(aws-ec2): RouterType.GATEWAY comment is misleading - it also supports Virtual Private Gateway

Describe the feature

The doc comment on RouterType.GATEWAY only mentions "Internet Gateway", but the underlying CloudFormation GatewayId property actually accepts both an Internet Gateway ID and a Virtual Private Gateway ID. This makes the API misleading for users who want to add a route targeting a VGW.

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-ec2/lib/vpc.ts#L2402-L2405

CloudFormation reference: The AWS::EC2::Route documentation states that GatewayId is:

The ID of an internet gateway or virtual private gateway attached to your VPC.

Use Case

When defining a route on a subnet using addRoute() (or creating a CfnRoute via the higher-level API), RouterType is used to specify the target router. For example, when connecting an on-premises network to a VPC via a Virtual Private Gateway, users need to add a route that targets the VGW

(vpc.privateSubnets[0] as ec2.Subnet).addRoute('VgwRoute', {
  routerId: vpnGateway.gatewayId,
  routerType: ec2.RouterType.GATEWAY, // ← works for VGW too, but the comment says only "Internet Gateway"
  destinationCidrBlock: '10.1.0.0/16',
});

Proposed Solution

export enum RouterType {
  /**
   * Internet Gateway or Virtual Private Gateway
   */
  GATEWAY = 'Gateway',
...
}

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

AWS CDK Library version (aws-cdk-lib)

aws-cdk-lib@2.250.0

AWS CDK CLI version

2.1115.1 (build e979d8d)

Environment details (OS name and version, etc.)

OS wsl Ubuntu24.04