Terraform use backend on module - amazon-s3

Question

I need to create optimize the structure of terraform.
Have on root path variables which I imported like module
/variables.tf
variable "aws_profile" { default = "default" }
variable "aws_region" { default = "us-east-1" }
After have a module folder
/ec2_instance/main.tf
module "global_vars" {
source = "../"
}
provider "aws" {
region = module.global_vars.aws_region
profile = module.global_vars.aws_profile
}
terraform {
backend "s3" {
encrypt = true
bucket = "some_bucket"
key = "path_to_statefile/terraform.tfstate"
region = "region"
profile = "profile"
}
}
module "instances_cluster" {
some actions
}
It's working, but I need to move backend and provider part to main.tf on root folder and after include like the module.
How I can do this?
I have tried to create /main.tf on root folder with backend part, but they are not working and backed writing state files locally.

Answer 1

You'd have to a bit of refactoring but these are the steps I would take
Run terraform plan in root and ec2_instance modules to verify zero changes so refactoring can begin
Comment out the backend for ec2_instance/main.tf
Place the backend from ec2_instance/main.tf into root main.tf
In the root main.tf, make a reference to ec2_instance module
Run terraform plan in root module and note the creations and deletions
For each creations and deletion pair, create a terraform state mv statement and run each
Verify the terraform plan has zero changes