> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# terraform Block

> The article explains the Terraform block in Terragrunt, detailing its attributes and how to configure it for consistent Terraform behavior.

The Terraform block in Terragrunt defines how Terragrunt locates and invokes your Terraform configuration. It centralizes settings such as module source, version locking, extra CLI arguments, and lifecycle hooks. By configuring this block once, you ensure consistent Terraform behavior across all environments and modules.

## Key Terraform Block Attributes

| Attribute         | Description                                                                          | Example                                                                      |
| ----------------- | ------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------- |
| `source`          | Location of the Terraform module (Registry, Git repo, or local path)                 | `source = "tfr://terraform-aws-modules/vpc/aws/?version=5.8.1"`              |
| `version` / `ref` | Locks a Registry module or Git source to a specific version or commit                | `?version=5.8.1` (Registry) / `?ref=v1.2.0` (Git)                            |
| `extra_arguments` | Defines additional CLI flags or variable files to pass to Terraform                  | `arguments = ["-var-file=prod.tfvars"]`                                      |
| `hooks`           | `before_hook` or `after_hook` blocks for executing scripts around Terraform commands | `before_hook "lint" { commands = ["plan"]; execute = ["npm","run","lint"] }` |

<Callout icon="lightbulb" color="#1CB2FE">
  Always lock your modules to a specific `version` or `ref` to avoid unintended upgrades.\
  For Registry modules, append `?version=`, and for Git sources, use `?ref=`.
</Callout>

***

## 1. Defining the Source

The `source` attribute tells Terragrunt where to fetch Terraform code. You can reference:

* **Terraform Registry Modules**
* **Git Repositories** (HTTPS or SSH)
* **Local Directories**

### 1.1 Terraform Registry

```hcl theme={null}
terraform {
  source = "tfr://terraform-aws-modules/vpc/aws/?version=5.8.1"
}
```

Include subdirectories by adding extra slashes:

```hcl theme={null}
terraform {
  source = "tfr://terraform-aws-modules/vpc/aws//modules/subnet?version=5.8.1"
}
```

### 1.2 GitHub (HTTPS)

```hcl theme={null}
terraform {
  source = "github.com/terraform-aws-modules/terraform-aws-vpc?ref=v5.8.1"
}
```

### 1.3 GitHub (SSH)

```hcl theme={null}
terraform {
  source = "git@github.com:terraform-aws-modules/terraform-aws-vpc.git?ref=v5.8.1"
}
```

### 1.4 Local Modules

Ideal for local development and testing:

```hcl theme={null}
terraform {
  source = "../modules/vpc-module"
}
```

***

## 2. Passing Extra Arguments

Use `extra_arguments` to pass flags, variable files, or arbitrary flags to Terraform:

```hcl theme={null}
terraform {
  extra_arguments "prod_vars" {
    commands  = get_terraform_commands_that_need_vars()
    arguments = ["-var-file=prod.tfvars"]
  }
}
```

| Field       | Description                                        |
| ----------- | -------------------------------------------------- |
| `commands`  | List of Terraform commands (e.g., `plan`, `apply`) |
| `arguments` | Array of CLI flags or variable file references     |

***

## 3. Hooks and Custom Commands

Hooks allow you to run scripts before or after Terraform commands:

```hcl theme={null}
terraform {
  before_hook "validate_schema" {
    commands = ["plan", "apply"]
    execute  = ["python", "scripts/validate.py"]
  }

  after_hook "notify" {
    commands = ["apply"]
    execute  = ["bash", "scripts/notify.sh"]
  }
}
```

| Hook Type     | Purpose                                         |
| ------------- | ----------------------------------------------- |
| `before_hook` | Run tasks prior to Terraform execution          |
| `after_hook`  | Run cleanup or notifications post Terraform run |

<Callout icon="triangle-alert" color="#FF6B6B">
  Use hooks carefully in production: unexpected script failures can block Terraform runs.\
  Always test hooks in a development environment first.
</Callout>

***

## References

* [Terragrunt Documentation](https://terragrunt.gruntwork.io/docs/)
* [Terraform Registry](https://registry.terraform.io/)
* [GitHub Modules](https://github.com/terraform-aws-modules)

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