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In this guide, we’ll demonstrate how to source the same S3 bucket module from the Terraform Registry using Terragrunt. Instead of pulling the module from GitHub, we switch to the tfr:/// prefix and pin a specific version. This approach simplifies version management and leverages the official Terraform Registry distribution.

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Why Use the Terraform Registry?

Source TypePrefixExample Address
GitHubgit::https://github.com/...git::https://github.com/terraform-aws-modules/terraform-aws-s3-bucket.git
Terraform Registrytfr:///tfr:///terraform-aws-modules/s3-bucket/aws?version=4.1.2
Pinning module versions (e.g. ?version=4.1.2) ensures reproducible builds and prevents unexpected changes when upstream modules are updated.

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terragrunt.hcl Configuration

Create or update your terragrunt.hcl file with the registry source and input variables: 
# terragrunt.hcl
terraform {
  source = "tfr:///terraform-aws-modules/s3-bucket/aws?version=4.1.2"
}

inputs = {
  bucket = "my-unique-bucket-name"
  acl    = "private"

  public_access_block = {
    block_public_acls       = true
    block_public_policy     = true
    ignore_public_acls      = true
    restrict_public_buckets = true
  }
}
The syntax breakdown:
  • tfr:/// — Registry prefix (two slashes for delimiter + one slash to start address).
  • namespace/module_name/provider — Module path on the Terraform Registry.
  • ?version=x.y.z — Query parameter to lock the module version.

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Initialize and Apply with Terragrunt

Run the following commands to download the module and provision your S3 bucket: 
$ terragrunt init
[terragrunt]  INFO: Downloading module...
...

$ terragrunt apply --auto-approve
...
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

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Verify the S3 Bucket

Use the AWS CLI to confirm that your bucket exists: 
$ aws s3 ls
2023-08-15 12:34:56 my-unique-bucket-name
Bucket names must be globally unique. If you encounter an error about the bucket already existing, choose a different name.

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