Limit Client Connections (#828)

* expose connection limit option

* implement connection limit at handle new connection

* addressing comments

* fix unlimited connection limit

* release v1.0.45

Version.props

@@ -1,6 +1,6 @@
 <Project>
 	<!-- Versioning property for builds and packages -->
 	<PropertyGroup>
-		<VersionPrefix>1.0.44</VersionPrefix>
+		<VersionPrefix>1.0.45</VersionPrefix>
 	</PropertyGroup>
 </Project>

libs/host/Configuration/Options.cs

@@ -339,6 +339,10 @@ internal sealed class Options
         [Option("maxthreads", Required = false, HelpText = "Maximum worker and completion threads in thread pool, 0 uses the system default.")]
         public int ThreadPoolMaxThreads { get; set; }
 
+        [IntRangeValidation(-1, int.MaxValue)]
+        [Option("network-connection-limit", Required = false, Default = -1, HelpText = "Maximum number of simultaneously active network connections.")]
+        public int NetworkConnectionLimit { get; set; }
+
         [OptionValidation]
         [Option("use-azure-storage", Required = false, HelpText = "Use Azure Page Blobs for storage instead of local storage.")]
         public bool? UseAzureStorage { get; set; }
@@ -676,6 +680,7 @@ public GarnetServerOptions GetServerOptions(ILogger logger = null)
                 QuietMode = QuietMode.GetValueOrDefault(),
                 ThreadPoolMinThreads = ThreadPoolMinThreads,
                 ThreadPoolMaxThreads = ThreadPoolMaxThreads,
+                NetworkConnectionLimit = NetworkConnectionLimit,
                 DeviceFactoryCreator = useAzureStorage
                     ? () => new AzureStorageNamedDeviceFactory(AzureStorageConnectionString, logger)
                     : () => new LocalStorageNamedDeviceFactory(useNativeDeviceLinux: UseNativeDeviceLinux.GetValueOrDefault(), logger: logger),

libs/host/GarnetServer.cs

@@ -216,7 +216,7 @@ private void InitializeServer()
             }
 
             // Create Garnet TCP server if none was provided.
-            this.server ??= new GarnetServerTcp(opts.Address, opts.Port, 0, opts.TlsOptions, opts.NetworkSendThrottleMax, logger);
+            this.server ??= new GarnetServerTcp(opts.Address, opts.Port, 0, opts.TlsOptions, opts.NetworkSendThrottleMax, opts.NetworkConnectionLimit, logger);
 
             storeWrapper = new StoreWrapper(version, redisProtocolVersion, server, store, objectStore, objectStoreSizeTracker,
                     customCommandManager, appendOnlyFile, opts, clusterFactory: clusterFactory, loggerFactory: loggerFactory);

libs/host/defaults.conf

@@ -251,6 +251,9 @@
 	/* Maximum worker and completion threads in thread pool, 0 uses the system default. */
 	"ThreadPoolMaxThreads" : 0,
 
+	/* Maximum number of simultaneously active network connections. */
+	"NetworkConnectionLimit" : -1,
+
 	/* Use Azure Page Blobs for storage instead of local storage. */
 	"UseAzureStorage" : false,
 

libs/server/Servers/GarnetServerOptions.cs

@@ -246,6 +246,11 @@ public class GarnetServerOptions : ServerOptions
         /// </summary>
         public int ThreadPoolMaxThreads = 0;
 
+        /// <summary>
+        /// Maximum client connection limit
+        /// </summary>
+        public int NetworkConnectionLimit = -1;
+
         /// <summary>
         /// Creator of device factories
         /// </summary>

libs/server/Servers/GarnetServerTcp.cs

@@ -24,6 +24,7 @@ public class GarnetServerTcp : GarnetServerBase, IServerHook
         readonly int networkSendThrottleMax;
         readonly NetworkBufferSettings networkBufferSettings;
         readonly LimitedFixedBufferPool networkPool;
+        readonly int networkConnectionLimit;
 
         public IPEndPoint GetEndPoint
         {
@@ -69,9 +70,10 @@ public IEnumerable<IClusterSession> ActiveClusterSessions()
         /// <param name="tlsOptions"></param>
         /// <param name="networkSendThrottleMax"></param>
         /// <param name="logger"></param>
-        public GarnetServerTcp(string address, int port, int networkBufferSize = default, IGarnetTlsOptions tlsOptions = null, int networkSendThrottleMax = 8, ILogger logger = null)
+        public GarnetServerTcp(string address, int port, int networkBufferSize = default, IGarnetTlsOptions tlsOptions = null, int networkSendThrottleMax = 8, int networkConnectionLimit = -1, ILogger logger = null)
             : base(address, port, networkBufferSize, logger)
         {
+            this.networkConnectionLimit = networkConnectionLimit;
             this.tlsOptions = tlsOptions;
             this.networkSendThrottleMax = networkSendThrottleMax;
             var serverBufferSize = BufferSizeUtils.ServerBufferSize(new MaxSizeSettings());
@@ -134,11 +136,11 @@ private unsafe bool HandleNewConnection(SocketAsyncEventArgs e)
             string remoteEndpointName = e.AcceptSocket.RemoteEndPoint?.ToString();
             logger?.LogDebug("Accepted TCP connection from {remoteEndpoint}", remoteEndpointName);
 
-
             ServerTcpNetworkHandler handler = null;
             if (activeHandlerCount >= 0)
             {
-                if (Interlocked.Increment(ref activeHandlerCount) > 0)
+                var currentActiveHandlerCount = Interlocked.Increment(ref activeHandlerCount);
+                if (currentActiveHandlerCount > 0 && (networkConnectionLimit == -1 || currentActiveHandlerCount <= networkConnectionLimit))
                 {
                     try
                     {
@@ -157,6 +159,11 @@ private unsafe bool HandleNewConnection(SocketAsyncEventArgs e)
                         handler?.Dispose();
                     }
                 }
+                else
+                {
+                    Interlocked.Decrement(ref activeHandlerCount);
+                    e.AcceptSocket.Dispose();
+                }
             }
             return true;
         }