Terragrunt for Beginners
Terragrunt Functions
read terragrunt config
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:
read_terragrunt_config("<path/to/file.hcl>")
Terragrunt will:
- Parse the specified HCL file.
- Serialize its contents into a map.
- 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. |
Tip
Use clear naming conventions in your common.hcl to avoid confusion when referencing nested attributes.
Example: Sharing Common Variables
Create a root-level common.hcl with project-wide variables:
# common.hcl
inputs = {
project = "KodeKloud"
environment = "dev"
}
In the vpc/ directory, import these inputs using read_terragrunt_config:
# 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:
- Terragrunt reads
../common.hcl. local.common_vars.inputscontains:project:"KodeKloud"environment:"dev"
- The VPC module’s
nameinput resolves to:
KodeKloud-dev-VPC
Warning
Verify the relative path to common.hcl, or Terragrunt will error out with a file-not-found.
Initializing Terragrunt
Run the following in the vpc/ directory:
$ terragrunt init
Expected output:
- 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!
Next Steps
After initialization, run terragrunt plan to preview changes based on your dynamic inputs.
Links and References
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