aws-ec2: PublicSubnet does not create route table with internet gateway

[priggad]

Describe the bug

I'm trying to create a public subnet in an existing vpc. My understanding is that, unlike a private subnet, a public subnet should be created with a route table that has a route to an internet gateway but the internet gateway route does not get created.

Expected Behavior

Expecting a subnet to be created with a routing table with a route to an internet gateway.

Current Behavior

A subnet is created but it does not have a route to an internet gateway

Reproduction Steps

const vpc = ec2.Vpc.fromLookup(this, 'ExistingVPC', {
  vpcId: 'idnumber'
})

const testSubnet = new ec2.PublicSubnet(this, "TestSubnet", {
  vpcId: vpc.vpcId,
  availabilityZone: 'eu-west-2b',
  cidrBlock: '172.31.0.0/20',
  mapPublicIpOnLaunch: true,
})

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.96.2

Framework Version

No response

Node.js Version

18.17.1

OS

Fedora 38

Language

Typescript

Language Version

No response

Other information

No response

[khushail]

Hi @priggad , thanks for reaching out. I tried with existing VPC and added another subnet with the code.Subnets can currently only be created in the following availability zones: us-east-1a, us-east-1b, us-east-1c, us-east-1d, us-east-1e, us-east-1f. This is the code I ran -

    const vpc = ec2.Vpc
      .fromLookup(this, 'VPC', {
        vpcId:"vpc-01fffa360388518a5"
      });

      const testSubnet = new ec2.PublicSubnet(this, 'testSubnet', {
        vpcId: vpc.vpcId,
        availabilityZone: 'us-east-1b',
        cidrBlock: '10.0.0.0/24',
        mapPublicIpOnLaunch: true,     
        });

However, It succeeded with creating the local table for the newly created subnet but the route table to internet gateway was missing.

Marking the issue as P2.

[kevinhdz97]

Hello, I am seeing the same issue with the below code:

const vpc = new ec2.Vpc(this, 'MyVPC', {
            availabilityZones: [AvailabilityZone.US_EAST_1A, AvailabilityZone.US_EAST_1B],
            enableDnsHostnames: false,
            enableDnsSupport: false,
            ipAddresses: ec2.IpAddresses.cidr('10.0.0.0/16'),
            subnetConfiguration: [
                {
                    cidrMask: 20,
                    name: 'VPCPrivate',
                    subnetType: ec2.SubnetType.PRIVATE_ISOLATED
                }
            ],
            vpcName: 'MyVPC'
        });

        // Creates a public subnet additional to the private ones
        const publicSubnet = new ec2.PublicSubnet(this, "PublicSubnet", {
            vpcId: vpc.vpcId,
            availabilityZone: AvailabilityZone.US_EAST_1C,
            cidrBlock: '10.0.32.0/20'
        });

[priggad]

Any update on this?

[khushail]

Hi @priggad ,Apologies for the oversight earlier, I went through issue reproduction again and In CDK Code, while creating PublicSubnet, a method addNatgateway(), you can explicitly call this method to add Gateway to the subnet

aws-cdk/packages/aws-cdk-lib/aws-ec2/lib/vpc.ts

Line 2383 in 7a8ae02

public addNatGateway(eipAllocationId?: string) {

CDK Doc mentioning the same - https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.PublicSubnet.html#addwbrnatwbrgatewayeipallocationid

Let me know if this is helpful!

[github-actions]

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