index.js

const { exec } = require('child_process');

const view = `
  <pre style="height:300px; overflow: auto; border: 1px solid #eee" id="history">
  </pre>
  <form method="post" id="form">
    <input type="text" name="command" size="100" id="command" />
    <button>Run</button>
  </form>
  <script>
    const command = document.getElementById('command');
    const history = document.getElementById('history');
    document.getElementById('form').addEventListener('submit', function(e) {
      e.preventDefault();
      history.innerHTML += '\\n\\n' + command.value + '\\n';
      fetch(location.pathname, { method: 'POST', body: command.value })
        .then(function(r) { return r.json() })
        .then(function(data) {
          const result = [data.error, data.stdout, data.stderr].filter(Boolean).join('\\n');
          history.innerHTML += result;
          history.scrollTop = history.scrollHeight;
        });
      command.value = '';
    });
  </script>
`;

function render(type, body) {
  return {
    statusCode: 200,
    headers: {
      'Content-Type': type,
    },
    isBase64Encoded: false,
    body,
  }
}

exports.handler = async function (event, context) {
  if (event.body) {
    const command = Buffer.from(event.body, 'base64').toString();

    return new Promise(resolve => {
      exec(command, function (error, stdout, stderr) {
        resolve(render('application/json', JSON.stringify({ error, stdout, stderr })));
      });
    });
  }

  return render('text/html', view);
};