Add CDK Example: How to do a lookup by subnet group name

[takashi-uchida]

Describe the feature

The subnet group name can be used to refer to the intended subnet quickly.

Use Case

Many samples reference subnets created in the VPC stack, such as ec2.SubnetSelection is handled by a subnet type call, list, or import function.
However, in actual requirements, many requirements cannot be divided by subnet type, such as subnets for network firewalls, transit gateways, and so on.

Proposed Solution

subnet_group_name_tag and cdk.json

Other Information

No response

Acknowledgements

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

Language

Python

[rushali-aws]

@takashi-uchida , I checked that in subnet Selection we can use subnetGroupName. During my testing , I noticed that CDK uses the tag "aws-cdk:subnet-name" for subnetGroupName.

I added the tag 'aws-cdk:subnet-name' to my subnets in a VPC with value 'Private-tag' and used the below code :

vpc = ec2.Vpc.from_lookup(self, "MyVpc",
            vpc_id='vpc-XXXXXXXXX'
        )

        subnet_ids = vpc.select_subnets(
            subnet_group_name="Private-tag"
        ).subnet_ids

        for subnet_id in subnet_ids:
            print("Subnet Ids: " + subnet_id)

I was able to check in my cdk.context.json file , under subnetGroups , there were subnets with this tag. And in the output of " print("Subnet Ids: " + subnet_id)" , I could see my subnets on which I added the tag.

You can add tag "aws-cdk:subnet-name" on the required subnets with same value and then use above way to select them by subnetGroupName.

[takashi-uchida]

Thank you. I have been handling it as follows.

self.vpc = ec2.Vpc(
            self,
            "vpc",
            vpc_name=f"vpc-{project_name}",
            ip_addresses=ec2.IpAddresses.cidr(vpc_cidr),
            max_azs=3,
            subnet_configuration=[
                ec2.SubnetConfiguration(
                    name=f"public-{project_name}",
                    cidr_mask=24,
                    subnet_type=ec2.SubnetType.PUBLIC,
                ),
                ec2.SubnetConfiguration(
                    name=f"private-{project_name}",
                    cidr_mask=24,
                    subnet_type=ec2.SubnetType.PRIVATE_WITH_EGRESS,
                ),
                ec2.SubnetConfiguration(
                    name=f"isolated-{project_name}",
                    cidr_mask=24,
                    subnet_type=ec2.SubnetType.PRIVATE_ISOLATED,
                ),
                ec2.SubnetConfiguration(
                    name=f"tgw-{project_name}",
                    cidr_mask=24,
                    subnet_type=ec2.SubnetType.PRIVATE_ISOLATED,
                ),
            ],
        )

vpc = ec2.Vpc.from_lookup(
            self, "vpc", vpc_name=vpc_name, subnet_group_name_tag="aws-cdk:subnet-name"
        )


vpc_subnets=ec2.SubnetSelection(
                subnet_group_name="private-{project_name}"),