[aws-elasticloadbalancingv2] Add support for SubnetMapping to Network Load Balancer

[michaelwiles]

Add Subnet mappings to the Network Load Balancer construct

Use Case

We have a network load balancer and we need it on a static ip thus we hook up an elastic ip to this network load balancer.

This is possible via the console and it also seems possible via the SubnetMapping property on network load balancer in cloudformation.

Proposed Solution

To add that subnet mapping construct as a property on the NetworkLoadBalancer construct.

Other

I suspect that in the mean time I can use the CfnLoadBalancer either as the primary construct or fetch it and change it after creation of the cdk network load balancer.

Not sure if I should try this or focus on adding the mapping to the network load balancer...

There is already an available SubnetMappingProperty which I'd assume we'd replicate in the primary world (it's in the Cfn world and thus potentially not stable).

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

---

This is a 🚀 Feature Request

[michaelwiles]

hmmm not sure if it's even worth it...

This does the job:

load_balancer = elbv2.NetworkLoadBalancer(
    self, 'LoadBalancer', vpc=vpc, vpc_subnets=SubnetSelection(subnets=[vpc.public_subnets[0]])
)
cfn_load_balancder: CfnLoadBalancer = load_balancer.node.default_child

subnet_mapping = CfnLoadBalancer.SubnetMappingProperty(
    subnet_id=vpc.public_subnets[0].subnet_id, allocation_id='eipalloc-XXXXYYYYxxxxyyyy'
)
cfn_load_balancder.subnet_mappings = [subnet_mapping]

[flemjame-at-amazon]

Also interested in this for the ability to specify the private IPv4 of a NetworkLoadBalancer - see PrivateIPv4Address

[cfclrk]

@michaelwiles Thanks for the example, it helped me! It doesn't quite work as written though:

You can specify either subnets or subnet mappings, not both

This error is an example of why it's nice to have higher-level constructs for these kinds of things.

[cfclrk]

See also: #7424

[mr-brobot]

@cfclrk I encountered the same error and this worked for me.

elastic_ip = CfnEIP(self, "EIP")

network_load_balancer = NetworkLoadBalancer(
    self,
    "NetworkLoadBalancer",
    vpc=cluster.vpc,
    internet_facing=True,
)

cfn_nlb = network_load_balancer.node.default_child

subnet_mapping = CfnLoadBalancer.SubnetMappingProperty(
    subnet_id=cluster.vpc.public_subnets[0].subnet_id,
    allocation_id=elastic_ip.attr_allocation_id,
)

cfn_nlb.subnet_mappings = [subnet_mapping]

# i think the higher-level NetworkLoadBalancer construct sets subnets on the lower-level CfnLoadBalancer construct
# clearing subnets on the lower-level construct allowed me to add the subnet mapping without issue
cfn_nlb.subnets = None

Credit to @michaelwiles for the solution!

[forsberg]

Many thanks to @josh-wiley for the working example. Here extended to also set a fixed IPv6 address on a dualstack NLB:

eip = CfnEIP(self, "ElasticIP")

self.nlb = NetworkLoadBalancer(
    self,
    "LoadBalancer",
    vpc=self.vpc,
    internet_facing=True
)
cfn_lb: CfnLoadBalancer = self.nlb.node.default_child
cfn_lb.ip_address_type = "dualstack"

cfn_subnet: CfnSubnet = self.vpc.public_subnets[0].node.default_child
ipv6_network = Fn.select(0, cfn_subnet.attr_ipv6_cidr_blocks)

ipv6_prefix = Fn.select(0, Fn.split("::", ipv6_network))
# The answer to what the last part of the IPv6 address should be is obviously 42
ipv6_addr = Fn.join("::", [ipv6_prefix, "42"])

subnet_mapping = CfnLoadBalancer.SubnetMappingProperty(
    subnet_id=self.vpc.public_subnets[0].subnet_id,
    allocation_id=eip.attr_allocation_id,
    i_pv6_address=ipv6_addr
)

cfn_lb.subnet_mappings = [subnet_mapping]
cfn_lb.subnets = None

[bkeifer]

I'm trying to set a pair of Elastic IPs as the public facing addresses for a NetworkLoadBalancer object and running into issues. The console.log("CFN NLB"); line never executes because the load balancer definition throws the following error:

There are no 'Public' subnet groups in this VPC. Available types:

Subprocess exited with error 1

Code:

    const subnet1 = Subnet.fromSubnetId(this, 'subnet1', 'subnet-xxxxx4c499ef987fe');
    const subnet2 = Subnet.fromSubnetId(this, 'subnet2', 'subnet-xxxxx2d40a27dd263');

    console.log("Load Balancer...");
    this.loadBalancer = new NetworkLoadBalancer(this, 'dnsLB', {
      vpc: assets.vpc,
      internetFacing: true,
    });

    console.log("CFN NLB");
    this.cfnNLB = this.loadBalancer.node.defaultChild as CfnLoadBalancer;

    console.log("Mappings");
    const subnetMapping1: CfnLoadBalancer.SubnetMappingProperty = {
      subnetId: 'subnet-xxxxx4c499ef987fe',
      allocationId: assets.elasticIp1.attrAllocationId,
    }
    const subnetMapping2: CfnLoadBalancer.SubnetMappingProperty = {
      subnetId: 'subnet-xxxxx2d40a27dd263',
      allocationId: assets.elasticIp2.attrAllocationId,
    }

    console.log("Mapping assignment");
    this.cfnNLB.subnetMappings = [subnetMapping1, subnetMapping2];

I've found references to CDK wanting a tag of aws-cdk:subnet-type with a value of Public and added that tag to our public subnets, but the error remains unchanged.