code: function errorAppOverloaded(req, res, templateDir) {
    sendPage(res, 503, 'Too Many Users', {
      template: 'error-503-users',
      templateDir: templateDir,    
      vars: {
        message: "Sorry, but this application has exceeded its quota of concurrent users. Please try again later."
      }
    });
  }
docs: Send a 503 error response