How to use locals in child modules in terraform

I've locals.tf in root module and want to use it to child modules. Directory structure is as follows:

.
├── env.tfvars
├── local.tf
├── main.tf
├── modules
│   ├── alb
│   │   ├── alb.tf
│   │   ├── output.tf
│   │   └── variable.tf
│   ├── ecr
│   │   ├── ecr.tf
│   │   ├── output.tf
│   │   └── variable.tf
│   ├── ecs
│   │   ├── ecs.tf
│   │   └── variable.tf

local.tf

locals {
  customer_env = "${var.customer_name}-${var.env}"
}

Wanted to use this locals into child modules.

modules/ecs/ecs.tf

resource "aws_ecs_cluster" "main" {
  name = "${local.customer_env}"
  tags = {
   Environment = var.env
  }
}

Tried that way but throwing an error

 Error: Reference to undeclared local value
│
│   on modules/ecs/ecs.tf line 2, in resource "aws_ecs_cluster" "main":
│    2:   name = "${local.customer_env}"
│
│ A local value with the name "customer_env" has not been declared.
╵

Child modules do not inherit variables and locals from the parent module. You have to explicitly pass them in. So, for example for your ecs module you have pass the local in:

module "ecs" {
  source = "./modules/ecs"
  customer_env = local.customer_env
}

Obviously in the ecs module you have to have the corresponding variable:

variable "customer_env" {}

And the aws_ecs_cluster.main will use the variable:

resource "aws_ecs_cluster" "main" {
  name = var.customer_env
  tags = {
   Environment = var.env
  }
}

You have to do it for all your modules.