code: def create_route(self, route_table_id, destination_cidr_block, gateway_id=None, instance_id=None):
          
          params = {
              'RouteTableId': route_table_id,
              'DestinationCidrBlock': destination_cidr_block
          }
  
          if gateway_id is not None:
              params['GatewayId'] = gateway_id
          elif instance_id is not None:
              params['InstanceId'] = instance_id
  
          return self.get_status('CreateRoute', params)
docs: Creates a new route in the route table within a VPC. The route's target
          can be either a gateway attached to the VPC or a NAT instance in the
          VPC.
  
          :type route_table_id: str
          :param route_table_id: The ID of the route table for the route.
  
          :type destination_cidr_block: str
          :param destination_cidr_block: The CIDR address block used for the
                                         destination match.
  
          :type gateway_id: str
          :param gateway_id: The ID of the gateway attached to your VPC.
  
          :type instance_id: str
          :param instance_id: The ID of a NAT instance in your VPC.
  
          :rtype: bool
          :return: True if successful