How to fix Error: Worker already listening on same port (cluster port conflict) in Node.js

const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;

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 {
  // Workers share the same port
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('hello world\n');
  }).listen(8000);

  console.log(`Worker ${process.pid} started`);
}

const server = http.createServer((req, res) => {
  res.writeHead(200);
  res.end('hello world\n');
});

server.on('error', (err) => {
  if (err.code === 'EADDRINUSE') {
    console.error(`Port ${PORT} is already in use`);
    process.exit(1);
  } else {
    console.error('Server error:', err);
  }
});

server.listen(8000, () => {
  console.log(`Worker ${process.pid} listening on port 8000`);
});

// In primary process
cluster.on('message', (worker, message) => {
  if (message.cmd === 'restart') {
    console.log(`Restarting worker ${worker.id}`);
    worker.kill();
    cluster.fork();
  }
});

// In worker process - request restart instead of close/reopen
if (needsRestart) {
  process.send({ cmd: 'restart' });
}

if (cluster.isWorker) {
  const basePort = 8000;
  const workerPort = basePort + cluster.worker.id;

  http.createServer((req, res) => {
    res.writeHead(200);
    res.end(`Worker ${cluster.worker.id} on port ${workerPort}\n`);
  }).listen(workerPort);

  console.log(`Worker ${process.pid} listening on port ${workerPort}`);
}

// In worker process
let server;

function startServer() {
  server = http.createServer((req, res) => {
    res.writeHead(200);
    res.end('hello world\n');
  });

  server.listen(8000);
}

function gracefulShutdown() {
  console.log(`Worker ${process.pid} shutting down`);

  if (server) {
    server.close(() => {
      console.log('Server closed');
      process.exit(0);
    });

    // Force shutdown after timeout
    setTimeout(() => {
      console.error('Forced shutdown');
      process.exit(1);
    }, 10000);
  } else {
    process.exit(0);
  }
}

process.on('SIGTERM', gracefulShutdown);
process.on('SIGINT', gracefulShutdown);

startServer();