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Leverage the Terraform Registry to discover, share, and reuse community-maintained modules. When you integrate Terragrunt, you can reference these modules directly using the tfr:// protocol.

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1. Referencing a Module in Terragrunt

In your terragrunt.hcl file, set the source attribute to point at a Registry module: 
# terragrunt.hcl
terraform {
  source = "tfr://<namespace>/<module_name>/<provider>"
}
ElementDescriptionExample
namespaceAuthor or organization publishing the moduleterraform-aws-modules
module_nameIdentifier for the modulevpc
providerCloud provider nameaws
Example: 
terraform {
  source = "tfr://terraform-aws-modules/vpc/aws"
}

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2. Initializing the Configuration

Run the following command to download and prepare the module in your working directory: 
terragrunt init
This initializes your Terragrunt configuration and fetches the specified module from the Terraform Registry.

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3. Pinning a Module Version

To guarantee reproducible builds and avoid unintended upgrades, specify a version constraint: 
terraform {
  source  = "tfr://terraform-aws-modules/vpc/aws"
  version = "~> 3.0"
}
Modules in the Registry follow semantic versioning. Locking to ~> 3.0 ensures you get all non-breaking updates in the 3.x series.

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4. Updating to the Latest Matching Version

When you’re ready to pull in the newest matching release (within your version constraint), use: 
terragrunt get --update
This command refreshes your local copy of the module, incorporating any fixes or enhancements.

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5. Security and Best Practices

Always verify the module’s publisher and review its source code before applying in production. Prefer modules marked as Verified or provided by official vendors to reduce risk.
  • Review module inputs, outputs, and provisioners for security compliance.
  • Check the Terraform Registry page for the module’s documentation and changelog.
  • Use version pinning to control when features and fixes are introduced.

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