text: const cluster = require("cluster");
  const os = require("os");
  const process = require("process");
  const runServer = require("./app");
  
  const numCPUs = os.cpus().length;
  
  // Todo: The request from the same user must go to the same child.
  
  if (cluster.isPrimary) {
    console.log(`Primary ${process.pid} is running`);
  
    // Fork workers.
    for (let i = 0; i < numCPUs; i++) {
      cluster.fork();
    }
  
    cluster.on("exit", (worker, code, signal) => {
      console.log(`worker ${worker.process.pid} died`);
    });
  } else {
    runServer();
    console.log(`Worker ${process.pid} started`);
  }
  