1<!DOCTYPE html> 2<html lang="en"> 3<head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <meta name="nodejs.org:node-version" content="v18.20.1"> 7 <title>Cluster | Node.js v18.20.1 Documentation</title> 8 <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> 9 <link rel="stylesheet" href="assets/style.css"> 10 <link rel="stylesheet" href="assets/hljs.css"> 11 <link rel="canonical" href="https://nodejs.org/api/cluster.html"> 12 <script async defer src="assets/api.js" type="text/javascript"></script> 13 <style>@media(max-width:542px){.with-40-chars>.js-flavor-selector{float:none;margin:0 0 1em auto;}}@media(max-width:582px){.with-45-chars>.js-flavor-selector{float:none;margin:0 0 1em auto;}}</style> 14</head> 15<body class="alt apidoc" id="api-section-cluster"> 16 <div id="content" class="clearfix"> 17 <div id="column2" class="interior"> 18 <div id="intro" class="interior"> 19 <a href="/" 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<code>'online'</code></a></li> 134<li><a href="#workerdisconnect"><code>worker.disconnect()</code></a></li> 135<li><a href="#workerexitedafterdisconnect"><code>worker.exitedAfterDisconnect</code></a></li> 136<li><a href="#workerid"><code>worker.id</code></a></li> 137<li><a href="#workerisconnected"><code>worker.isConnected()</code></a></li> 138<li><a href="#workerisdead"><code>worker.isDead()</code></a></li> 139<li><a href="#workerkillsignal"><code>worker.kill([signal])</code></a></li> 140<li><a href="#workerprocess"><code>worker.process</code></a></li> 141<li><a href="#workersendmessage-sendhandle-options-callback"><code>worker.send(message[, sendHandle[, options]][, callback])</code></a></li> 142</ul> 143</li> 144<li><a href="#event-disconnect_1">Event: <code>'disconnect'</code></a></li> 145<li><a href="#event-exit_1">Event: <code>'exit'</code></a></li> 146<li><a href="#event-fork">Event: <code>'fork'</code></a></li> 147<li><a href="#event-listening_1">Event: <code>'listening'</code></a></li> 148<li><a href="#event-message_1">Event: <code>'message'</code></a></li> 149<li><a href="#event-online_1">Event: <code>'online'</code></a></li> 150<li><a href="#event-setup">Event: <code>'setup'</code></a></li> 151<li><a href="#clusterdisconnectcallback"><code>cluster.disconnect([callback])</code></a></li> 152<li><a href="#clusterforkenv"><code>cluster.fork([env])</code></a></li> 153<li><span class="stability_0"><a href="#clusterismaster"><code>cluster.isMaster</code></a></span></li> 154<li><a href="#clusterisprimary"><code>cluster.isPrimary</code></a></li> 155<li><a href="#clusterisworker"><code>cluster.isWorker</code></a></li> 156<li><a href="#clusterschedulingpolicy"><code>cluster.schedulingPolicy</code></a></li> 157<li><a href="#clustersettings"><code>cluster.settings</code></a></li> 158<li><span class="stability_0"><a href="#clustersetupmastersettings"><code>cluster.setupMaster([settings])</code></a></span></li> 159<li><a href="#clustersetupprimarysettings"><code>cluster.setupPrimary([settings])</code></a></li> 160<li><a href="#clusterworker"><code>cluster.worker</code></a></li> 161<li><a href="#clusterworkers"><code>cluster.workers</code></a></li> 162</ul> 163</li> 164</ul></div></div> 165 </li> 166 167 168 <li class="picker-header"> 169 <a href="#"> 170 <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 171 Index 172 </a> 173 174 <div class="picker"><ul> 175<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 176<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 177 178 <li> 179 <a href="index.html">Index</a> 180 </li> 181 </ul> 182 183<hr class="line"> 184<ul> 185<li><a href="assert.html" class="nav-assert">Assertion testing</a></li> 186<li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> 187<li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> 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href="zlib.html" class="nav-zlib">Zlib</a></li> 245</ul> 246<hr class="line"> 247<ul> 248<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> 249</ul></div> 250 </li> 251 252 253 <li class="picker-header"> 254 <a href="#"> 255 <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 256 Other versions 257 </a> 258 <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v21.x/api/cluster.html">21.x</a></li> 259<li><a href="https://nodejs.org/docs/latest-v20.x/api/cluster.html">20.x <b>LTS</b></a></li> 260<li><a href="https://nodejs.org/docs/latest-v19.x/api/cluster.html">19.x</a></li> 261<li><a href="https://nodejs.org/docs/latest-v18.x/api/cluster.html">18.x <b>LTS</b></a></li> 262<li><a href="https://nodejs.org/docs/latest-v17.x/api/cluster.html">17.x</a></li> 263<li><a href="https://nodejs.org/docs/latest-v16.x/api/cluster.html">16.x</a></li> 264<li><a href="https://nodejs.org/docs/latest-v15.x/api/cluster.html">15.x</a></li> 265<li><a href="https://nodejs.org/docs/latest-v14.x/api/cluster.html">14.x</a></li> 266<li><a href="https://nodejs.org/docs/latest-v13.x/api/cluster.html">13.x</a></li> 267<li><a href="https://nodejs.org/docs/latest-v12.x/api/cluster.html">12.x</a></li> 268<li><a href="https://nodejs.org/docs/latest-v11.x/api/cluster.html">11.x</a></li> 269<li><a href="https://nodejs.org/docs/latest-v10.x/api/cluster.html">10.x</a></li> 270<li><a href="https://nodejs.org/docs/latest-v9.x/api/cluster.html">9.x</a></li> 271<li><a href="https://nodejs.org/docs/latest-v8.x/api/cluster.html">8.x</a></li> 272<li><a href="https://nodejs.org/docs/latest-v7.x/api/cluster.html">7.x</a></li> 273<li><a href="https://nodejs.org/docs/latest-v6.x/api/cluster.html">6.x</a></li> 274<li><a href="https://nodejs.org/docs/latest-v5.x/api/cluster.html">5.x</a></li> 275<li><a href="https://nodejs.org/docs/latest-v4.x/api/cluster.html">4.x</a></li> 276<li><a href="https://nodejs.org/docs/latest-v0.12.x/api/cluster.html">0.12.x</a></li> 277<li><a href="https://nodejs.org/docs/latest-v0.10.x/api/cluster.html">0.10.x</a></li></ol></div> 278 </li> 279 280 <li class="picker-header"> 281 <a href="#"> 282 <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 283 Options 284 </a> 285 286 <div class="picker"> 287 <ul> 288 <li> 289 <a href="all.html">View on single page</a> 290 </li> 291 <li> 292 <a href="cluster.json">View as JSON</a> 293 </li> 294 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/cluster.md">Edit on GitHub</a></li> 295 </ul> 296 </div> 297 </li> 298 </ul> 299 </div> 300 <hr> 301 </header> 302 303 <details id="toc" open><summary>Table of contents</summary><ul> 304<li><span class="stability_2"><a href="#cluster">Cluster</a></span> 305<ul> 306<li><a href="#how-it-works">How it works</a></li> 307<li><a href="#class-worker">Class: <code>Worker</code></a> 308<ul> 309<li><a href="#event-disconnect">Event: <code>'disconnect'</code></a></li> 310<li><a href="#event-error">Event: <code>'error'</code></a></li> 311<li><a href="#event-exit">Event: <code>'exit'</code></a></li> 312<li><a href="#event-listening">Event: <code>'listening'</code></a></li> 313<li><a href="#event-message">Event: <code>'message'</code></a></li> 314<li><a href="#event-online">Event: <code>'online'</code></a></li> 315<li><a href="#workerdisconnect"><code>worker.disconnect()</code></a></li> 316<li><a href="#workerexitedafterdisconnect"><code>worker.exitedAfterDisconnect</code></a></li> 317<li><a href="#workerid"><code>worker.id</code></a></li> 318<li><a href="#workerisconnected"><code>worker.isConnected()</code></a></li> 319<li><a href="#workerisdead"><code>worker.isDead()</code></a></li> 320<li><a href="#workerkillsignal"><code>worker.kill([signal])</code></a></li> 321<li><a href="#workerprocess"><code>worker.process</code></a></li> 322<li><a href="#workersendmessage-sendhandle-options-callback"><code>worker.send(message[, sendHandle[, options]][, callback])</code></a></li> 323</ul> 324</li> 325<li><a href="#event-disconnect_1">Event: <code>'disconnect'</code></a></li> 326<li><a href="#event-exit_1">Event: <code>'exit'</code></a></li> 327<li><a href="#event-fork">Event: <code>'fork'</code></a></li> 328<li><a href="#event-listening_1">Event: <code>'listening'</code></a></li> 329<li><a href="#event-message_1">Event: <code>'message'</code></a></li> 330<li><a href="#event-online_1">Event: <code>'online'</code></a></li> 331<li><a href="#event-setup">Event: <code>'setup'</code></a></li> 332<li><a href="#clusterdisconnectcallback"><code>cluster.disconnect([callback])</code></a></li> 333<li><a href="#clusterforkenv"><code>cluster.fork([env])</code></a></li> 334<li><span class="stability_0"><a href="#clusterismaster"><code>cluster.isMaster</code></a></span></li> 335<li><a href="#clusterisprimary"><code>cluster.isPrimary</code></a></li> 336<li><a href="#clusterisworker"><code>cluster.isWorker</code></a></li> 337<li><a href="#clusterschedulingpolicy"><code>cluster.schedulingPolicy</code></a></li> 338<li><a href="#clustersettings"><code>cluster.settings</code></a></li> 339<li><span class="stability_0"><a href="#clustersetupmastersettings"><code>cluster.setupMaster([settings])</code></a></span></li> 340<li><a href="#clustersetupprimarysettings"><code>cluster.setupPrimary([settings])</code></a></li> 341<li><a href="#clusterworker"><code>cluster.worker</code></a></li> 342<li><a href="#clusterworkers"><code>cluster.workers</code></a></li> 343</ul> 344</li> 345</ul></details> 346 347 <div id="apicontent"> 348 <h2>Cluster<span><a class="mark" href="#cluster" id="cluster">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster"></a></h2> 349 350<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p> 351<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/cluster.js">lib/cluster.js</a></p> 352<p>Clusters of Node.js processes can be used to run multiple instances of Node.js 353that can distribute workloads among their application threads. When process 354isolation is not needed, use the <a href="worker_threads.html"><code>worker_threads</code></a> module instead, which 355allows running multiple application threads within a single Node.js instance.</p> 356<p>The cluster module allows easy creation of child processes that all share 357server ports.</p> 358 359<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 360<span class="hljs-keyword">import</span> http <span class="hljs-keyword">from</span> <span class="hljs-string">'node:http'</span>; 361<span class="hljs-keyword">import</span> { availableParallelism } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:os'</span>; 362<span class="hljs-keyword">import</span> process <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 363 364<span class="hljs-keyword">const</span> numCPUs = <span class="hljs-title function_">availableParallelism</span>(); 365 366<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 367 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Primary <span class="hljs-subst">${process.pid}</span> is running`</span>); 368 369 <span class="hljs-comment">// Fork workers.</span> 370 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 371 cluster.<span class="hljs-title function_">fork</span>(); 372 } 373 374 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 375 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker <span class="hljs-subst">${worker.process.pid}</span> died`</span>); 376 }); 377} <span class="hljs-keyword">else</span> { 378 <span class="hljs-comment">// Workers can share any TCP connection</span> 379 <span class="hljs-comment">// In this case it is an HTTP server</span> 380 http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 381 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 382 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'hello world\n'</span>); 383 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 384 385 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Worker <span class="hljs-subst">${process.pid}</span> started`</span>); 386}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 387<span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 388<span class="hljs-keyword">const</span> numCPUs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:os'</span>).<span class="hljs-title function_">availableParallelism</span>(); 389<span class="hljs-keyword">const</span> process = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>); 390 391<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 392 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Primary <span class="hljs-subst">${process.pid}</span> is running`</span>); 393 394 <span class="hljs-comment">// Fork workers.</span> 395 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 396 cluster.<span class="hljs-title function_">fork</span>(); 397 } 398 399 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 400 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker <span class="hljs-subst">${worker.process.pid}</span> died`</span>); 401 }); 402} <span class="hljs-keyword">else</span> { 403 <span class="hljs-comment">// Workers can share any TCP connection</span> 404 <span class="hljs-comment">// In this case it is an HTTP server</span> 405 http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 406 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 407 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'hello world\n'</span>); 408 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 409 410 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Worker <span class="hljs-subst">${process.pid}</span> started`</span>); 411}</code><button class="copy-button">copy</button></pre> 412<p>Running Node.js will now share port 8000 between the workers:</p> 413<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node server.js</span> 414Primary 3596 is running 415Worker 4324 started 416Worker 4520 started 417Worker 6056 started 418Worker 5644 started</code> <button class="copy-button">copy</button></pre> 419<p>On Windows, it is not yet possible to set up a named pipe server in a worker.</p> 420<section><h3>How it works<span><a class="mark" href="#how-it-works" id="how-it-works">#</a></span><a aria-hidden="true" class="legacy" id="cluster_how_it_works"></a></h3> 421 422<p>The worker processes are spawned using the <a href="child_process.html#child_processforkmodulepath-args-options"><code>child_process.fork()</code></a> method, 423so that they can communicate with the parent via IPC and pass server 424handles back and forth.</p> 425<p>The cluster module supports two methods of distributing incoming 426connections.</p> 427<p>The first one (and the default one on all platforms except Windows) 428is the round-robin approach, where the primary process listens on a 429port, accepts new connections and distributes them across the workers 430in a round-robin fashion, with some built-in smarts to avoid 431overloading a worker process.</p> 432<p>The second approach is where the primary process creates the listen 433socket and sends it to interested workers. The workers then accept 434incoming connections directly.</p> 435<p>The second approach should, in theory, give the best performance. 436In practice however, distribution tends to be very unbalanced due 437to operating system scheduler vagaries. Loads have been observed 438where over 70% of all connections ended up in just two processes, 439out of a total of eight.</p> 440<p>Because <code>server.listen()</code> hands off most of the work to the primary 441process, there are three cases where the behavior between a normal 442Node.js process and a cluster worker differs:</p> 443<ol> 444<li><code>server.listen({fd: 7})</code> Because the message is passed to the primary, 445file descriptor 7 <strong>in the parent</strong> will be listened on, and the 446handle passed to the worker, rather than listening to the worker's 447idea of what the number 7 file descriptor references.</li> 448<li><code>server.listen(handle)</code> Listening on handles explicitly will cause 449the worker to use the supplied handle, rather than talk to the primary 450process.</li> 451<li><code>server.listen(0)</code> Normally, this will cause servers to listen on a 452random port. However, in a cluster, each worker will receive the 453same "random" port each time they do <code>listen(0)</code>. In essence, the 454port is random the first time, but predictable thereafter. To listen 455on a unique port, generate a port number based on the cluster worker ID.</li> 456</ol> 457<p>Node.js does not provide routing logic. It is therefore important to design an 458application such that it does not rely too heavily on in-memory data objects for 459things like sessions and login.</p> 460<p>Because workers are all separate processes, they can be killed or 461re-spawned depending on a program's needs, without affecting other 462workers. As long as there are some workers still alive, the server will 463continue to accept connections. If no workers are alive, existing connections 464will be dropped and new connections will be refused. Node.js does not 465automatically manage the number of workers, however. It is the application's 466responsibility to manage the worker pool based on its own needs.</p> 467<p>Although a primary use case for the <code>node:cluster</code> module is networking, it can 468also be used for other use cases requiring worker processes.</p> 469</section><section><h3>Class: <code>Worker</code><span><a class="mark" href="#class-worker" id="class-worker">#</a></span><a aria-hidden="true" class="legacy" id="cluster_class_worker"></a></h3> 470<div class="api_metadata"> 471<span>Added in: v0.7.0</span> 472</div> 473<ul> 474<li>Extends: <a href="events.html#class-eventemitter" class="type"><EventEmitter></a></li> 475</ul> 476<p>A <code>Worker</code> object contains all public information and method about a worker. 477In the primary it can be obtained using <code>cluster.workers</code>. In a worker 478it can be obtained using <code>cluster.worker</code>.</p> 479<h4>Event: <code>'disconnect'</code><span><a class="mark" href="#event-disconnect" id="event-disconnect">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_disconnect"></a></h4> 480<div class="api_metadata"> 481<span>Added in: v0.7.7</span> 482</div> 483<p>Similar to the <code>cluster.on('disconnect')</code> event, but specific to this worker.</p> 484<pre><code class="language-js">cluster.<span class="hljs-title function_">fork</span>().<span class="hljs-title function_">on</span>(<span class="hljs-string">'disconnect'</span>, <span class="hljs-function">() =></span> { 485 <span class="hljs-comment">// Worker has disconnected</span> 486});</code> <button class="copy-button">copy</button></pre> 487<h4>Event: <code>'error'</code><span><a class="mark" href="#event-error" id="event-error">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_error"></a></h4> 488<div class="api_metadata"> 489<span>Added in: v0.7.3</span> 490</div> 491<p>This event is the same as the one provided by <a href="child_process.html#child_processforkmodulepath-args-options"><code>child_process.fork()</code></a>.</p> 492<p>Within a worker, <code>process.on('error')</code> may also be used.</p> 493<h4>Event: <code>'exit'</code><span><a class="mark" href="#event-exit" id="event-exit">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_exit"></a></h4> 494<div class="api_metadata"> 495<span>Added in: v0.11.2</span> 496</div> 497<ul> 498<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The exit code, if it exited normally.</li> 499<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the signal (e.g. <code>'SIGHUP'</code>) that caused 500the process to be killed.</li> 501</ul> 502<p>Similar to the <code>cluster.on('exit')</code> event, but specific to this worker.</p> 503 504<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 505 506<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 507 <span class="hljs-keyword">const</span> worker = cluster.<span class="hljs-title function_">fork</span>(); 508 worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">code, signal</span>) =></span> { 509 <span class="hljs-keyword">if</span> (signal) { 510 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker was killed by signal: <span class="hljs-subst">${signal}</span>`</span>); 511 } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (code !== <span class="hljs-number">0</span>) { 512 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker exited with error code: <span class="hljs-subst">${code}</span>`</span>); 513 } <span class="hljs-keyword">else</span> { 514 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker success!'</span>); 515 } 516 }); 517}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 518 519<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 520 <span class="hljs-keyword">const</span> worker = cluster.<span class="hljs-title function_">fork</span>(); 521 worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">code, signal</span>) =></span> { 522 <span class="hljs-keyword">if</span> (signal) { 523 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker was killed by signal: <span class="hljs-subst">${signal}</span>`</span>); 524 } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (code !== <span class="hljs-number">0</span>) { 525 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`worker exited with error code: <span class="hljs-subst">${code}</span>`</span>); 526 } <span class="hljs-keyword">else</span> { 527 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker success!'</span>); 528 } 529 }); 530}</code><button class="copy-button">copy</button></pre> 531<h4>Event: <code>'listening'</code><span><a class="mark" href="#event-listening" id="event-listening">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_listening"></a></h4> 532<div class="api_metadata"> 533<span>Added in: v0.7.0</span> 534</div> 535<ul> 536<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 537</ul> 538<p>Similar to the <code>cluster.on('listening')</code> event, but specific to this worker.</p> 539 540<pre class="with-45-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs">cluster.<span class="hljs-title function_">fork</span>().<span class="hljs-title function_">on</span>(<span class="hljs-string">'listening'</span>, <span class="hljs-function">(<span class="hljs-params">address</span>) =></span> { 541 <span class="hljs-comment">// Worker is listening</span> 542});</code><code class="language-js cjs">cluster.<span class="hljs-title function_">fork</span>().<span class="hljs-title function_">on</span>(<span class="hljs-string">'listening'</span>, <span class="hljs-function">(<span class="hljs-params">address</span>) =></span> { 543 <span class="hljs-comment">// Worker is listening</span> 544});</code><button class="copy-button">copy</button></pre> 545<p>It is not emitted in the worker.</p> 546<h4>Event: <code>'message'</code><span><a class="mark" href="#event-message" id="event-message">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_message"></a></h4> 547<div class="api_metadata"> 548<span>Added in: v0.7.0</span> 549</div> 550<ul> 551<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 552<li><code>handle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 553</ul> 554<p>Similar to the <code>'message'</code> event of <code>cluster</code>, but specific to this worker.</p> 555<p>Within a worker, <code>process.on('message')</code> may also be used.</p> 556<p>See <a href="process.html#event-message"><code>process</code> event: <code>'message'</code></a>.</p> 557<p>Here is an example using the message system. It keeps a count in the primary 558process of the number of HTTP requests received by the workers:</p> 559 560<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 561<span class="hljs-keyword">import</span> http <span class="hljs-keyword">from</span> <span class="hljs-string">'node:http'</span>; 562<span class="hljs-keyword">import</span> { availableParallelism } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:os'</span>; 563<span class="hljs-keyword">import</span> process <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 564 565<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 566 567 <span class="hljs-comment">// Keep track of http requests</span> 568 <span class="hljs-keyword">let</span> numReqs = <span class="hljs-number">0</span>; 569 <span class="hljs-built_in">setInterval</span>(<span class="hljs-function">() =></span> { 570 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`numReqs = <span class="hljs-subst">${numReqs}</span>`</span>); 571 }, <span class="hljs-number">1000</span>); 572 573 <span class="hljs-comment">// Count requests</span> 574 <span class="hljs-keyword">function</span> <span class="hljs-title function_">messageHandler</span>(<span class="hljs-params">msg</span>) { 575 <span class="hljs-keyword">if</span> (msg.<span class="hljs-property">cmd</span> && msg.<span class="hljs-property">cmd</span> === <span class="hljs-string">'notifyRequest'</span>) { 576 numReqs += <span class="hljs-number">1</span>; 577 } 578 } 579 580 <span class="hljs-comment">// Start workers and listen for messages containing notifyRequest</span> 581 <span class="hljs-keyword">const</span> numCPUs = <span class="hljs-title function_">availableParallelism</span>(); 582 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 583 cluster.<span class="hljs-title function_">fork</span>(); 584 } 585 586 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> id <span class="hljs-keyword">in</span> cluster.<span class="hljs-property">workers</span>) { 587 cluster.<span class="hljs-property">workers</span>[id].<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, messageHandler); 588 } 589 590} <span class="hljs-keyword">else</span> { 591 592 <span class="hljs-comment">// Worker processes have a http server.</span> 593 http.<span class="hljs-title class_">Server</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 594 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 595 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'hello world\n'</span>); 596 597 <span class="hljs-comment">// Notify primary about the request</span> 598 process.<span class="hljs-title function_">send</span>({ <span class="hljs-attr">cmd</span>: <span class="hljs-string">'notifyRequest'</span> }); 599 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 600}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 601<span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 602<span class="hljs-keyword">const</span> process = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>); 603 604<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 605 606 <span class="hljs-comment">// Keep track of http requests</span> 607 <span class="hljs-keyword">let</span> numReqs = <span class="hljs-number">0</span>; 608 <span class="hljs-built_in">setInterval</span>(<span class="hljs-function">() =></span> { 609 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`numReqs = <span class="hljs-subst">${numReqs}</span>`</span>); 610 }, <span class="hljs-number">1000</span>); 611 612 <span class="hljs-comment">// Count requests</span> 613 <span class="hljs-keyword">function</span> <span class="hljs-title function_">messageHandler</span>(<span class="hljs-params">msg</span>) { 614 <span class="hljs-keyword">if</span> (msg.<span class="hljs-property">cmd</span> && msg.<span class="hljs-property">cmd</span> === <span class="hljs-string">'notifyRequest'</span>) { 615 numReqs += <span class="hljs-number">1</span>; 616 } 617 } 618 619 <span class="hljs-comment">// Start workers and listen for messages containing notifyRequest</span> 620 <span class="hljs-keyword">const</span> numCPUs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:os'</span>).<span class="hljs-title function_">availableParallelism</span>(); 621 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 622 cluster.<span class="hljs-title function_">fork</span>(); 623 } 624 625 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> id <span class="hljs-keyword">in</span> cluster.<span class="hljs-property">workers</span>) { 626 cluster.<span class="hljs-property">workers</span>[id].<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, messageHandler); 627 } 628 629} <span class="hljs-keyword">else</span> { 630 631 <span class="hljs-comment">// Worker processes have a http server.</span> 632 http.<span class="hljs-title class_">Server</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 633 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 634 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'hello world\n'</span>); 635 636 <span class="hljs-comment">// Notify primary about the request</span> 637 process.<span class="hljs-title function_">send</span>({ <span class="hljs-attr">cmd</span>: <span class="hljs-string">'notifyRequest'</span> }); 638 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 639}</code><button class="copy-button">copy</button></pre> 640<h4>Event: <code>'online'</code><span><a class="mark" href="#event-online" id="event-online">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_online"></a></h4> 641<div class="api_metadata"> 642<span>Added in: v0.7.0</span> 643</div> 644<p>Similar to the <code>cluster.on('online')</code> event, but specific to this worker.</p> 645<pre><code class="language-js">cluster.<span class="hljs-title function_">fork</span>().<span class="hljs-title function_">on</span>(<span class="hljs-string">'online'</span>, <span class="hljs-function">() =></span> { 646 <span class="hljs-comment">// Worker is online</span> 647});</code> <button class="copy-button">copy</button></pre> 648<p>It is not emitted in the worker.</p> 649<h4><code>worker.disconnect()</code><span><a class="mark" href="#workerdisconnect" id="workerdisconnect">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_disconnect"></a></h4> 650<div class="api_metadata"> 651<details class="changelog"><summary>History</summary> 652<table> 653<tbody><tr><th>Version</th><th>Changes</th></tr> 654<tr><td>v7.3.0</td> 655<td><p>This method now returns a reference to <code>worker</code>.</p></td></tr> 656<tr><td>v0.7.7</td> 657<td><p><span>Added in: v0.7.7</span></p></td></tr> 658</tbody></table> 659</details> 660</div> 661<ul> 662<li>Returns: <a href="cluster.html#class-worker" class="type"><cluster.Worker></a> A reference to <code>worker</code>.</li> 663</ul> 664<p>In a worker, this function will close all servers, wait for the <code>'close'</code> event 665on those servers, and then disconnect the IPC channel.</p> 666<p>In the primary, an internal message is sent to the worker causing it to call 667<code>.disconnect()</code> on itself.</p> 668<p>Causes <code>.exitedAfterDisconnect</code> to be set.</p> 669<p>After a server is closed, it will no longer accept new connections, 670but connections may be accepted by any other listening worker. Existing 671connections will be allowed to close as usual. When no more connections exist, 672see <a href="net.html#event-close"><code>server.close()</code></a>, the IPC channel to the worker will close allowing it 673to die gracefully.</p> 674<p>The above applies <em>only</em> to server connections, client connections are not 675automatically closed by workers, and disconnect does not wait for them to close 676before exiting.</p> 677<p>In a worker, <code>process.disconnect</code> exists, but it is not this function; 678it is <a href="child_process.html#subprocessdisconnect"><code>disconnect()</code></a>.</p> 679<p>Because long living server connections may block workers from disconnecting, it 680may be useful to send a message, so application specific actions may be taken to 681close them. It also may be useful to implement a timeout, killing a worker if 682the <code>'disconnect'</code> event has not been emitted after some time.</p> 683<pre><code class="language-js"><span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 684 <span class="hljs-keyword">const</span> worker = cluster.<span class="hljs-title function_">fork</span>(); 685 <span class="hljs-keyword">let</span> timeout; 686 687 worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'listening'</span>, <span class="hljs-function">(<span class="hljs-params">address</span>) =></span> { 688 worker.<span class="hljs-title function_">send</span>(<span class="hljs-string">'shutdown'</span>); 689 worker.<span class="hljs-title function_">disconnect</span>(); 690 timeout = <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 691 worker.<span class="hljs-title function_">kill</span>(); 692 }, <span class="hljs-number">2000</span>); 693 }); 694 695 worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'disconnect'</span>, <span class="hljs-function">() =></span> { 696 <span class="hljs-built_in">clearTimeout</span>(timeout); 697 }); 698 699} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isWorker</span>) { 700 <span class="hljs-keyword">const</span> net = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:net'</span>); 701 <span class="hljs-keyword">const</span> server = net.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">socket</span>) =></span> { 702 <span class="hljs-comment">// Connections never end</span> 703 }); 704 705 server.<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 706 707 process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> { 708 <span class="hljs-keyword">if</span> (msg === <span class="hljs-string">'shutdown'</span>) { 709 <span class="hljs-comment">// Initiate graceful close of any connections to server</span> 710 } 711 }); 712}</code> <button class="copy-button">copy</button></pre> 713<h4><code>worker.exitedAfterDisconnect</code><span><a class="mark" href="#workerexitedafterdisconnect" id="workerexitedafterdisconnect">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_exitedafterdisconnect"></a></h4> 714<div class="api_metadata"> 715<span>Added in: v6.0.0</span> 716</div> 717<ul> 718<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 719</ul> 720<p>This property is <code>true</code> if the worker exited due to <code>.disconnect()</code>. 721If the worker exited any other way, it is <code>false</code>. If the 722worker has not exited, it is <code>undefined</code>.</p> 723<p>The boolean <a href="#workerexitedafterdisconnect"><code>worker.exitedAfterDisconnect</code></a> allows distinguishing between 724voluntary and accidental exit, the primary may choose not to respawn a worker 725based on this value.</p> 726<pre><code class="language-js">cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 727 <span class="hljs-keyword">if</span> (worker.<span class="hljs-property">exitedAfterDisconnect</span> === <span class="hljs-literal">true</span>) { 728 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Oh, it was just voluntary – no need to worry'</span>); 729 } 730}); 731 732<span class="hljs-comment">// kill worker</span> 733worker.<span class="hljs-title function_">kill</span>();</code> <button class="copy-button">copy</button></pre> 734<h4><code>worker.id</code><span><a class="mark" href="#workerid" id="workerid">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_id"></a></h4> 735<div class="api_metadata"> 736<span>Added in: v0.8.0</span> 737</div> 738<ul> 739<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a></li> 740</ul> 741<p>Each new worker is given its own unique id, this id is stored in the 742<code>id</code>.</p> 743<p>While a worker is alive, this is the key that indexes it in 744<code>cluster.workers</code>.</p> 745<h4><code>worker.isConnected()</code><span><a class="mark" href="#workerisconnected" id="workerisconnected">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_isconnected"></a></h4> 746<div class="api_metadata"> 747<span>Added in: v0.11.14</span> 748</div> 749<p>This function returns <code>true</code> if the worker is connected to its primary via its 750IPC channel, <code>false</code> otherwise. A worker is connected to its primary after it 751has been created. It is disconnected after the <code>'disconnect'</code> event is emitted.</p> 752<h4><code>worker.isDead()</code><span><a class="mark" href="#workerisdead" id="workerisdead">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_isdead"></a></h4> 753<div class="api_metadata"> 754<span>Added in: v0.11.14</span> 755</div> 756<p>This function returns <code>true</code> if the worker's process has terminated (either 757because of exiting or being signaled). Otherwise, it returns <code>false</code>.</p> 758 759<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 760<span class="hljs-keyword">import</span> http <span class="hljs-keyword">from</span> <span class="hljs-string">'node:http'</span>; 761<span class="hljs-keyword">import</span> { availableParallelism } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:os'</span>; 762<span class="hljs-keyword">import</span> process <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 763 764<span class="hljs-keyword">const</span> numCPUs = <span class="hljs-title function_">availableParallelism</span>(); 765 766<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 767 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Primary <span class="hljs-subst">${process.pid}</span> is running`</span>); 768 769 <span class="hljs-comment">// Fork workers.</span> 770 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 771 cluster.<span class="hljs-title function_">fork</span>(); 772 } 773 774 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'fork'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 775 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker is dead:'</span>, worker.<span class="hljs-title function_">isDead</span>()); 776 }); 777 778 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 779 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker is dead:'</span>, worker.<span class="hljs-title function_">isDead</span>()); 780 }); 781} <span class="hljs-keyword">else</span> { 782 <span class="hljs-comment">// Workers can share any TCP connection. In this case, it is an HTTP server.</span> 783 http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 784 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 785 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">`Current process\n <span class="hljs-subst">${process.pid}</span>`</span>); 786 process.<span class="hljs-title function_">kill</span>(process.<span class="hljs-property">pid</span>); 787 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 788}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 789<span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 790<span class="hljs-keyword">const</span> numCPUs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:os'</span>).<span class="hljs-title function_">availableParallelism</span>(); 791<span class="hljs-keyword">const</span> process = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>); 792 793<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 794 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Primary <span class="hljs-subst">${process.pid}</span> is running`</span>); 795 796 <span class="hljs-comment">// Fork workers.</span> 797 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numCPUs; i++) { 798 cluster.<span class="hljs-title function_">fork</span>(); 799 } 800 801 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'fork'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 802 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker is dead:'</span>, worker.<span class="hljs-title function_">isDead</span>()); 803 }); 804 805 cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 806 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker is dead:'</span>, worker.<span class="hljs-title function_">isDead</span>()); 807 }); 808} <span class="hljs-keyword">else</span> { 809 <span class="hljs-comment">// Workers can share any TCP connection. In this case, it is an HTTP server.</span> 810 http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 811 res.<span class="hljs-title function_">writeHead</span>(<span class="hljs-number">200</span>); 812 res.<span class="hljs-title function_">end</span>(<span class="hljs-string">`Current process\n <span class="hljs-subst">${process.pid}</span>`</span>); 813 process.<span class="hljs-title function_">kill</span>(process.<span class="hljs-property">pid</span>); 814 }).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8000</span>); 815}</code><button class="copy-button">copy</button></pre> 816<h4><code>worker.kill([signal])</code><span><a class="mark" href="#workerkillsignal" id="workerkillsignal">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_kill_signal"></a></h4> 817<div class="api_metadata"> 818<span>Added in: v0.9.12</span> 819</div> 820<ul> 821<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Name of the kill signal to send to the worker 822process. <strong>Default:</strong> <code>'SIGTERM'</code></li> 823</ul> 824<p>This function will kill the worker. In the primary worker, it does this by 825disconnecting the <code>worker.process</code>, and once disconnected, killing with 826<code>signal</code>. In the worker, it does it by killing the process with <code>signal</code>.</p> 827<p>The <code>kill()</code> function kills the worker process without waiting for a graceful 828disconnect, it has the same behavior as <code>worker.process.kill()</code>.</p> 829<p>This method is aliased as <code>worker.destroy()</code> for backwards compatibility.</p> 830<p>In a worker, <code>process.kill()</code> exists, but it is not this function; 831it is <a href="process.html#processkillpid-signal"><code>kill()</code></a>.</p> 832<h4><code>worker.process</code><span><a class="mark" href="#workerprocess" id="workerprocess">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_process"></a></h4> 833<div class="api_metadata"> 834<span>Added in: v0.7.0</span> 835</div> 836<ul> 837<li><a href="child_process.html#class-childprocess" class="type"><ChildProcess></a></li> 838</ul> 839<p>All workers are created using <a href="child_process.html#child_processforkmodulepath-args-options"><code>child_process.fork()</code></a>, the returned object 840from this function is stored as <code>.process</code>. In a worker, the global <code>process</code> 841is stored.</p> 842<p>See: <a href="child_process.html#child_processforkmodulepath-args-options">Child Process module</a>.</p> 843<p>Workers will call <code>process.exit(0)</code> if the <code>'disconnect'</code> event occurs 844on <code>process</code> and <code>.exitedAfterDisconnect</code> is not <code>true</code>. This protects against 845accidental disconnection.</p> 846<h4><code>worker.send(message[, sendHandle[, options]][, callback])</code><span><a class="mark" href="#workersendmessage-sendhandle-options-callback" id="workersendmessage-sendhandle-options-callback">#</a></span><a aria-hidden="true" class="legacy" id="cluster_worker_send_message_sendhandle_options_callback"></a></h4> 847<div class="api_metadata"> 848<details class="changelog"><summary>History</summary> 849<table> 850<tbody><tr><th>Version</th><th>Changes</th></tr> 851<tr><td>v4.0.0</td> 852<td><p>The <code>callback</code> parameter is supported now.</p></td></tr> 853<tr><td>v0.7.0</td> 854<td><p><span>Added in: v0.7.0</span></p></td></tr> 855</tbody></table> 856</details> 857</div> 858<ul> 859<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 860<li><code>sendHandle</code> <a href="net.html#serverlistenhandle-backlog-callback" class="type"><Handle></a></li> 861<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The <code>options</code> argument, if present, is an object used to 862parameterize the sending of certain types of handles. <code>options</code> supports 863the following properties: 864<ul> 865<li><code>keepOpen</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> A value that can be used when passing instances of 866<code>net.Socket</code>. When <code>true</code>, the socket is kept open in the sending process. 867<strong>Default:</strong> <code>false</code>.</li> 868</ul> 869</li> 870<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 871<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 872</ul> 873<p>Send a message to a worker or primary, optionally with a handle.</p> 874<p>In the primary, this sends a message to a specific worker. It is identical to 875<a href="child_process.html#subprocesssendmessage-sendhandle-options-callback"><code>ChildProcess.send()</code></a>.</p> 876<p>In a worker, this sends a message to the primary. It is identical to 877<code>process.send()</code>.</p> 878<p>This example will echo back all messages from the primary:</p> 879<pre><code class="language-js"><span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 880 <span class="hljs-keyword">const</span> worker = cluster.<span class="hljs-title function_">fork</span>(); 881 worker.<span class="hljs-title function_">send</span>(<span class="hljs-string">'hi there'</span>); 882 883} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isWorker</span>) { 884 process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> { 885 process.<span class="hljs-title function_">send</span>(msg); 886 }); 887}</code> <button class="copy-button">copy</button></pre> 888</section><section><h3>Event: <code>'disconnect'</code><span><a class="mark" href="#event-disconnect_1" id="event-disconnect_1">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_disconnect_1"></a></h3> 889<div class="api_metadata"> 890<span>Added in: v0.7.9</span> 891</div> 892<ul> 893<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 894</ul> 895<p>Emitted after the worker IPC channel has disconnected. This can occur when a 896worker exits gracefully, is killed, or is disconnected manually (such as with 897<code>worker.disconnect()</code>).</p> 898<p>There may be a delay between the <code>'disconnect'</code> and <code>'exit'</code> events. These 899events can be used to detect if the process is stuck in a cleanup or if there 900are long-living connections.</p> 901<pre><code class="language-js">cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'disconnect'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 902 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`The worker #<span class="hljs-subst">${worker.id}</span> has disconnected`</span>); 903});</code> <button class="copy-button">copy</button></pre> 904</section><section><h3>Event: <code>'exit'</code><span><a class="mark" href="#event-exit_1" id="event-exit_1">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_exit_1"></a></h3> 905<div class="api_metadata"> 906<span>Added in: v0.7.9</span> 907</div> 908<ul> 909<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 910<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The exit code, if it exited normally.</li> 911<li><code>signal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the signal (e.g. <code>'SIGHUP'</code>) that caused 912the process to be killed.</li> 913</ul> 914<p>When any of the workers die the cluster module will emit the <code>'exit'</code> event.</p> 915<p>This can be used to restart the worker by calling <a href="#clusterforkenv"><code>.fork()</code></a> again.</p> 916<pre><code class="language-js">cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 917 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'worker %d died (%s). restarting...'</span>, 918 worker.<span class="hljs-property">process</span>.<span class="hljs-property">pid</span>, signal || code); 919 cluster.<span class="hljs-title function_">fork</span>(); 920});</code> <button class="copy-button">copy</button></pre> 921<p>See <a href="child_process.html#event-exit"><code>child_process</code> event: <code>'exit'</code></a>.</p> 922</section><section><h3>Event: <code>'fork'</code><span><a class="mark" href="#event-fork" id="event-fork">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_fork"></a></h3> 923<div class="api_metadata"> 924<span>Added in: v0.7.0</span> 925</div> 926<ul> 927<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 928</ul> 929<p>When a new worker is forked the cluster module will emit a <code>'fork'</code> event. 930This can be used to log worker activity, and create a custom timeout.</p> 931<pre><code class="language-js"><span class="hljs-keyword">const</span> timeouts = []; 932<span class="hljs-keyword">function</span> <span class="hljs-title function_">errorMsg</span>(<span class="hljs-params"></span>) { 933 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">'Something must be wrong with the connection ...'</span>); 934} 935 936cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'fork'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 937 timeouts[worker.<span class="hljs-property">id</span>] = <span class="hljs-built_in">setTimeout</span>(errorMsg, <span class="hljs-number">2000</span>); 938}); 939cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'listening'</span>, <span class="hljs-function">(<span class="hljs-params">worker, address</span>) =></span> { 940 <span class="hljs-built_in">clearTimeout</span>(timeouts[worker.<span class="hljs-property">id</span>]); 941}); 942cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">worker, code, signal</span>) =></span> { 943 <span class="hljs-built_in">clearTimeout</span>(timeouts[worker.<span class="hljs-property">id</span>]); 944 <span class="hljs-title function_">errorMsg</span>(); 945});</code> <button class="copy-button">copy</button></pre> 946</section><section><h3>Event: <code>'listening'</code><span><a class="mark" href="#event-listening_1" id="event-listening_1">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_listening_1"></a></h3> 947<div class="api_metadata"> 948<span>Added in: v0.7.0</span> 949</div> 950<ul> 951<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 952<li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 953</ul> 954<p>After calling <code>listen()</code> from a worker, when the <code>'listening'</code> event is emitted 955on the server, a <code>'listening'</code> event will also be emitted on <code>cluster</code> in the 956primary.</p> 957<p>The event handler is executed with two arguments, the <code>worker</code> contains the 958worker object and the <code>address</code> object contains the following connection 959properties: <code>address</code>, <code>port</code>, and <code>addressType</code>. This is very useful if the 960worker is listening on more than one address.</p> 961<pre><code class="language-js">cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'listening'</span>, <span class="hljs-function">(<span class="hljs-params">worker, address</span>) =></span> { 962 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>( 963 <span class="hljs-string">`A worker is now connected to <span class="hljs-subst">${address.address}</span>:<span class="hljs-subst">${address.port}</span>`</span>); 964});</code> <button class="copy-button">copy</button></pre> 965<p>The <code>addressType</code> is one of:</p> 966<ul> 967<li><code>4</code> (TCPv4)</li> 968<li><code>6</code> (TCPv6)</li> 969<li><code>-1</code> (Unix domain socket)</li> 970<li><code>'udp4'</code> or <code>'udp6'</code> (UDPv4 or UDPv6)</li> 971</ul> 972</section><section><h3>Event: <code>'message'</code><span><a class="mark" href="#event-message_1" id="event-message_1">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_message_1"></a></h3> 973<div class="api_metadata"> 974<details class="changelog"><summary>History</summary> 975<table> 976<tbody><tr><th>Version</th><th>Changes</th></tr> 977<tr><td>v6.0.0</td> 978<td><p>The <code>worker</code> parameter is passed now; see below for details.</p></td></tr> 979<tr><td>v2.5.0</td> 980<td><p><span>Added in: v2.5.0</span></p></td></tr> 981</tbody></table> 982</details> 983</div> 984<ul> 985<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 986<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 987<li><code>handle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 988</ul> 989<p>Emitted when the cluster primary receives a message from any worker.</p> 990<p>See <a href="child_process.html#event-message"><code>child_process</code> event: <code>'message'</code></a>.</p> 991</section><section><h3>Event: <code>'online'</code><span><a class="mark" href="#event-online_1" id="event-online_1">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_online_1"></a></h3> 992<div class="api_metadata"> 993<span>Added in: v0.7.0</span> 994</div> 995<ul> 996<li><code>worker</code> <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 997</ul> 998<p>After forking a new worker, the worker should respond with an online message. 999When the primary receives an online message it will emit this event. 1000The difference between <code>'fork'</code> and <code>'online'</code> is that fork is emitted when the 1001primary forks a worker, and <code>'online'</code> is emitted when the worker is running.</p> 1002<pre><code class="language-js">cluster.<span class="hljs-title function_">on</span>(<span class="hljs-string">'online'</span>, <span class="hljs-function">(<span class="hljs-params">worker</span>) =></span> { 1003 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Yay, the worker responded after it was forked'</span>); 1004});</code> <button class="copy-button">copy</button></pre> 1005</section><section><h3>Event: <code>'setup'</code><span><a class="mark" href="#event-setup" id="event-setup">#</a></span><a aria-hidden="true" class="legacy" id="cluster_event_setup"></a></h3> 1006<div class="api_metadata"> 1007<span>Added in: v0.7.1</span> 1008</div> 1009<ul> 1010<li><code>settings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 1011</ul> 1012<p>Emitted every time <a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a> is called.</p> 1013<p>The <code>settings</code> object is the <code>cluster.settings</code> object at the time 1014<a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a> was called and is advisory only, since multiple calls to 1015<a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a> can be made in a single tick.</p> 1016<p>If accuracy is important, use <code>cluster.settings</code>.</p> 1017</section><section><h3><code>cluster.disconnect([callback])</code><span><a class="mark" href="#clusterdisconnectcallback" id="clusterdisconnectcallback">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_disconnect_callback"></a></h3> 1018<div class="api_metadata"> 1019<span>Added in: v0.7.7</span> 1020</div> 1021<ul> 1022<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Called when all workers are disconnected and handles are 1023closed.</li> 1024</ul> 1025<p>Calls <code>.disconnect()</code> on each worker in <code>cluster.workers</code>.</p> 1026<p>When they are disconnected all internal handles will be closed, allowing the 1027primary process to die gracefully if no other event is waiting.</p> 1028<p>The method takes an optional callback argument which will be called when 1029finished.</p> 1030<p>This can only be called from the primary process.</p> 1031</section><section><h3><code>cluster.fork([env])</code><span><a class="mark" href="#clusterforkenv" id="clusterforkenv">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_fork_env"></a></h3> 1032<div class="api_metadata"> 1033<span>Added in: v0.6.0</span> 1034</div> 1035<ul> 1036<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Key/value pairs to add to worker process environment.</li> 1037<li>Returns: <a href="cluster.html#class-worker" class="type"><cluster.Worker></a></li> 1038</ul> 1039<p>Spawn a new worker process.</p> 1040<p>This can only be called from the primary process.</p> 1041</section><section><h3><code>cluster.isMaster</code><span><a class="mark" href="#clusterismaster" id="clusterismaster">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_ismaster"></a></h3> 1042<div class="api_metadata"> 1043<span>Added in: v0.8.1</span><span>Deprecated since: v16.0.0</span> 1044</div> 1045<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p> 1046<p>Deprecated alias for <a href="#clusterisprimary"><code>cluster.isPrimary</code></a>.</p> 1047</section><section><h3><code>cluster.isPrimary</code><span><a class="mark" href="#clusterisprimary" id="clusterisprimary">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_isprimary"></a></h3> 1048<div class="api_metadata"> 1049<span>Added in: v16.0.0</span> 1050</div> 1051<ul> 1052<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 1053</ul> 1054<p>True if the process is a primary. This is determined 1055by the <code>process.env.NODE_UNIQUE_ID</code>. If <code>process.env.NODE_UNIQUE_ID</code> is 1056undefined, then <code>isPrimary</code> is <code>true</code>.</p> 1057</section><section><h3><code>cluster.isWorker</code><span><a class="mark" href="#clusterisworker" id="clusterisworker">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_isworker"></a></h3> 1058<div class="api_metadata"> 1059<span>Added in: v0.6.0</span> 1060</div> 1061<ul> 1062<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 1063</ul> 1064<p>True if the process is not a primary (it is the negation of <code>cluster.isPrimary</code>).</p> 1065</section><section><h3><code>cluster.schedulingPolicy</code><span><a class="mark" href="#clusterschedulingpolicy" id="clusterschedulingpolicy">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_schedulingpolicy"></a></h3> 1066<div class="api_metadata"> 1067<span>Added in: v0.11.2</span> 1068</div> 1069<p>The scheduling policy, either <code>cluster.SCHED_RR</code> for round-robin or 1070<code>cluster.SCHED_NONE</code> to leave it to the operating system. This is a 1071global setting and effectively frozen once either the first worker is spawned, 1072or <a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a> is called, whichever comes first.</p> 1073<p><code>SCHED_RR</code> is the default on all operating systems except Windows. 1074Windows will change to <code>SCHED_RR</code> once libuv is able to effectively 1075distribute IOCP handles without incurring a large performance hit.</p> 1076<p><code>cluster.schedulingPolicy</code> can also be set through the 1077<code>NODE_CLUSTER_SCHED_POLICY</code> environment variable. Valid 1078values are <code>'rr'</code> and <code>'none'</code>.</p> 1079</section><section><h3><code>cluster.settings</code><span><a class="mark" href="#clustersettings" id="clustersettings">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_settings"></a></h3> 1080<div class="api_metadata"> 1081<details class="changelog"><summary>History</summary> 1082<table> 1083<tbody><tr><th>Version</th><th>Changes</th></tr> 1084<tr><td>v13.2.0, v12.16.0</td> 1085<td><p>The <code>serialization</code> option is supported now.</p></td></tr> 1086<tr><td>v9.5.0</td> 1087<td><p>The <code>cwd</code> option is supported now.</p></td></tr> 1088<tr><td>v9.4.0</td> 1089<td><p>The <code>windowsHide</code> option is supported now.</p></td></tr> 1090<tr><td>v8.2.0</td> 1091<td><p>The <code>inspectPort</code> option is supported now.</p></td></tr> 1092<tr><td>v6.4.0</td> 1093<td><p>The <code>stdio</code> option is supported now.</p></td></tr> 1094<tr><td>v0.7.1</td> 1095<td><p><span>Added in: v0.7.1</span></p></td></tr> 1096</tbody></table> 1097</details> 1098</div> 1099<ul> 1100<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 1101<ul> 1102<li><code>execArgv</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> List of string arguments passed to the Node.js 1103executable. <strong>Default:</strong> <code>process.execArgv</code>.</li> 1104<li><code>exec</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> File path to worker file. <strong>Default:</strong> <code>process.argv[1]</code>.</li> 1105<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> String arguments passed to worker. 1106<strong>Default:</strong> <code>process.argv.slice(2)</code>.</li> 1107<li><code>cwd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Current working directory of the worker process. <strong>Default:</strong> 1108<code>undefined</code> (inherits from parent process).</li> 1109<li><code>serialization</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Specify the kind of serialization used for sending 1110messages between processes. Possible values are <code>'json'</code> and <code>'advanced'</code>. 1111See <a href="child_process.html#advanced-serialization">Advanced serialization for <code>child_process</code></a> for more details. 1112<strong>Default:</strong> <code>false</code>.</li> 1113<li><code>silent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Whether or not to send output to parent's stdio. 1114<strong>Default:</strong> <code>false</code>.</li> 1115<li><code>stdio</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> Configures the stdio of forked processes. Because the 1116cluster module relies on IPC to function, this configuration must contain an 1117<code>'ipc'</code> entry. When this option is provided, it overrides <code>silent</code>. See 1118<a href="child_process.html#child_processspawncommand-args-options"><code>child_process.spawn()</code></a>'s <a href="child_process.html#optionsstdio"><code>stdio</code></a>.</li> 1119<li><code>uid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Sets the user identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setuid.2.html"><code>setuid(2)</code></a>.)</li> 1120<li><code>gid</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Sets the group identity of the process. (See <a href="http://man7.org/linux/man-pages/man2/setgid.2.html"><code>setgid(2)</code></a>.)</li> 1121<li><code>inspectPort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> Sets inspector port of worker. 1122This can be a number, or a function that takes no arguments and returns a 1123number. By default each worker gets its own port, incremented from the 1124primary's <code>process.debugPort</code>.</li> 1125<li><code>windowsHide</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Hide the forked processes console window that would 1126normally be created on Windows systems. <strong>Default:</strong> <code>false</code>.</li> 1127</ul> 1128</li> 1129</ul> 1130<p>After calling <a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a> (or <a href="#clusterforkenv"><code>.fork()</code></a>) this settings object will 1131contain the settings, including the default values.</p> 1132<p>This object is not intended to be changed or set manually.</p> 1133</section><section><h3><code>cluster.setupMaster([settings])</code><span><a class="mark" href="#clustersetupmastersettings" id="clustersetupmastersettings">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_setupmaster_settings"></a></h3> 1134<div class="api_metadata"> 1135<details class="changelog"><summary>History</summary> 1136<table> 1137<tbody><tr><th>Version</th><th>Changes</th></tr> 1138<tr><td>v16.0.0</td> 1139<td><p><span>Deprecated since: v16.0.0</span></p></td></tr> 1140<tr><td>v6.4.0</td> 1141<td><p>The <code>stdio</code> option is supported now.</p></td></tr> 1142<tr><td>v0.7.1</td> 1143<td><p><span>Added in: v0.7.1</span></p></td></tr> 1144</tbody></table> 1145</details> 1146</div> 1147<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p> 1148<p>Deprecated alias for <a href="#clustersetupprimarysettings"><code>.setupPrimary()</code></a>.</p> 1149</section><section><h3><code>cluster.setupPrimary([settings])</code><span><a class="mark" href="#clustersetupprimarysettings" id="clustersetupprimarysettings">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_setupprimary_settings"></a></h3> 1150<div class="api_metadata"> 1151<span>Added in: v16.0.0</span> 1152</div> 1153<ul> 1154<li><code>settings</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> See <a href="#clustersettings"><code>cluster.settings</code></a>.</li> 1155</ul> 1156<p><code>setupPrimary</code> is used to change the default 'fork' behavior. Once called, 1157the settings will be present in <code>cluster.settings</code>.</p> 1158<p>Any settings changes only affect future calls to <a href="#clusterforkenv"><code>.fork()</code></a> and have no 1159effect on workers that are already running.</p> 1160<p>The only attribute of a worker that cannot be set via <code>.setupPrimary()</code> is 1161the <code>env</code> passed to <a href="#clusterforkenv"><code>.fork()</code></a>.</p> 1162<p>The defaults above apply to the first call only; the defaults for later 1163calls are the current values at the time of <code>cluster.setupPrimary()</code> is called.</p> 1164 1165<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 1166 1167cluster.<span class="hljs-title function_">setupPrimary</span>({ 1168 <span class="hljs-attr">exec</span>: <span class="hljs-string">'worker.js'</span>, 1169 <span class="hljs-attr">args</span>: [<span class="hljs-string">'--use'</span>, <span class="hljs-string">'https'</span>], 1170 <span class="hljs-attr">silent</span>: <span class="hljs-literal">true</span>, 1171}); 1172cluster.<span class="hljs-title function_">fork</span>(); <span class="hljs-comment">// https worker</span> 1173cluster.<span class="hljs-title function_">setupPrimary</span>({ 1174 <span class="hljs-attr">exec</span>: <span class="hljs-string">'worker.js'</span>, 1175 <span class="hljs-attr">args</span>: [<span class="hljs-string">'--use'</span>, <span class="hljs-string">'http'</span>], 1176}); 1177cluster.<span class="hljs-title function_">fork</span>(); <span class="hljs-comment">// http worker</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 1178 1179cluster.<span class="hljs-title function_">setupPrimary</span>({ 1180 <span class="hljs-attr">exec</span>: <span class="hljs-string">'worker.js'</span>, 1181 <span class="hljs-attr">args</span>: [<span class="hljs-string">'--use'</span>, <span class="hljs-string">'https'</span>], 1182 <span class="hljs-attr">silent</span>: <span class="hljs-literal">true</span>, 1183}); 1184cluster.<span class="hljs-title function_">fork</span>(); <span class="hljs-comment">// https worker</span> 1185cluster.<span class="hljs-title function_">setupPrimary</span>({ 1186 <span class="hljs-attr">exec</span>: <span class="hljs-string">'worker.js'</span>, 1187 <span class="hljs-attr">args</span>: [<span class="hljs-string">'--use'</span>, <span class="hljs-string">'http'</span>], 1188}); 1189cluster.<span class="hljs-title function_">fork</span>(); <span class="hljs-comment">// http worker</span></code><button class="copy-button">copy</button></pre> 1190<p>This can only be called from the primary process.</p> 1191</section><section><h3><code>cluster.worker</code><span><a class="mark" href="#clusterworker" id="clusterworker">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_worker"></a></h3> 1192<div class="api_metadata"> 1193<span>Added in: v0.7.0</span> 1194</div> 1195<ul> 1196<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 1197</ul> 1198<p>A reference to the current worker object. Not available in the primary process.</p> 1199 1200<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 1201 1202<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 1203 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'I am primary'</span>); 1204 cluster.<span class="hljs-title function_">fork</span>(); 1205 cluster.<span class="hljs-title function_">fork</span>(); 1206} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isWorker</span>) { 1207 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`I am worker #<span class="hljs-subst">${cluster.worker.id}</span>`</span>); 1208}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 1209 1210<span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isPrimary</span>) { 1211 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'I am primary'</span>); 1212 cluster.<span class="hljs-title function_">fork</span>(); 1213 cluster.<span class="hljs-title function_">fork</span>(); 1214} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (cluster.<span class="hljs-property">isWorker</span>) { 1215 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`I am worker #<span class="hljs-subst">${cluster.worker.id}</span>`</span>); 1216}</code><button class="copy-button">copy</button></pre> 1217</section><section><h3><code>cluster.workers</code><span><a class="mark" href="#clusterworkers" id="clusterworkers">#</a></span><a aria-hidden="true" class="legacy" id="cluster_cluster_workers"></a></h3> 1218<div class="api_metadata"> 1219<span>Added in: v0.7.0</span> 1220</div> 1221<ul> 1222<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 1223</ul> 1224<p>A hash that stores the active worker objects, keyed by <code>id</code> field. This makes it 1225easy to loop through all the workers. It is only available in the primary 1226process.</p> 1227<p>A worker is removed from <code>cluster.workers</code> after the worker has disconnected 1228<em>and</em> exited. The order between these two events cannot be determined in 1229advance. However, it is guaranteed that the removal from the <code>cluster.workers</code> 1230list happens before the last <code>'disconnect'</code> or <code>'exit'</code> event is emitted.</p> 1231 1232<pre class="with-40-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> cluster <span class="hljs-keyword">from</span> <span class="hljs-string">'node:cluster'</span>; 1233 1234<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> worker <span class="hljs-keyword">of</span> <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">values</span>(cluster.<span class="hljs-property">workers</span>)) { 1235 worker.<span class="hljs-title function_">send</span>(<span class="hljs-string">'big announcement to all workers'</span>); 1236}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:cluster'</span>); 1237 1238<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> worker <span class="hljs-keyword">of</span> <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">values</span>(cluster.<span class="hljs-property">workers</span>)) { 1239 worker.<span class="hljs-title function_">send</span>(<span class="hljs-string">'big announcement to all workers'</span>); 1240}</code><button class="copy-button">copy</button></pre></section> 1241 <!-- API END --> 1242 </div> 1243 </div> 1244 </div> 1245</body> 1246</html> 1247