Terraform 0.12 - For each subnet-id in array, get cidr_block

Question

I have a list of subnets IDs and I want to get an array of the cidr_blocks associated to each subnet.

variable "aws_subnet_ids" {
  type = list(string)
  default = ["subnet-aaaaaaaa","subnet-bbbbbbbb"]
}

desired_output = ['10.0.1.0/24', '10.0.2.0/24']

I've been fiddling around with for loops and count data for a quite a while for what should be a really simple problem. But I'm having a hard time finding an appropriate way to actually do this.

This seemed like a decent example to work off of, but you can't actually use a for_each in a data source off a list of strings. https://www.terraform.io/docs/providers/aws/d/subnet_ids.html

data "aws_subnet" "example" {
  for_each = var.aws_subnet_ids
  cidr_blocks       = each.cidr_block
}

output "subnet_cidr_blocks" {
  value = [for s in data.aws_subnet.example : s.cidr_block]
}

Answer 1

data "aws_subnet" "subnets" {
  for_each = toset(var.aws_subnet_ids)
  id       = each.value
}

locals {
  cidr_blocks = [
    for subnet in data.aws_subnet.subnets :
      subnet.cidr_block
    ]

  cidr_blocks_rendered = [
    for cidr_block in local.cidr_blocks :
     {
       from_port   = 6443,
       to_port     = 6443,
       protocol    = "tcp",
       cidr_blocks = cidr_block
     }
  ]
}

output "output1-1" {
  value = local.cidr_blocks_rendered
}

This is what ultimately I needed.