Manage multi-environment Terraform state with Terragrunt remote_state blocks and path_relative_to_include

Steps

1. Create a root `terragrunt.hcl` at the repository root with a `remote_state` block specifying the S3 backend, bucket, region, and a `key` using `path_relative_to_include()` to give each module a unique state path.
2. In each module subdirectory create a `terragrunt.hcl` with `include "root" { path = find_in_parent_folders() }` to inherit the root remote_state configuration.
3. Run `terragrunt init` in a module directory; Terragrunt automatically creates the S3 bucket and (if configured) the DynamoDB table if they do not exist, then runs `terraform init` with the generated backend config.
4. Use `terragrunt run-all plan` from the root to plan all modules in dependency order, respecting `dependency` blocks that wire outputs between modules.
5. Set `generate` block inside `remote_state` with `path = "backend.tf"` and `if_exists = "overwrite_terragrunt"` to have Terragrunt generate the `backend.tf` file automatically so source modules remain backend-agnostic.
6. Pin the Terragrunt version in CI using a `.tool-versions` file or a version constraint in `terragrunt.hcl` under `terraform_version_constraint` and `terragrunt_version_constraint`.