From a00e7654b7fe842242352fb59b9c01b3f5e3c62d Mon Sep 17 00:00:00 2001
From: crn4 <vladimir.klementyev@gmail.com>
Date: Fri, 17 Oct 2025 16:06:53 +0200
Subject: [PATCH] simple balancing

---
 management/server/grpcserver.go | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/management/server/grpcserver.go b/management/server/grpcserver.go
index 12b59b691..29ccb3ae2 100644
--- a/management/server/grpcserver.go
+++ b/management/server/grpcserver.go
@@ -7,8 +7,10 @@ import (
 	"net"
 	"net/netip"
 	"os"
+	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	pb "github.com/golang/protobuf/proto" // nolint
@@ -44,6 +46,9 @@ import (
 const (
 	envLogBlockedPeers = "NB_LOG_BLOCKED_PEERS"
 	envBlockPeers      = "NB_BLOCK_SAME_PEERS"
+	envConcurrentSyncs = "NB_MAX_CONCURRENT_SYNCS"
+
+	defaultSyncLim = 1000
 )
 
 // GRPCServer an instance of a Management gRPC API server
@@ -63,6 +68,9 @@ type GRPCServer struct {
 	logBlockedPeers          bool
 	blockPeersWithSameConfig bool
 	integratedPeerValidator  integrated_validator.IntegratedValidator
+
+	syncSem atomic.Int32
+	syncLim int32
 }
 
 // NewServer creates a new Management server
@@ -96,6 +104,16 @@ func NewServer(
 	logBlockedPeers := strings.ToLower(os.Getenv(envLogBlockedPeers)) == "true"
 	blockPeersWithSameConfig := strings.ToLower(os.Getenv(envBlockPeers)) == "true"
 
+	syncLim := int32(defaultSyncLim)
+	if syncLimStr := os.Getenv(envConcurrentSyncs); syncLimStr != "" {
+		syncLimParsed, err := strconv.Atoi(syncLimStr)
+		if err != nil {
+			log.Errorf("invalid value for %s: %v using %d", envConcurrentSyncs, err, defaultSyncLim)
+		} else {
+			syncLim = int32(syncLimParsed)
+		}
+	}
+
 	return &GRPCServer{
 		wgKey: key,
 		// peerKey -> event channel
@@ -110,6 +128,8 @@ func NewServer(
 		logBlockedPeers:          logBlockedPeers,
 		blockPeersWithSameConfig: blockPeersWithSameConfig,
 		integratedPeerValidator:  integratedPeerValidator,
+
+		syncLim: syncLim,
 	}, nil
 }
 
@@ -151,6 +171,12 @@ func getRealIP(ctx context.Context) net.IP {
 // Sync validates the existence of a connecting peer, sends an initial state (all available for the connecting peers) and
 // notifies the connected peer of any updates (e.g. new peers under the same account)
 func (s *GRPCServer) Sync(req *proto.EncryptedMessage, srv proto.ManagementService_SyncServer) error {
+	if s.syncSem.Load() >= s.syncLim {
+		return status.Errorf(codes.ResourceExhausted, "too many concurrent sync requests, please try again later")
+	}
+	s.syncSem.Add(1)
+	defer s.syncSem.Add(-1)
+
 	reqStart := time.Now()
 
 	ctx := srv.Context()