const dispatcher = new Pool('http://127.0.0.1:8090' /* an 4worker nginx */, {
  pipelining: 30,
  connections: 100,
});

const proxy = http.createServer((req, res) => {
  dispatcher.request({ // the constructor of RequestHandler in undici/lib/api/api-request.js
    method: req.method,
    path: req.url,
    headers: req.headers,
    body: req,
  }, (err, { statusCode, headers, body /** a Readable */ }) => {
    if (err) {
      throw err
    }
    res.writeHead(statusCode, headers);
     pipe(body, res);
  });
});

function pipe(src, dst) {
  src.on('readable', () => {
    let chunk;
    while (null !== (chunk = src.read(65536))) {
      dst.write(chunk);
    }
  });
  src.on('end', () => {
    dst.end()
  });
}