Terraform Try for Argument existence

Question

We have defined variables for a given module. This is a sample

    variable "kv_name_solution" { }
    variable "kv_name_seqnr" { }
    variable "kv_name_purpose" { }
...    
    variable "location_name" { default = "Europe" }
    variable "location_tier" { default = "Primary" }  
    variable "rg_name_solution" { default = "edw"}
    variable "rg_name_seqnr" { default = "001"}

In our tfvars plenty of kv are prepared. So in a template we use this code

module "kv_create" {
  for_each = var.resources_kv
  source = "../../_modules/security/kv_create"

  kv_name_solution        = each.value["kv_name_solution"]
  kv_name_seqnr           = each.value["kv_name_seqnr"]
  kv_name_purpose         = each.value["kv_name_purpose"]
...
  location_name        = each.value["location_name"]
  location_tier        = each.value["location_tier"]
  rg_name_solution     = each.value["rg_name_solution"]
  rg_name_seqnr        = each.value["rg_name_seqnr"]
}

But, I'm trying to find a way that when in the tfvars for example the rg_name_solution and rg_name_seqnr are omitted the code in the for_each still works. Have been searching with try, but couldn't get it right so far.

Because location_name = try(each.value["location_name"], null) seems to cancel my default set on the variable.

Any suggestions ?

These are the 'complete files'

terraform.tfvars

rg_resources = {
        "edw-common" = {

                rg_name_solution        = "edw"
                rg_name_seqnr           = "001"

                rg_location_name        = "Europe"
                rg_location_tier        = "Primary"
        }
}

kv_resources = {
        "adf-001" = {
                kv_name_solution        = "edw"
                kv_name_seqnr           = "001"
                kv_name_purpose         = "adfxx"

                }
}

main.tf

....
module "provision_keyvaults" {
  count     = (var.MODULE == "KV") || ((var.MODULE == "ALL" && var.APPLY == "false")) ? 1 : 0
  source    = "./_templates/kv"

  resources_kv = var.kv_resources
}
....

template\kv\main.tf

module "kv_create" {
  for_each = var.resources_kv
  source = "../../_modules/security/kv_create"

  kv_location_name        = try(each.value["kv_location_name"],null)
  kv_location_tier        = try(each.value["kv_location_tier"],null)

  kv_name_solution        = each.value["kv_name_solution"]
  kv_name_seqnr           = each.value["kv_name_seqnr"]
  kv_name_purpose         = each.value["kv_name_purpose"]

  rg_name_solution        = try(each.value["rg_name_solution"],null)
  rg_name_seqnr           = try(each.value["rg_name_seqnr"],null)

 }

template\kv\variables.tf

variable "resources_kv" { }

_modules\kv_create\variables.tf

variable "kv_location_name" {
                              default = "Europe"
                            }
variable "kv_location_tier" {
                              default = "Primary"
                            }

variable "kv_name_solution" { }
variable "kv_name_seqnr" { }
variable "kv_name_purpose" { }

variable "rg_name_solution" {
                              default = "edw"
                            }
variable "rg_name_seqnr" {
                           default = "001"
                         }

_modules\kv_create\main.tf

module "subscription" {
  source = "../../general/subscription_getdetails"
}

module "kv_location" {
  source = "../../general/location_getdetails"
  location_name = var.kv_location_name
  location_tier = var.kv_location_tier
}

module "resourcegroup" {
  source = "../../general/rg_getdetails"
  rg_name_solution = var.rg_name_solution
  rg_name_seqnr    = var.rg_name_seqnr
}

data "azurerm_client_config" "current" {}

resource "azurerm_key_vault" "kv" {
  count                       = var.kv_provision ? 1 : 0

  name                        = "kv-${module.kv_location.sitecode}-${module.subscription.environment}-${var.kv_name_solution}-${var.kv_name_seqnr}-${var.kv_name_purpose}"

....

  resource_group_name         = module.resourcegroup.rg.name
  location                    = module.kv_location.azure
...
}

And bottom line, the error

╷
│ Error: Invalid template interpolation value
│ 
│   on _modules/general/rg_getdetails/main.tf line 18, in data "azurerm_resource_group" "rg":
│   18:   name = "rg-${module.subscription.environment}-${var.rg_name_solution}-${var.rg_name_seqnr}"
│     ├────────────────
│     │ var.rg_name_solution is null
│ 
│ The expression result is null. Cannot include a null value in a string
│ template.
╵

Answer 1

I would just use lookup to provide a default value if not explicitly given. For example:

  kv_name_solution        = lookup(each.value, "kv_name_solution", var.kv_name_solution)
  kv_name_seqnr           = lookup(each.value, "kv_name_seqnr", var.kv_name_seqnr)
  kv_name_purpose         = lookup(each.value, "kv_name_purpose", var.kv_name_purpose)