			select {
@@ -170,6 +187,16 @@ func (s *Server) run() {
 			log.WithFields(log.Fields{
 				"addr": p.RemoteAddr(),
 			}).Info("new peer connected")
+			peerCount := s.PeerCount()
+			if peerCount > s.MaxPeers {
+				s.lock.RLock()
+				// Pick a random peer and drop connection to it.
+				for peer := range s.peers {
+					peer.Disconnect(errMaxPeers)
+					break
+				}
+				s.lock.RUnlock()
+			}
 			updatePeersConnectedMetric(s.PeerCount())
 
 		case drop := <-s.unregister:

pkg/network/server_config.go

@@ -15,6 +15,11 @@ type (
 		// connect with some new ones.
 		MinPeers int
 
+		// AttemptConnPeers it the number of connection to try to
+		// establish when the connection count drops below the MinPeers
+		// value.
+		AttemptConnPeers int
+
 		// MaxPeers it the maximum numbers of peers that can
 		// be connected to the server.
 		MaxPeers int
@@ -64,6 +69,7 @@ func NewServerConfig(cfg config.Config) ServerConfig {
 		DialTimeout:       appConfig.DialTimeout * time.Second,
 		ProtoTickInterval: appConfig.ProtoTickInterval * time.Second,
 		MaxPeers:          appConfig.MaxPeers,
+		AttemptConnPeers:  appConfig.AttemptConnPeers,
 		MinPeers:          appConfig.MinPeers,
 	}
 }