Terraform — how can I properly do a string interpolation in this code?

Question

My goal is to have this output:

DB_PASSWORD="secret1"
REDIS_PASSWORD="secret1"

But I can't make it work and I'm getting this error during terraform plan.

Error: Invalid index
...
        random_password.app_secrets is object with 2 attributes

  The given key does not identify an element in this collection value.

Could you please help me how to fix this issue? Here's how my code looks like.

locals {
  require_new_secrets = toset([
    "db",
    "redis"
  ])
}

resource "random_password" "app_secrets" {
  for_each = local.require_new_secrets
  length   = 16
  special  = false
}

resource "aws_secretsmanager_secret" "app_secrets" {
  name_prefix             = "app-secrets-"
  recovery_window_in_days = 7
  tags                    = var.tags
}

resource "aws_secretsmanager_secret_version" "app_secrets" {
  secret_id     = aws_secretsmanager_secret.app_secrets.id
  secret_string = <<-EOF
    %{for x in local.require_new_secrets}
    ${upper("{x}_PASSWORD")}=${random_password.app_secrets["{x}"].result}
    %{endfor}
  EOF
}

Thanks in advance!

Answer 1

As mentioned in my comment, the interpolation syntax in Terraform requires you to add a $ in front of any variable where substitution is required. For your code to work it is enough to add a $ in front of both {x} placeholders:

resource "aws_secretsmanager_secret_version" "app_secrets" {
  secret_id     = aws_secretsmanager_secret.app_secrets.id
  secret_string = <<-EOF
    %{for x in local.require_new_secrets}
    ${upper("${x}_PASSWORD")}=${random_password.app_secrets["${x}"].result}
    %{endfor}
  EOF
}

More on interpolation syntax can be found in [1] and the example looks very similar to what you are trying to do.

---

[1] https://www.terraform.io/language/expressions/strings#directives