Terraform Modules

In modern cloud infrastructure, you rarely write every resource from scratch. Instead, platform teams rely on verified, reusable Terraform Modules (either from the public Terraform Registry or private corporate registries).

Watt TF integrates seamlessly with Terraform Modules. Since module calls are just JSON objects under the hood of .tf.json, your blueprints can dynamically stamp out module invocations based on your input data.

1. The Input Data (input.yaml)

Imagine your engineering teams need to provision static websites with Amazon S3 and CloudFront. They just define the core parameters of their sites:

team: marketing
websites:
  - name: corporate-blog
    domain: blog.mycompany.com
    price_class: PriceClass_100 # US and Europe only (cost-efficient)
  - name: documentation
    domain: docs.mycompany.com
    price_class: PriceClass_All # Global distribution

2. The Blueprint (blueprint.yaml)

Instead of writing complex HCL wrapping logic, your blueprint uses for_each to iterate over the array of websites and invokes a verified CloudFront/S3 module for each entry.

transform:
  # Iterate over all websites and generate a module block for each
  - for_each: input.websites
    target: "module.cloudfront_s3_website_${item.name}"
    value:
      # The standard source property Terraform expects
      source: "terraform-aws-modules/s3-bucket/aws//modules/notification" # Example registry path
      version: "4.1.0"

      # Passing dynamic values directly into the module variables
      bucket_name: "mycompany-web-${item.name}"
      domain_name: ${item.domain}
      price_class: ${item.price_class}

      tags:
        ManagedBy: "Watt TF"
        Owner: ${input.team}

3. Execution

When you run wtf build, Watt TF automatically expands the blueprint into the exact structural JSON format that Terraform needs to resolve and download the modules:

# 1. Generate the modules JSON
wtf build -i input.yaml -b blueprint.yaml -o static-sites.tf.json

# 2. Let Terraform fetch and apply the remote modules
terraform init
terraform apply -auto-approve

The generated static-sites.tf.json will look like this:

{
  "module": {
    "cloudfront_s3_website_corporate_blog": {
      "source": "terraform-aws-modules/s3-bucket/aws//modules/notification",
      "version": "4.1.0",
      "bucket_name": "mycompany-web-corporate-blog",
      "domain_name": "blog.mycompany.com",
      "price_class": "PriceClass_100",
      "tags": {
        "ManagedBy": "Watt TF",
        "Owner": "marketing"
      }
    },
    "cloudfront_s3_website_documentation": {
      "source": "terraform-aws-modules/s3-bucket/aws//modules/notification",
      "version": "4.1.0",
      "bucket_name": "mycompany-web-documentation",
      "domain_name": "docs.mycompany.com",
      "price_class": "PriceClass_All",
      "tags": {
        "ManagedBy": "Watt TF",
        "Owner": "marketing"
      }
    }
  }
}