Aws-cdk: Imported VPC Subnets show as Private (while they're public)

[javydekoning]

:bug: 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]

Have you tagged your subnets? CDK requires your subnets are tagged when you import them

aws-cdk:subnet-type - (Public/Private/Isolated)

[javydekoning]

No I didn't, is there any documentation on this? My search skills seem to be letting me down.

[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

[fulghum]

@reeseyc – sorry to hear you haven't had a good experience with CDK documentation. We want to fix that! Let us know if you have any specific feedback on what you liked, what you didn't, where you found gaps, etc. The more specific/concrete (i.e. in which API ref, which Construct, where in the Developer Guide, workshop, etc), the more likely we can get it fixed.

[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

[vaneek]

I find the requirement to tag subnets to be an arbitrary fix and a big impediment to adopting CDK. Often times VPCs and network related items are owned and managed by others and if every subnet in every VPC in every account has to be retro-tagged in order for a CDK app to function properly, the response will be something like, "it works with terribleform" . A big anti-pattern in my view, but hey just my 2p.