Terraform interactive input doesn't work with the root module - terraform

Question

Terraform Version
Terraform v1.1.2
on windows_amd64
Terraform Configuration Files
child_module1.tf(C1):
# Create Resource Group
resource "aws_resourcegroups_group" "resourcegroups_group" {
name = "test"
resource_query {
query = <<JSON
{
"ResourceTypeFilters": [
"AWS::EC2::Instance"
],
"TagFilters": [
{
"Key": "project",
"Values": ["${var.ProjectName}"]
}
]
}
JSON
}
}
child_module1_variables.tf:
########
variable "ProjectName" {
type = string
description = "This name would be prefixed with the cluster names."
}
Now call this child module in another child module**(C2)**:
child_module2.tf:
module "prepare_aws_cloud" {
source = "./modules/aws/prepare_cloud_copy"
ProjectName = "${var.test.ProjectName}"
}
child_module2_variables.tf:
variable "test" {
type = object({
ProjectName = string
})
}
Now I create a root module(R1)** which calls the child_module2.tf:**
terraform {
backend "local" {
}
}
module "test_deploy" {
source = "D:\\REPO\\installer_v2.2.22.1\\installer\\aws"
test = {
#ProjectName = ""
}
}
So the dependency is as follows:
R1 calls >> C2 calls >> C1
ERROR
PS D:\tkgTest> terraform apply -input=true
╷
│ Error: Invalid value for module argument
│
│ on testing.tf line 21, in module "test_deploy":
│ 21: test= {
│ 22: #ProjectName = ""
│ 23: }
│
│ The given value is not suitable for child module variable "test" defined at .terraform\modules\test_deploy\variables.tf:108,1-15: attribute "ProjectName" is required.
Expected Behavior
I would have expected that the user input would be taken interactively by the console as I am passing the -input=true flag but it doesn't seem to work.

Answer 1

The interactive prompts for input variables are intended only to help with getting started with Terraform (e.g. following a simple tutorial) and so they are limited in the scope of what they support. The typical way to set root module input variables for routine use is to either create a .tfvars file and pass it to Terraform with -var-file or to set a variable directly using -var.
Note also that only root module input variables can be set directly as part of the planning options. Any child module variables are defined exclusively by the expressions written in the module block, and so if you want to be able to set a child module's input variable on a per-run basis you'll need to also declare it as a root module variable and then pass it through to the child module.
For example, in the root module:
variable "test" {
type = object({
ProjectName = string
})
}
module "test_deploy" {
source = "./installer/aws"
test = var.test
}
You can then create an example.tfvars file with the following to set a value for the variable:
test = {
ProjectName = "example"
}
Specify that file when you run Terraform:
terraform apply -var-file=example.tfvars
If you will always set the same values then you can avoid the need for the extra option by naming your file example.auto.tfvars and placing it in the same directory where you will run Terraform. Terraform will load .auto.tfvars files automatically without any explicit -var-file option.