Add support for SO_REUSEPORT

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -407,6 +407,10 @@ public class VelocityConfiguration implements ProxyConfig {
     return forceKeyAuthentication;
   }
 
+  public boolean isEnableReusePort() {
+    return advanced.isEnableReusePort();
+  }
+
   @Override
   public String toString() {
     return MoreObjects.toStringHelper(this)
@@ -716,6 +720,8 @@ public class VelocityConfiguration implements ProxyConfig {
     private boolean logPlayerConnections = true;
     @Expose
     private boolean acceptTransfers = false;
+    @Expose
+    private boolean enableReusePort = false;
 
     private Advanced() {
     }
@@ -741,6 +747,7 @@ public class VelocityConfiguration implements ProxyConfig {
         this.logCommandExecutions = config.getOrElse("log-command-executions", false);
         this.logPlayerConnections = config.getOrElse("log-player-connections", true);
         this.acceptTransfers = config.getOrElse("accepts-transfers", false);
+        this.enableReusePort = config.getOrElse("enable-reuse-port", false);
       }
     }
 
@@ -804,6 +811,10 @@ public class VelocityConfiguration implements ProxyConfig {
       return this.acceptTransfers;
     }
 
+    public boolean isEnableReusePort() {
+      return enableReusePort;
+    }
+
     @Override
     public String toString() {
       return "Advanced{"
@@ -821,6 +832,7 @@ public class VelocityConfiguration implements ProxyConfig {
           + ", logCommandExecutions=" + logCommandExecutions
           + ", logPlayerConnections=" + logPlayerConnections
           + ", acceptTransfers=" + acceptTransfers
+          + ", enableReusePort=" + enableReusePort
           + '}';
     }
   }

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -18,6 +18,8 @@
 package com.velocitypowered.proxy.network;
 
 import com.google.common.base.Preconditions;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Multimap;
 import com.velocitypowered.api.event.proxy.ListenerBoundEvent;
 import com.velocitypowered.api.event.proxy.ListenerCloseEvent;
 import com.velocitypowered.api.network.ListenerType;
@@ -28,14 +30,17 @@ import com.velocitypowered.proxy.protocol.netty.GameSpyQueryHandler;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.bootstrap.ServerBootstrap;
 import io.netty.channel.Channel;
+import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelOption;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.WriteBufferWaterMark;
+import io.netty.channel.unix.UnixChannelOption;
 import io.netty.util.concurrent.GlobalEventExecutor;
+import io.netty.util.concurrent.MultithreadEventExecutorGroup;
 import java.net.InetSocketAddress;
 import java.net.http.HttpClient;
-import java.util.HashMap;
+import java.util.Collection;
 import java.util.Map;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -49,7 +54,7 @@ public final class ConnectionManager {
   private static final WriteBufferWaterMark SERVER_WRITE_MARK = new WriteBufferWaterMark(1 << 20,
       1 << 21);
   private static final Logger LOGGER = LogManager.getLogger(ConnectionManager.class);
-  private final Map<InetSocketAddress, Endpoint> endpoints = new HashMap<>();
+  private final Multimap<InetSocketAddress, Endpoint> endpoints = HashMultimap.create();
   private final TransportType transportType;
   private final EventLoopGroup bossGroup;
   private final EventLoopGroup workerGroup;
@@ -93,7 +98,6 @@ public final class ConnectionManager {
   public void bind(final InetSocketAddress address) {
     final ServerBootstrap bootstrap = new ServerBootstrap()
         .channelFactory(this.transportType.serverSocketChannelFactory)
-        .group(this.bossGroup, this.workerGroup)
         .childOption(ChannelOption.WRITE_BUFFER_WATER_MARK, SERVER_WRITE_MARK)
         .childHandler(this.serverChannelInitializer.get())
         .childOption(ChannelOption.TCP_NODELAY, true)
@@ -104,26 +108,50 @@ public final class ConnectionManager {
       bootstrap.option(ChannelOption.TCP_FASTOPEN, 3);
     }
 
-    bootstrap.bind()
+    if (server.getConfiguration().isEnableReusePort()) {
-        .addListener((ChannelFutureListener) future -> {
+      // We don't need a boss group, since each worker will bind to the socket
-          final Channel channel = future.channel();
+      bootstrap.option(UnixChannelOption.SO_REUSEPORT, true)
-          if (future.isSuccess()) {
+          .group(this.workerGroup);
-            this.endpoints.put(address, new Endpoint(channel, ListenerType.MINECRAFT));
+    } else {
-            
+      bootstrap.group(this.bossGroup, this.workerGroup);
-            // Warn people with console access that HAProxy is in use, see PR: #1436
+    }
-            if (this.server.getConfiguration().isProxyProtocol()) {
+
-              LOGGER.warn("Using HAProxy and listening on {}, please ensure this listener is adequately firewalled.", channel.localAddress());
+    final int binds = server.getConfiguration().isEnableReusePort()
+        ? ((MultithreadEventExecutorGroup) this.workerGroup).executorCount() : 1;
+
+    for (int bind = 0; bind < binds; bind++) {
+      // Wait for each bind to open. If we encounter any errors, don't try to bind again.
+      int finalBind = bind;
+      ChannelFuture f = bootstrap.bind()
+          .addListener((ChannelFutureListener) future -> {
+            final Channel channel = future.channel();
+            if (future.isSuccess()) {
+              this.endpoints.put(address, new Endpoint(channel, ListenerType.MINECRAFT));
+
+              LOGGER.info("Listening on {}", channel.localAddress());
+
+              if (finalBind == 0) {
+                // Warn people with console access that HAProxy is in use, see PR: #1436
+                if (this.server.getConfiguration().isProxyProtocol()) {
+                  LOGGER.warn(
+                      "Using HAProxy and listening on {}, please ensure this listener is adequately firewalled.",
+                      channel.localAddress());
+                }
+
+                // Fire the proxy bound event after the socket is bound
+                server.getEventManager().fireAndForget(
+                    new ListenerBoundEvent(address, ListenerType.MINECRAFT));
+              }
+            } else {
+              LOGGER.error("Can't bind to {}", address, future.cause());
             }
+          });
+      f.syncUninterruptibly();
 
-            LOGGER.info("Listening on {}", channel.localAddress());
+      if (!f.isSuccess()) {
-
+        break;
-            // Fire the proxy bound event after the socket is bound
+      }
-            server.getEventManager().fireAndForget(
+    }
-                new ListenerBoundEvent(address, ListenerType.MINECRAFT));
-          } else {
-            LOGGER.error("Can't bind to {}", address, future.cause());
-          }
-        });
   }
 
   /**
@@ -181,17 +209,20 @@ public final class ConnectionManager {
    * @param oldBind the endpoint to close
    */
   public void close(InetSocketAddress oldBind) {
-    Endpoint endpoint = endpoints.remove(oldBind);
+    Collection<Endpoint> endpoints = this.endpoints.removeAll(oldBind);
+    Preconditions.checkState(!endpoints.isEmpty(), "Endpoint was not registered");
+
+    ListenerType type = endpoints.iterator().next().getType();
 
     // Fire proxy close event to notify plugins of socket close. We block since plugins
     // should have a chance to be notified before the server stops accepting connections.
-    server.getEventManager().fire(new ListenerCloseEvent(oldBind, endpoint.getType())).join();
+    server.getEventManager().fire(new ListenerCloseEvent(oldBind, type)).join();
 
-    Channel serverChannel = endpoint.getChannel();
+    for (Endpoint endpoint : endpoints) {
-
+      Channel serverChannel = endpoint.getChannel();
-    Preconditions.checkState(serverChannel != null, "Endpoint %s not registered", oldBind);
+      LOGGER.info("Closing endpoint {}", serverChannel.localAddress());
-    LOGGER.info("Closing endpoint {}", serverChannel.localAddress());
+      serverChannel.close().syncUninterruptibly();
-    serverChannel.close().syncUninterruptibly();
+    }
   }
 
   /**
@@ -200,24 +231,28 @@ public final class ConnectionManager {
    * @param interrupt should closing forward interruptions
    */
   public void closeEndpoints(boolean interrupt) {
-    for (final Map.Entry<InetSocketAddress, Endpoint> entry : this.endpoints.entrySet()) {
+    for (final Map.Entry<InetSocketAddress, Collection<Endpoint>> entry : this.endpoints.asMap()
+        .entrySet()) {
       final InetSocketAddress address = entry.getKey();
-      final Endpoint endpoint = entry.getValue();
+      final Collection<Endpoint> endpoints = entry.getValue();
+      ListenerType type = endpoints.iterator().next().getType();
 
       // Fire proxy close event to notify plugins of socket close. We block since plugins
       // should have a chance to be notified before the server stops accepting connections.
-      server.getEventManager().fire(new ListenerCloseEvent(address, endpoint.getType())).join();
+      server.getEventManager().fire(new ListenerCloseEvent(address, type)).join();
 
-      LOGGER.info("Closing endpoint {}", address);
+      for (Endpoint endpoint : endpoints) {
-      if (interrupt) {
+        LOGGER.info("Closing endpoint {}", address);
-        try {
+        if (interrupt) {
-          endpoint.getChannel().close().sync();
+          try {
-        } catch (final InterruptedException e) {
+            endpoint.getChannel().close().sync();
-          LOGGER.info("Interrupted whilst closing endpoint", e);
+          } catch (final InterruptedException e) {
-          Thread.currentThread().interrupt();
+            LOGGER.info("Interrupted whilst closing endpoint", e);
+            Thread.currentThread().interrupt();
+          }
+        } else {
+          endpoint.getChannel().close().syncUninterruptibly();
         }
-      } else {
-        endpoint.getChannel().close().syncUninterruptibly();
       }
     }
     this.endpoints.clear();

proxy/src/main/resources/default-velocity.toml

@@ -145,6 +145,12 @@ log-player-connections = true
 # Transfer packet (Minecraft 1.20.5) to be received.
 accepts-transfers = false
 
+# Enables support for SO_REUSEPORT. This may help the proxy scale better on multicore systems
+# with a lot of incoming connections, and provide better CPU utilization than the existing
+# strategy of having a single thread accepting connections and distributing them to worker
+# threads. Disabled by default. Requires Linux or macOS.
+enable-reuse-port = false
+
 [query]
 # Whether to enable responding to GameSpy 4 query responses or not.
 enabled = false