cidrsubnet magic

main.tf

module "anvil" {
  source = "./subnets"
  cidr_block = "10.192.12.0/22"
  subnet_mask = 24
}

output "size" {
  value = "${module.anvil.size}"
}

output "subnets" {
  value = "${module.anvil.subnets}"
}

subnets-main.tf

variable "cidr_block" {
  
}

variable "subnet_mask" {
  default = 24
}


locals {
  child_subnet_mask = "${var.subnet_mask - (element(split("/", var.cidr_block), 1))}"
}

output "size" {
  value = "${local.child_subnet_mask}"
}

output "subnets" {
  value = "${list(
    cidrsubnet(var.cidr_block, local.child_subnet_mask, 0),
    cidrsubnet(var.cidr_block, local.child_subnet_mask, 1),
    cidrsubnet(var.cidr_block, local.child_subnet_mask, 2)
  )}"
}

change "module.anvil.anvil_subnet" to "module.anvil.subnets". Thanks