Terraform Advanced — Terragrunt Exercises

Practice Terragrunt patterns.

---

Exercise 1 — Root Config

Task: Write a root terragrunt.hcl that auto-generates S3 backend config with dynamic keys and an AWS provider for us-west-2.

Answer

remote_state {
  backend = "s3"
  generate = {
    path      = "backend.tf"
    if_exists = "overwrite_terragrunt"
  }
  config = {
    bucket         = "mycompany-tf-state"
    key            = "${path_relative_to_include()}/terraform.tfstate"
    region         = "us-west-2"
    dynamodb_table = "tf-locks"
    encrypt        = true
  }
}

generate "provider" {
  path      = "provider.tf"
  if_exists = "overwrite_terragrunt"
  contents  = <<EOF
provider "aws" {
  region = "us-west-2"
}
EOF
}

---

Exercise 2 — Child with Dependency

Task: Write a child terragrunt.hcl for an EKS stack that depends on a VPC stack and passes vpc_id and subnet_ids.

Answer

include "root" {
  path = find_in_parent_folders()
}

terraform {
  source = "../../../modules/eks"
}

dependency "vpc" {
  config_path = "../vpc"
  mock_outputs = {
    vpc_id     = "vpc-mock"
    subnet_ids = ["subnet-mock"]
  }
}

inputs = {
  cluster_name = "prod-eks"
  vpc_id       = dependency.vpc.outputs.vpc_id
  subnet_ids   = dependency.vpc.outputs.subnet_ids
}

---

Exercise 3 — Selective Apply

Task: Write the command to apply only VPC and EKS stacks in the prod environment, with parallelism of 1.

Answer

$ cd environments/prod
$ terragrunt run-all apply \
    --terragrunt-include-dir "*/vpc" \
    --terragrunt-include-dir "*/eks" \
    --terragrunt-parallelism 1

---

Chapter Summary

• Terragrunt eliminates code duplication across environments
• path_relative_to_include() auto-generates unique state keys
• dependency blocks reference outputs from other stacks
• Mock outputs enable plan before dependencies are applied
• run-all applies entire environments in dependency order

---

← run-all Commands Chapter 6: Importing Infrastructure →