Imported VPC Subnets show as Private (while they're public)

🐛 Bug Report

What is the problem?

When I import a VPC with a single public subnet, CDK says there are no Public Subnets. Specifically: There are no 'Public' subnets in this VPC. Use a different VPC subnet selection.

I’m using this to deploy a public ALB.

Reproduction Steps

Here’s my route-table:

{
    "RouteTables": [
        {
            "Associations": [
                {
                    "Main": true,
                    "RouteTableAssociationId": "rtbassoc-xxxxxx",
                    "RouteTableId": "rtb-xxxxxx"
                },
                {
                    "Main": false,
                    "RouteTableAssociationId": "rtbassoc-xxxxxx",
                    "RouteTableId": "rtb-xxxxxx",
                    "SubnetId": "subnet-xxxxxx"
                }
            ],
            "PropagatingVgws": [],
            "RouteTableId": "rtb-xxxxxx",
            "Routes": [
                {
                    "DestinationCidrBlock": "10.0.2.0/26",
                    "Origin": "CreateRoute",
                    "State": "active",
                    "VpcPeeringConnectionId": "pcx-xxxxxx"
                },
                {
                    "DestinationCidrBlock": "10.0.1.0/24",
                    "GatewayId": "local",
                    "Origin": "CreateRouteTable",
                    "State": "active"
                },
                {
                    "DestinationCidrBlock": "0.0.0.0/0",
                    "GatewayId": "igw-xxxxxx",
                    "Origin": "CreateRoute",
                    "State": "active"
                }
            ],
            "Tags": [],
            "VpcId": "vpc-xxxxxx",
            "OwnerId": "xxxxxx"
        }
    ]
}

Stack:

export class SampleStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, { env: { account: "xxxxxx", region: "eu-west-1" } });

    const vpcpub = ec2.Vpc.fromLookup(this, "pub", {
      vpcId: "vpc-xxxxx"
    });

    const lb = new elb.ApplicationLoadBalancer(this, "alb", {
      vpc: vpcpub,
      internetFacing: true
    });

    const listener = lb.addListener("pub", { port: 80, open: true });

    listener.addTargets("ecs", {
      port: 8000,
      targets: []
    });

    new cdk.CfnOutput(this, "LoadBalancerDNS", {
      value: lb.loadBalancerDnsName
    });
  }
}

Verbose Log

CDK_CONTEXT_JSON: 
{
   "vpc-provider:account=xxxxxx:filter.vpc-id=vpc-xxxxxx:region=eu-west-1":{
      "vpcId":"vpc-xxxxxx",
      "availabilityZones":[
         "eu-west-1a"
      ],
      "privateSubnetIds":[
         "subnet-xxxxxx"
      ],
      "privateSubnetNames":[
         "Private"
      ],
      "privateSubnetRouteTableIds":[
         "rtb-xxxxxx"
      ]
   }
   "aws:cdk:enable-path-metadata":true,
   "aws:cdk:enable-asset-metadata":true
}

Environment

• CDK CLI Version: 1.4.0
• Module Version: 1.4.0
• OS: MacOS 10.14.6
• Language: TypeScript

[reeseyc]

@fulghum Hi Jason; we are facing 2 major challenges with CDK documentation. Firstly (and most challenging) is the lack of examples (especially working examples). Secondly, although the API documentation is actually pretty good, the nuances of using CDK are not documented. For instance, take the VPCfromlookup method - where does it say in the documentation that the subnets need to be tagged for this to work properly (as per above)? Happy to be corrected if i am not looking in the right place

[reeseyc]

Hahahaa dude if you want documentation don’t use CDK. Your subnets need to be tagged to load them Key name is aws-cdk then the subnet type in the field. (Public/Private/Isolated)

there is some information about it in this bug report (which is how i figured it out).

https://github.com/aws/aws-cdk/issues/3407