ABOUTME: Terraform/Terragrunt IaC patterns, modules, state management

ABOUTME: Best practices for HCL, DRY configs, security scanning

Terraform & Terragrunt

OpenTofu: open-source (MPL) fork, recommended for new projects because Terraform is BSL-licensed. The two have diverged since the fork, so check feature parity against the version the project runs.

Quick Reference

terraform init|plan|apply|destroy
terragrunt run --all apply
terraform fmt -recursive && terraform validate
terraform state list|show|rm|mv <resource>

See: _AST_GREP.md (sg patterns for HCL)

Project Structure

Simple: main.tf, variables.tf, outputs.tf, versions.tf

Multi-env:

terraform/
├── modules/{vpc,eks}/
└── environments/{dev,staging,prod}/

TF 1.5+ Blocks

import { to = aws_instance.web; id = "i-1234567890abcdef0" }
moved { from = aws_instance.web; to = module.web.aws_instance.main }
check "health" {
  data "http" "api" { url = "https://api.example.com/health" }
  assert { condition = data.http.api.status_code == 200; error_message = "API down" }
}

Terragrunt

Benefits: DRY configs, multi-env mgmt, dependency ordering, auto backend config

Structure

infrastructure/
├── terragrunt.hcl           # Root
├── _envcommon/{vpc,eks}.hcl
├── {dev,staging,prod}/
│   └── {region}/{vpc,eks}/terragrunt.hcl

Dependencies

dependency "vpc" { config_path = "../vpc" }
inputs = { vpc_id = dependency.vpc.outputs.vpc_id }

State Management

Split by: env, region, component, blast radius

backend "s3" { bucket = "my-state"; key = "prod/terraform.tfstate"; encrypt = true; use_lockfile = true }  # S3-native locking; dynamodb_table only on versions without it

Testing & Security

Pipeline: fmt/validate → TFLint → Checkov/Trivy → Infracost

terraform fmt -check -recursive && terraform validate
tflint --recursive
checkov -d . --framework terraform --compact
infracost breakdown --path .

Code Review Checklist

Security: No hardcoded secrets, encrypted state, locking enabled, least-privilege IAM, Checkov passes

Structure: Versioned modules, validated variables, consistent naming

Resources

Docs: Terraform, OpenTofu, Terragrunt