exit event (Worker)

const worker = cluster.fork();
worker.on('exit', (code, signal) => {
  if( signal ) {
    console.log(`worker was killed by signal: ${signal}`);
  } else if( code !== 0 ) {
    console.log(`worker exited with error code: ${code}`);
  } else {
    console.log('worker success!');
  }
});