Terragrunt Note

Terragrunt wraps Terraform to keep configurations DRY across environments. The config file is named terragrunt.hcl.

Core blocks

Block	Purpose
terraform	Points to the Terraform source module and adds extra CLI arguments or hooks.
include	Inherits a parent terragrunt.hcl so environment configs reuse shared settings.
locals	Defines aliases and computed values inside the current file.
remote_state	Configures the backend (S3, GCS, Azure, etc.) once for all child configs.
generate	Creates additional Terraform files, such as a backend configuration, at runtime.

Example: backend generation

# terragrunt.hcl
remote_state {
  backend = "s3"

  config = {
    bucket         = "terraform-statefiles-aws-vpc"
    key            = "${path_relative_to_include()}/terraform.tfstate"
    region         = "us-west-2"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }

  generate = {
    path      = "s3-backend.tf"
    if_exists = "overwrite_terragrunt"
  }
}

This generates s3-backend.tf in each child directory with the S3 backend configuration.

Example: include a parent config

# dev/terragrunt.hcl
include "root" {
  path = find_in_parent_folders("root.hcl")
}

find_in_parent_folders() walks up the directory tree until it finds root.hcl. Each child can include only one block with the same label, but different labels are allowed if you need more than one inclusion.

Example: terraform source and hooks

# terragrunt.hcl
terraform {
  source = "git::https://github.com/org/terraform-modules.git//vpc?ref=v1.2.0"

  extra_arguments "common_vars" {
    commands = [
      "apply",
      "plan",
    ]

    arguments = [
      "-var-file=../common.tfvars",
    ]
  }

  before_hook "before_hook" {
    commands = ["apply"]
    execute  = ["echo", "Running apply"]
  }
}

Completion criterion

After reading this, you should be able to:

1. Name the config file and place it correctly in a Terragrunt project.
2. Use include to inherit a parent configuration.
3. Use remote_state with generate to create a backend file automatically.
4. Add extra arguments and hooks to Terraform commands.

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