Merge pull request #2885 from cfromknecht/stagger-initial-reconnect

server: stagger initial reconnects

config.go

@@ -256,6 +256,8 @@ type config struct {
 
 	RejectPush bool `long:"rejectpush" description:"If true, lnd will not accept channel opening requests with non-zero push amounts. This should prevent accidental pushes to merchant nodes."`
 
+	StaggerInitialReconnect bool `long:"stagger-initial-reconnect" description:"If true, will apply a randomized staggering between 0s and 30s when reconnecting to persistent peers on startup. The first 10 reconnections will be attempted instantly, regardless of the flag's value"`
+
 	net tor.Net
 
 	Routing *routing.Conf `group:"routing" namespace:"routing"`

server.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"image/color"
 	"math/big"
+	prand "math/rand"
 	"net"
 	"path/filepath"
 	"regexp"
@@ -60,6 +61,18 @@ const (
 	// durations exceeding this value will be eligible to have their
 	// backoffs reduced.
 	defaultStableConnDuration = 10 * time.Minute
+
+	// numInstantInitReconnect specifies how many persistent peers we should
+	// always attempt outbound connections to immediately. After this value
+	// is surpassed, the remaining peers will be randomly delayed using
+	// maxInitReconnectDelay.
+	numInstantInitReconnect = 10
+
+	// maxInitReconnectDelay specifies the maximum delay in seconds we will
+	// apply in attempting to reconnect to persistent peers on startup. The
+	// value used or a particular peer will be chosen between 0s and this
+	// value.
+	maxInitReconnectDelay = 30
 )
 
 var (
@@ -1932,6 +1945,7 @@ func (s *server) establishPersistentConnections() error {
 
 	// Iterate through the combined list of addresses from prior links and
 	// node announcements and attempt to reconnect to each node.
+	var numOutboundConns int
 	for pubStr, nodeAddr := range nodeAddrsMap {
 		// Add this peer to the set of peers we should maintain a
 		// persistent connection with.
@@ -1962,13 +1976,42 @@ func (s *server) establishPersistentConnections() error {
 			s.persistentConnReqs[pubStr] = append(
 				s.persistentConnReqs[pubStr], connReq)
 
+			// We'll connect to the first 10 peers immediately, then
+			// randomly stagger any remaining connections if the
+			// stagger initial reconnect flag is set. This ensures
+			// that mobile nodes or nodes with a small number of
+			// channels obtain connectivity quickly, but larger
+			// nodes are able to disperse the costs of connecting to
+			// all peers at once.
+			if numOutboundConns < numInstantInitReconnect ||
+				!cfg.StaggerInitialReconnect {
+
 				go s.connMgr.Connect(connReq)
+			} else {
+				go s.delayInitialReconnect(connReq)
 			}
 		}
 
+		numOutboundConns++
+	}
+
 	return nil
 }
 
+// delayInitialReconnect will attempt a reconnection using the passed connreq
+// after sampling a value for the delay between 0s and the
+// maxInitReconnectDelay.
+//
+// NOTE: This method MUST be run as a goroutine.
+func (s *server) delayInitialReconnect(connReq *connmgr.ConnReq) {
+	delay := time.Duration(prand.Intn(maxInitReconnectDelay)) * time.Second
+	select {
+	case <-time.After(delay):
+		s.connMgr.Connect(connReq)
+	case <-s.quit:
+	}
+}
+
 // prunePersistentPeerConnection removes all internal state related to
 // persistent connections to a peer within the server. This is used to avoid
 // persistent connection retries to peers we do not have any open channels with.