Terragrunt Generator

Overview

Generate production-ready Terragrunt configurations following current best practices, naming conventions, and security standards. All generated configurations are automatically validated.

Trigger Phrases

Use this skill when the user asks for:

• A new root.hcl, terragrunt.hcl, or terragrunt.stack.hcl
• Multi-environment Terragrunt layouts (dev/staging/prod)
• Terragrunt dependency wiring (dependency or dependencies blocks)
• Terragrunt module source setup (local, Git, Terraform Registry via tfr:///)
• Stack catalog unit generation under catalog/units/*

Terragrunt 2025 Features Supported:

• Stacks - Infrastructure blueprints with terragrunt.stack.hcl (GA since v0.78.0)
• Feature Flags - Runtime control via feature blocks
• Exclude Blocks - Fine-grained execution control (replaces deprecated skip)
• Errors Blocks - Advanced error handling (replaces deprecated retryable_errors)
• OpenTofu Engine - Alternative IaC engine support

Root Configuration Naming

RECOMMENDED: Use root.hcl instead of terragrunt.hcl for root files per migration guide.

Include standard: Default to find_in_parent_folders("root.hcl") in all new examples and generated configs. Use find_in_parent_folders() only when explicitly targeting a legacy root file named terragrunt.hcl.

Architecture Patterns

CRITICAL: Before generating ANY configuration, you MUST determine the architecture pattern and understand its constraints.

Pattern A: Multi-Environment with Environment-Agnostic Root

Use when: Managing multiple environments (dev/staging/prod) with shared root configuration.

Key principle: root.hcl is environment-agnostic - it does NOT read environment-specific files.

infrastructure/
├── root.hcl              # Environment-AGNOSTIC (no env.hcl references)
├── dev/
│   ├── env.hcl           # Environment variables (locals block)
│   ├── vpc/terragrunt.hcl
│   └── rds/terragrunt.hcl
└── prod/
    ├── env.hcl           # Environment variables (locals block)
    ├── vpc/terragrunt.hcl
    └── rds/terragrunt.hcl

Root.hcl constraints:

• ❌ CANNOT use read_terragrunt_config(find_in_parent_folders("env.hcl")) - env.hcl doesn't exist at root level
• ❌ CANNOT reference local.environment or local.aws_region that come from env.hcl
• ✅ CAN use static values or get_env() for runtime configuration
• ✅ CAN use ${path_relative_to_include()} for state keys (this works dynamically)

Child modules read env.hcl:

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

locals {
  env = read_terragrunt_config(find_in_parent_folders("env.hcl"))
}

inputs = {
  name = "${local.env.locals.environment}-vpc"  # Works: env.hcl exists in dev/
}

Pattern B: Single Environment or Environment-Aware Root

Use when: Single environment OR all environments share the same root with environment detection.

infrastructure/
├── root.hcl              # Can be environment-aware via get_env() or directory parsing
├── account.hcl           # Account-level config (optional)
├── region.hcl            # Region-level config (optional)
└── vpc/
    └── terragrunt.hcl

Root.hcl can detect environment:

# root.hcl - environment detection via directory path
locals {
  # Parse environment from path (e.g., "prod/vpc" -> "prod")
  path_parts  = split("/", path_relative_to_include())
  environment = local.path_parts[0]

  # OR use environment variable
  environment = get_env("TG_ENVIRONMENT", "dev")
}

Pattern C: Shared Environment Variables (_env directory)

Use when: Centralizing environment variables with symlinks or direct references.

infrastructure/
├── root.hcl              # Environment-AGNOSTIC
├── _env/                 # Centralized environment definitions
│   ├── prod.hcl
│   ├── staging.hcl
│   └── dev.hcl
├── prod/
│   ├── env.hcl           # Reads from _env/prod.hcl
│   └── vpc/terragrunt.hcl
└── dev/
    ├── env.hcl           # Reads from _env/dev.hcl
    └── vpc/terragrunt.hcl

env.hcl reads from _env:

# prod/env.hcl
locals {
  env_vars = read_terragrunt_config("${get_repo_root()}/_env/prod.hcl")

  # Re-export for child modules
  environment        = local.env_vars.locals.environment
  aws_region         = local.env_vars.locals.aws_region
  vpc_cidr           = local.env_vars.locals.vpc_cidr
  # ... other variables
}

Architecture Pattern Selection Checklist (Canonical)

MANDATORY: Before writing any files, you MUST complete this checklist and OUTPUT it to the user with checkmarks filled in. This is not optional.

Output this completed checklist before generating any files:

## Architecture Pattern Selection

[x] Identified architecture pattern: Pattern ___ (A/B/C)
[x] Root.hcl scope: [ ] environment-agnostic  OR  [ ] environment-aware
[x] env.hcl location: ___________________
[x] Child modules access env via: ___________________
[x] Verified: No file references a path that doesn't exist from its location

Example completed checklist:

## Architecture Pattern Selection

[x] Identified architecture pattern: Pattern A (Multi-Environment with Environment-Agnostic Root)
[x] Root.hcl scope: [x] environment-agnostic  OR  [ ] environment-aware
[x] env.hcl location: dev/env.hcl, prod/env.hcl (one per environment)
[x] Child modules access env via: read_terragrunt_config(find_in_parent_folders("env.hcl"))
[x] Verified: No file references a path that doesn't exist from its location

Quick Variable Definition Examples

Use these starter files for Pattern B and account/region-aware setups.

env.hcl

locals {
  environment = "dev"
  aws_region  = "us-east-1"
  project     = "platform"
}

account.hcl

locals {
  account_id   = "123456789012"
  account_name = "shared-services"
}

region.hcl

locals {
  aws_region = "us-east-1"
}

When to Use

• Creating new Terragrunt projects or configurations
• Setting up multi-environment infrastructure (dev/staging/prod)
• Implementing DRY Terraform configurations
• Managing complex infrastructure with dependencies
• Working with custom Terraform providers or modules

Core Capabilities

1. Generate Root Configuration

Create root-level root.hcl or terragrunt.hcl with remote state, provider config, and common variables.

MANDATORY: Before generating, READ the template file:

Read: assets/templates/root/terragrunt.hcl

Template: assets/templates/root/terragrunt.hcl Patterns: references/common-patterns.md → Root Configuration Patterns

Key placeholders to replace:

• [BUCKET_NAME], [AWS_REGION], [DYNAMODB_TABLE]
• [TERRAFORM_VERSION], [PROVIDER_NAME], [PROVIDER_SOURCE], [PROVIDER_VERSION]
• [ENVIRONMENT], [PROJECT_NAME]

Root.hcl Design Principles:

1. Environment-agnostic by default - Don't assume env.hcl exists at root level
2. Use static values for provider/backend region - Or use get_env() for runtime config
3. State key uses path_relative_to_include() - This automatically includes environment path
4. Provider tags can be static - Environment-specific tags go in child modules

2. Generate Child Module Configuration

Create child modules with dependencies, mock outputs, and proper includes.

MANDATORY: Before generating, READ the template file:

Read: assets/templates/child/terragrunt.hcl

Template: assets/templates/child/terragrunt.hcl Patterns: references/common-patterns.md → Child Module Patterns

Module source options:

• Local: "../../modules/vpc"
• Git: "git::https://github.com/org/repo.git//path?ref=v1.0.0"
• Registry: "tfr:///terraform-aws-modules/vpc/aws?version=5.1.0"

3. Generate Standalone Module

Self-contained modules without root dependency.

MANDATORY: Before generating, READ the template file:

Read: assets/templates/module/terragrunt.hcl

Template: assets/templates/module/terragrunt.hcl

Canonical Placeholder Replacement Map

Use this map for every generated output:

Legacy alias normalization: If you see [REGION] in older examples, treat it as [AWS_REGION] and replace it before validation.

4. Generate Multi-Environment Infrastructure

Complete directory structures for dev/staging/prod.

MANDATORY: Before generating:

1. Determine architecture pattern (see Architecture Patterns section)
2. Read relevant templates for root, env, and child modules
3. Verify env.hcl placement and access patterns:

   Read: assets/templates/env/env.hcl
   

Patterns: references/common-patterns.md → Environment-Specific Patterns

Typical structure (Pattern A - Environment-Agnostic Root):

infrastructure/
├── root.hcl              # Environment-AGNOSTIC root config
├── dev/
│   ├── env.hcl           # Dev environment variables
│   └── vpc/terragrunt.hcl
└── prod/
    ├── env.hcl           # Prod environment variables
    └── vpc/terragrunt.hcl

5. Generate Terragrunt Stacks (2025)

Infrastructure blueprints using terragrunt.stack.hcl.

MANDATORY: Before generating, READ the template files:

Read: assets/templates/stack/terragrunt.stack.hcl
Read: assets/templates/catalog/terragrunt.hcl

Docs: Stacks Documentation Template: assets/templates/stack/terragrunt.stack.hcl Catalog Template: assets/templates/catalog/terragrunt.hcl Patterns: references/common-patterns.md → Stacks Patterns

Stack path rule: Keep no_dot_terragrunt_stack mode consistent across dependent units. Do not mix direct-path and .terragrunt-stack generation in the same dependency chain.

Commands:

terragrunt stack generate    # Generate unit configurations
terragrunt stack run plan    # Plan all units
terragrunt stack run apply   # Apply all units
terragrunt stack output      # Get aggregated outputs
terragrunt stack clean       # Clean generated directories

6. Generate Feature Flags (2025)

Runtime control without code changes.

Docs: Feature Flags Documentation Patterns: references/common-patterns.md → Feature Flags Patterns

CRITICAL: Feature flag default values MUST be static (boolean, string, number). They CANNOT reference local.* values. Use static defaults and override via CLI/env vars.

Correct:

feature "enable_monitoring" {
  default = false  # Static value - OK
}

Incorrect:

feature "enable_monitoring" {
  default = local.env.locals.enable_monitoring  # Dynamic reference - FAILS
}

Usage:

terragrunt apply --feature enable_monitoring=true
# or

Environment-specific defaults: Use different static defaults per environment file, not dynamic references.

7. Generate Exclude Blocks (2025)

Fine-grained execution control (replaces deprecated skip).

Docs: Exclude Block Reference Patterns: references/common-patterns.md → Exclude Block Patterns

Actions: "plan", "apply", "destroy", "all", "all_except_output"

Production Recommendation: For critical production resources, add exclude blocks to prevent accidental destruction:

# Protect production databases from accidental destroy
exclude {
  if      = true
  actions = ["destroy"]
  exclude_dependencies = false
}

# Also use prevent_destroy for critical resources
prevent_destroy = true

8. Generate Errors Blocks (2025)

Advanced error handling (replaces deprecated retryable_errors).

Docs: Errors Block Reference Patterns: references/common-patterns.md → Errors Block Patterns

9. Generate OpenTofu Engine Configuration (2025)

Use OpenTofu as the IaC engine.

Docs: Engine Documentation Patterns: references/common-patterns.md → OpenTofu Engine Patterns

10. Handling Custom Providers/Modules

When generating configs with custom providers:

1. Identify the provider name, source, and version
2. Search using WebSearch: "[provider] terraform provider [version] documentation"
3. Or use Context7 MCP if available for structured docs
4. Generate with proper required_providers block
5. Document authentication requirements in comments

Generation Workflow

CRITICAL: Follow this workflow for EVERY generation task. Skipping steps leads to validation errors.

Step 1: Understand Requirements

• What type of configuration? (root, child, standalone, stack)
• Single or multi-environment?
• What dependencies exist between modules?
• What providers/modules will be used?

Step 2: Determine Architecture Pattern

MANDATORY: Select and document the pattern BEFORE writing any files.