)</code> function must be called only once or an
<code>EADDRINUSE</code> error will occur:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> cluster = <span class="hljs-built_in">require</span>(<span class="hljs-string">'cluster'</span>);
<span class="hljs-keyword">const</span> dgram = <span class="hljs-built_in">require</span>(<span class="hljs-string">'dgram'</span>);
<span class="hljs-keyword">if</span> (cluster.isMaster) {
  cluster.fork(); <span class="hljs-comment">// Works ok