> ## 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.

# read terragrunt config

> This lesson explores Terragrunts `read_terragrunt_config` function for reading HCL files and returning their contents as a map.

In this lesson, we’ll dive into Terragrunt’s built-in function `read_terragrunt_config`, which reads a Terragrunt HCL file and returns its contents as a map. This enables you to:

* Dynamically consume inputs, outputs, blocks, and attributes from another configuration.
* Adapt resources for different environments or setups.
* Promote modularity, reusability, and DRY infrastructure code.

When you invoke:

```hcl theme={null}
read_terragrunt_config("<path/to/file.hcl>")
```

Terragrunt will:

1. Parse the specified HCL file.
2. Serialize its contents into a map.
3. Expose all blocks and attributes under that map for referencing in your configuration.

## Key Benefits

* **Dynamic Configuration**: Tailor resources per environment.
* **Modularity**: Reuse shared inputs and outputs.
* **Maintainability**: Avoid duplication across modules.

## Best Practices

| Practice                 | Recommendation                                           |
| ------------------------ | -------------------------------------------------------- |
| Centralize common inputs | Store project-level variables in a root `common.hcl`.    |
| Use `locals` for mapping | Assign descriptive local names to imported values.       |
| Keep shared configs lean | Include only widely used variables to reduce complexity. |
| Verify relative paths    | Ensure the path passed to the function is correct.       |

<Frame>
  ![The image outlines best practices for "read\_terragrunt\_config," highlighting the need for resources to adapt dynamically and access input/output configurations.](https://kodekloud.com/kk-media/image/upload/v1752884356/notes-assets/images/Terragrunt-for-Beginners-read-terragrunt-config/best-practices-read-terragrunt-config.jpg)
</Frame>

<Callout icon="lightbulb" color="#1CB2FE">
  Use clear naming conventions in your `common.hcl` to avoid confusion when referencing nested attributes.
</Callout>

***

## Example: Sharing Common Variables

Create a root-level `common.hcl` with project-wide variables:

```hcl theme={null}
# common.hcl
inputs = {
  project     = "KodeKloud"
  environment = "dev"
}
```

In the `vpc/` directory, import these inputs using `read_terragrunt_config`:

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

locals {
  common_vars = read_terragrunt_config("../common.hcl")
}

inputs = {
  name = "${local.common_vars.inputs.project}-${local.common_vars.inputs.environment}-VPC"
}
```

What happens under the hood:

1. Terragrunt reads `../common.hcl`.
2. `local.common_vars.inputs` contains:
   * `project`: `"KodeKloud"`
   * `environment`: `"dev"`
3. The VPC module’s `name` input resolves to:

```text theme={null}
KodeKloud-dev-VPC
```

<Callout icon="triangle-alert" color="#FF6B6B">
  Verify the relative path to `common.hcl`, or Terragrunt will error out with a file-not-found.
</Callout>

***

## Initializing Terragrunt

Run the following in the `vpc/` directory:

```bash theme={null}
$ terragrunt init
```

Expected output:

```text theme={null}
- Finding hashicorp/aws versions matching ">= 5.30.0"...
- Installing hashicorp/aws v5.52.0...
- Installed hashicorp/aws v5.52.0 (signed by HashiCorp)

Terraform has created a lock file .terraform.lock.hcl ...
Terraform has been successfully initialized!
```

<Callout icon="lightbulb" color="#1CB2FE">
  After initialization, run `terragrunt plan` to preview changes based on your dynamic inputs.
</Callout>

***

## Links and References

* [Terragrunt Function Reference](https://github.com/gruntwork-io/terragrunt#functions)
* [Terraform AWS VPC Module](https://github.com/terraform-aws-modules/terraform-aws-vpc)
* [Terragrunt Official Documentation](https://terragrunt.gruntwork.io/docs/)

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