lib: add flag to drop connection when running in cluster mode

Author: theanarkh

doc/api/net.md

@@ -599,12 +599,27 @@ changes:
 
 * {integer}
 
-Set this property to reject connections when the server's connection count gets
-high.
+When the number of connections reaches the threshold of `server.maxConnections`.
+
+1. Node.js will close the connection if the process is not running in cluster mode.
+2. Node.js will send the connection to other worker process by default if the process
+   is running in cluster mode, you can set `server.dropMaxConnection` to `true` to
+   close the connection.
 
 It is not recommended to use this option once a socket has been sent to a child
 with [`child_process.fork()`][].
 
+### `server.dropMaxConnection`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {boolean}
+
+Set this property to `true` to close the connection when the number of connections
+reaches the threshold of `server.maxConnections`. It only works in cluster mode.
+
 ### `server.ref()`
 
 <!-- YAML

lib/internal/cluster/child.js

@@ -233,7 +233,9 @@ function onconnection(message, handle) {
 
   if (accepted && server[owner_symbol]) {
     const self = server[owner_symbol];
-    if (self.maxConnections != null && self._connections >= self.maxConnections) {
+    if (self.maxConnections != null &&
+        self._connections >= self.maxConnections &&
+        !self.dropMaxConnection) {
       accepted = false;
     }
   }

test/parallel/test-net-server-drop-connections-in-cluster.js

@@ -0,0 +1,21 @@
+'use strict';
+const common = require('../common');
+const cluster = require('cluster');
+const http = require('http');
+
+if (cluster.isPrimary) {
+  cluster.fork();
+} else {
+  const server = http.createServer();
+  server.maxConnections = 0;
+  server.dropMaxConnection = true;
+  // When dropMaxConnection is false, the main process will continue to
+  // distribute the request to the child process, if true, the child will
+  // close the connection directly and emit drop event.
+  server.on('drop', common.mustCall((a) => {
+    process.exit();
+  }));
+  server.listen(common.mustCall(() => {
+    http.get(`http://localhost:${server.address().port}`).on('error', console.error);
+  }));
+}