Aws_subnet returns "no matching subnets found"

Terraform
1

I have a module that I’m attempting to find AWS subnets within and then use/return. It’s called like this:

module "smurf_subnet_grp" {
   source            = "../../modules/networking/subnet_grp_per_az-test"
   vpc_id            = "${module.networking_uswe2.vpc_id}"
   azs               = "${local.az_list_uswe2}"
   private_subnets   = "${var.private_subnets_uswe2}"
}

Code for the module:

variable "azs"              { type = "list" }
variable "private_subnets"  { type = "list" }
variable "vpc_id"           {}

# ========== remove special subnets ==============

locals {
  cnt      = "${length(var.private_subnets) - 3}"
  prv_subs = "${slice(var.private_subnets, 0, local.cnt)}"
}

# ========== get subnet details ==================

data "aws_subnet" "self" {
  count         = "${length(local.prv_subs)}"
  vpc_id        = "${var.vpc_id}"
  cidr_block    = "${local.prv_subs[count.index]}"
}

# ========== get subnets by AZ ===================

locals {
  prv_subs0 = "${matchkeys(data.aws_subnet.self.*.id, data.aws_subnet.self.*.availability_zone, list(var.azs[0]))}"
  prv_subs1 = "${matchkeys(data.aws_subnet.self.*.id, data.aws_subnet.self.*.availability_zone, list(var.azs[1]))}"
  prv_subs2 = "${matchkeys(data.aws_subnet.self.*.id, data.aws_subnet.self.*.availability_zone, list(var.azs[2]))}"
}

# ========== select 1 subnet per AZ ==============

resource "random_shuffle" "prv_sub0" {
    input        = ["${local.prv_subs0}"]
    result_count = 1
}
resource "random_shuffle" "prv_sub1" {
    input        = ["${local.prv_subs1}"]
    result_count = 1
}
resource "random_shuffle" "prv_sub2" {
    input        = ["${local.prv_subs2}"]
    result_count = 1
}

# ========== put selected into 1 list ============

locals {
  prv_sub_az = [
       "${random_shuffle.prv_sub0.result}", 
       "${random_shuffle.prv_sub1.result}", 
       "${random_shuffle.prv_sub2.result}"
  ]
}

output "prv_subnet_grp" {
  value = "${local.prv_sub_az}"
}

Which throws this:

Error: Error refreshing state: 1 error occurred:
	* module.smurf_subnet_grp.data.aws_subnet.self: 6 errors occurred:
	* module.smurf_subnet_grp.data.aws_subnet.self[5]: data.aws_subnet.self.5: no matching subnet found
	* module.smurf_subnet_grp.data.aws_subnet.self[3]: data.aws_subnet.self.3: no matching subnet found
	* module.smurf_subnet_grp.data.aws_subnet.self[0]: data.aws_subnet.self.0: no matching subnet found
	* module.smurf_subnet_grp.data.aws_subnet.self[1]: data.aws_subnet.self.1: no matching subnet found
	* module.smurf_subnet_grp.data.aws_subnet.self[2]: data.aws_subnet.self.2: no matching subnet found
	* module.smurf_subnet_grp.data.aws_subnet.self[4]: data.aws_subnet.self.4: no matching subnet found

If I introduce a depends_on for the aws_subnet data provider:

data "aws_subnet" "self" {
  count         = "${length(local.prv_subs)}"
  vpc_id        = "${var.vpc_id}"
  cidr_block    = "${local.prv_subs[count.index]}"
  depends_on    = ["null_resource.module_depends_on"]
}

It’ll work as expected but then will recreate it every time.