Need a better approach for assigning IPV6 address to subnets in an IPAM allocated VPC.

[mrpackethead]

This is what i'm currently doing to add IPv6 to an ec2.Vpc.

• the Ipv6 Cidr is part of a /48 allocation that is a pool in IPAM.

This works, but the moment that you change the layout of the vpc, ( such as adding new subnets, or removing them ) it falls over as the indexing will attempt to change the subnet allocations, and it very quickly becomes unworkable!

What I'd much rather do is create a Pool inside the Ipv6 pool, and then get an allocation in each ipv6 pool, and let Ipam do the assignment rather than a Index.. that way changes just work.

// Associate the CIDR with the VPC
new ec2.CfnVPCCidrBlock(this, 'Ipv6Cidr', {
  vpcId: vpc.vpcId,
  ipv6IpamPoolId: environments.sydneyIpv6Ipam.ipv6IpamPoolId,
  ipv6NetmaskLength: 56,
});


const vpcIpv6CidrBlock = vpcIpv6CidrResource.getResponseField('Vpcs.0.Ipv6CidrBlockAssociationSet.0.Ipv6CidrBlock');
const subnetIpv6CidrBlocks = core.Fn.cidr(vpcIpv6CidrBlock, 256, '64');


// provision IP address's to public and isolated subnets.
[
  ...vpc.publicSubnets,
  ...vpc.isolatedSubnets,
].forEach((subnet, i) => {
  const cfnSubnet = subnet.node.defaultChild as ec2.CfnSubnet;
  cfnSubnet.ipv6CidrBlock = core.Fn.select(i, subnetIpv6CidrBlocks);
  cfnSubnet.assignIpv6AddressOnCreation = true;
});

// this is work around, for the ipv6 allocaiton problems. 
[
  ...vpc.privateSubnets,
].forEach((subnet, i) => {
  const cfnSubnet = subnet.node.defaultChild as ec2.CfnSubnet;
  cfnSubnet.ipv6CidrBlock = core.Fn.select(i + 248, subnetIpv6CidrBlocks);
  cfnSubnet.assignIpv6AddressOnCreation = true;
});