aws-cdk: VPC with only private subnet fails with error

❓ General Issue

The Question

Because creating a VPC with default settings creates a public and private subnets that default to a NAT gateway for each public subnet, i am running out of EIP. My application doesnt even need a NAT gateways, its just an app that uses dax to connect to dynamodb. Anyways, i tried creating a vpc with just private subnet and add dynamo as a gateway endpoint:

const daxVpc = new Vpc(this, 'daxVpc', {
      cidr: Vpc.DEFAULT_CIDR_RANGE,
      subnetConfiguration: [{
        subnetType: SubnetType.PRIVATE,
        name: defaultSubnetName(SubnetType.PRIVATE)
      }],
      gatewayEndpoints: {
        DYNAMODB: {
          service: GatewayVpcEndpointAwsService.DYNAMODB
        }
      }
    });

but it errors out during deployment:

8/31 | 16:24:34 | CREATE_IN_PROGRESS   | AWS::EC2::Subnet                      | daxVpc/IsolatedSubnet1/Subnet (daxVpcIsolatedSubnet1SubnetA090FC82) Resource creation Initiated
  8/31 | 16:24:34 | CREATE_IN_PROGRESS   | AWS::EC2::Subnet                      | daxVpc/IsolatedSubnet2/Subnet (daxVpcIsolatedSubnet2Subnet469D29C8) Resource creation Initiated
  9/31 | 16:24:34 | CREATE_COMPLETE      | AWS::EC2::RouteTable                  | daxVpc/IsolatedSubnet2/RouteTable (daxVpcIsolatedSubnet2RouteTableE102F846) 
 10/31 | 16:24:34 | CREATE_COMPLETE      | AWS::EC2::RouteTable                  | daxVpc/IsolatedSubnet1/RouteTable (daxVpcIsolatedSubnet1RouteTable5B90AC7F) 
 11/31 | 16:24:36 | CREATE_FAILED        | AWS::EC2::Route                       | daxVpc/IsolatedSubnet1/DefaultRoute (daxVpcIsolatedSubnet1DefaultRoute54F632D7) Exactly one of [EgressOnlyInternetGatewayId, InstanceId, NatGatewayId, TransitGatewayId, GatewayId, VpcPeeringConnectionId, NetworkInterfaceId] must be specified and not empty

What configuration am i missing ??

Environment

• CDK CLI Version: 1.3.0
• Module Version: 1.3.0
• OS:
• Language: TypeScript

Other information