Passing Terraform variables between Modules within Modules?

I have an issue I have gotten stuck on building a module from the Kubespray project.

I have the following folder structure:

terraform/
modules/
   kubespray/
      modules/
         compute/
         ips/
         network/
      main.tf
      variables.tf
roles/
    kubespray/
        terraform_setup/
             main.tf

Within the kubespray/main.tf module there are variables being passed around:

module "ips" {
  source = "./modules/ips"

  number_of_k8s_masters         = "${var.number_of_k8s_masters}"
  number_of_k8s_masters_no_etcd = "${var.number_of_k8s_masters_no_etcd}"
  number_of_k8s_nodes           = "${var.number_of_k8s_nodes}"
  floatingip_pool               = "${var.floatingip_pool}"
  number_of_bastions            = "${var.number_of_bastions}"
  external_net                  = "${var.external_net}"
  network_name                  = "${var.network_name}"
  router_id                     = "${module.network.router_id}"
}

module "compute" {
  source = "./modules/compute"
  ...
  k8s_master_fips                              = "${module.ips.k8s_master_fips}"
  k8s_master_no_etcd_fips                      = "${module.ips.k8s_master_no_etcd_fips}"
  k8s_node_fips                                = "${module.ips.k8s_node_fips}"
  bastion_fips                                 = "${module.ips.bastion_fips}"
  ...
}
output "private_subnet_id" {
  value = "${module.network.subnet_id}"
}

output "floating_network_id" {
  value = "${var.external_net}"
}

output "router_id" {
  value = "${module.network.router_id}"
}

output "k8s_master_fips" {
  value = "${concat(module.ips.k8s_master_fips, module.ips.k8s_master_no_etcd_fips)}"
}

output "k8s_node_fips" {
  value = "${module.ips.k8s_node_fips}"
}

output "bastion_fips" {
  value = "${module.ips.bastion_fips}"
}

If I run my terraform init/apply from inside the submodule in modules/kubespray/ It works fine

If I run from my role/kubespray that has

module "kubespray" {
  source    = "../../../modules/kubespray"
  providers = {
    openstack.src = openstack
  }
}

it fails with

Error: Invalid index

on ../../../modules/kubespray/modules/compute/main.tf line 670, in resource "openstack_compute_floatingip_associate_v2" "k8s_node": 670: floating_ip = "${var.k8s_node_fips[count.index]}" |---------------- | count.index is 0 | var.k8s_node_fips is empty list of dynamic

Help would be extremely appreicated

When you run terraform, the directory becomes an implicit "root module". As it's explained in the Input Variables documentation, root modules can access TF inputs from the CLI or environment, but all other called modules need to have these passed in.

I'm assuming what's happening could be that your ~kubespray/variables.tf input variables have default values assigned which are taking effect. If that's the case, then these should be copied over to ~terraform_setup/variables.tf and passed into the calling module:

module "kubespray" {
  source    = "../../../modules/kubespray"
  providers = {
    openstack.src = openstack
  }
}