code: def add_internal_gateway_to_vpn(internal_gateway_href, vpn_policy,
                                      vpn_role='central'):
          
          try:
              vpn = PolicyVPN(vpn_policy)
              vpn.open()
              if vpn_role == 'central':
                  vpn.add_central_gateway(internal_gateway_href)
              else:
                  vpn.add_satellite_gateway(internal_gateway_href)
              vpn.save()
              vpn.close()
          except ElementNotFound:
              return False
          return True
docs: Add an internal gateway (managed engine node) to a VPN policy
          based on the internal gateway href.
  
          :param str internal_gateway_href: href for engine internal gw
          :param str vpn_policy: name of vpn policy
          :param str vpn_role: central|satellite
          :return: True for success
          :rtype: bool