Hardcoded newbits value in cidrsubnet Function Causing Scalability Issues

[Vinoth-S15]

Is your request related to a problem? Please describe.

The current code uses a hardcoded value for the newbits argument in the cidrsubnet function, which is not scalable and is causing issues when creating a VPC with non-/56 ranges.

For example, if the VPC IPv6 CIDR block is /60, the code attempts to create a subnet with /68, which is an unacceptable value.

Describe the solution you'd like.

To improve scalability, I propose introducing a new variable that provides the flexibility to select subnet sizes based on the VPC's IPv6 CIDR block size.

Resource: aws_subnet

Current argument:

ipv6_cidr_block = var.enable_ipv6 && length(var.private_subnet_ipv6_prefixes) > 0

Proposed solution:

ipv6_cidr_block = var.enable_ipv6 && length(var.public_subnet_ipv6_prefixes) > 0 ? cidrsubnet(aws_vpc.this[0].ipv6_cidr_block, var.cidr_subnet_newbits, var.public_subnet_ipv6_prefixes[count.index]) : null

This change allows for more flexibility in subnet size selection by using a variable for newbits, making the code adaptable to different VPC IPv6 CIDR sizes.

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