terraform is logical but not natural

The subject kind of says it all. If you can use environment variables (and you can and probably should) in terraform with the invocation/usage of TF_VAR_environment_variable_name, why in the ever loving world can you not do the same in modules (or sub-modules as I think of them)? Apparently environment variables don't propagate into the submodules.

So, you basically "re-declare" when you define/invoke the submodule. See: https://stackoverflow.com/questions/53853790/terraform-how-to-pass-environment-variables-to-sub-modules-in-terraform

In my case, I'm building "N" VMs in submodules and there is a "vms.tf" that has the "module "NAME" {} invocation (and of course there are "N" of these) so I had to do something like:

module "FIRST" {variableone = var.variableone}

.

.

.

module "NTH" {variableone = var.variableone}

"N" times and then at the top level (main.tf or variables.tf) something like:

variable "variableone" {
  description = "Cascade environment variable in terraform"
  default = ""

}

and then
export variableone="myvaluegoeshere"

in my environment.