Why isn't terraform interpolation working? - terraform

Question

So my goal is to have write a terraform code to deploy 3 resource groups in AZ dev, uat and prod with each having the following resources.
SQL Database
Key Vault
variable.tf
variable "resource_group_name" {
description = "deafault resource group"
type = list (string)
default = ["Test-dev","Test-uat","Test-prod"]
}
variable "storage_account_name" {
description = "name for storage account"
default = "test-storageact"
}
main.tf
resource "azurerm_resource_group" "resgrp" {
for_each = toset(var.resource_group_name)
name = "${var.resource_group_name}-rg-${each.value}"
location = var.location
tags = {
"Environment" = "${var.env}-${each.value}"
}
}
resource "azurerm_storage_account" "storageact" {
for_each = toset(var.resource_group_name)
name = "${var.storage_account_name}-${each.value}"
resource_group_name = azurerm_resource_group.resgrp["${each.value}"].location
location = azurerm_resource_group.resgrp["${each.value}"].name
account_tier = "Standard"
account_replication_type = "LRS"
tags = {
"Environment" = "${var.env}-${each.value}"
}
}
error message
│ Error: Invalid template interpolation value
│
│ on main.tf line 3, in resource "azurerm_resource_group" "resgrp":
│ 3: name = "${var.resource_group_name}-rg-${each.value}"
│ ├────────────────
│ │ var.resource_group_name is list of string with 3 elements
│
│ on main.tf line 6, in resource "azurerm_resource_group" "resgrp":
│ 6: "Environment" = "${var.env}-${each.value}"
│ ├────────────────
│ │ var.env is map of string with 3 elements
│
│ Cannot include the given value in a string template: string required.
╵
Operation failed: failed running terraform plan (exit 1)
please any help will be greatly appreciated.
i tried using type = map(string) in the variable but still gave me an error.

Answer 1

There are a few problems with the code.
var.resource_group_name is a list containing 3 string elements (by default), and thus the error: var.resource_group_name is list of string with 3 elements explains the problem, and is illustrated below.
The var.env is a map consisting of 3 elements and also being used as a string and fails for the same reason.
resource "azurerm_resource_group" "resgrp" {
for_each = toset(var.resource_group_name)
# var.resource_group_name is actually a list, but it's being
# used as a string here, which will fail.
name = "${var.resource_group_name}-rg-${each.value}"
location = var.location
tags = {
"Environment" = "${var.env}-${each.value}"
}
}
You probably instead want:
resource "azurerm_resource_group" "resgrp" {
for_each = toset(var.resource_group_name)
name = "${each.value}-rg"
location = var.location
tags = {
"Environment" = "${each.value}"
}
}
Additionally, as an alternative to the approach of putting multiple environments in a single resource construct, consider using modules to create reusable infrastructure for your resources and then calling each module for the environment that you're using, this is a best practice when implementing duplicate or near-duplicate infrastructure across multiple environments and allows you some flexibility with naming conventions and other parameters that would differ based upon the environment.
Rough example:
module "test-dev" {
source = "../modules/infrastructure"
environment = "Test-dev"
vm_count = 1
}
module "test-uat" {
source = "../modules/infrastructure"
environment = "Test-dev"
vm_count = 3
}
module "test-prod" {
source = "../modules/infrastructure"
environment = "Test-prod"
account_tier = "Premium"
vm_count = 6
}