Terragrunt Generator

Overview

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

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.

Approach	Root File	Include Syntax
Modern	`root.hcl`	`find_in_parent_folders("root.hcl")`
Legacy	`terragrunt.hcl`	`find_in_parent_folders()`

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
}

Pre-Generation Pattern Checklist

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

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_VERSION]
[ENVIRONMENT], [PROJECT_NAME]

Root.hcl Design Principles:

Environment-agnostic by default - Don't assume env.hcl exists at root level
Use static values for provider/backend region - Or use get_env() for runtime config
State key uses path_relative_to_include() - This automatically includes environment path
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

4. Generate Multi-Environment Infrastructure

Complete directory structures for dev/staging/prod.

MANDATORY: Before generating:

Determine architecture pattern (see Architecture Patterns section)

Read relevant templates for root and child modules

Verify env.hcl placement and access patterns

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

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
export TG_FEATURE="enable_monitoring=true"

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:

Identify the provider name, source, and version
Search using WebSearch: "[provider] terraform provider [version] documentation"
Or use Context7 MCP if available for structured docs
Generate with proper required_providers block
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.

Scenario	Pattern	Root.hcl Scope
Multi-env with shared root	Pattern A	Environment-agnostic
Single environment	Pattern B	Environment-aware
Centralized env vars	Pattern C	Environment-agnostic

Verify:

[ ] Pattern identified: ____
[ ] Root.hcl will be: [ ] environment-agnostic  [ ] environment-aware
[ ] env.hcl will be located in: ____
[ ] Child modules will read env.hcl via: ____

Step 3: Read Required Templates

MANDATORY: Read the relevant template file(s) BEFORE generating each configuration type.

Configuration Type	Template to Read
Root configuration	`assets/templates/root/terragrunt.hcl`
Child module	`assets/templates/child/terragrunt.hcl`
Standalone module	`assets/templates/module/terragrunt.hcl`
Stack file	`assets/templates/stack/terragrunt.stack.hcl`
Catalog unit	`assets/templates/catalog/terragrunt.hcl`

Also read:

references/common-patterns.md - Primary source for generation patterns

Step 4: Generate with Validation

Validation Strategy: Use a combination of inline checks during generation and batch validation at the end.

Generation order for multi-environment projects:

Generate root.hcl first
- Inline checks (during generation):
  - No read_terragrunt_config(find_in_parent_folders("env.hcl")) if environment-agnostic
  - remote_state block has encrypt = true
  - errors block used (not deprecated retryable_errors)
Generate env.hcl files for each environment
- Inline checks (during generation):
  - locals block contains environment, aws_region, and module-specific vars
  - No references to files that don't exist at that directory level
Generate child modules (VPC, etc.) - modules with NO dependencies first
- Inline checks (during generation):
  - include block uses find_in_parent_folders("root.hcl")
  - read_terragrunt_config(find_in_parent_folders("env.hcl")) present
  - terraform.source uses valid syntax (tfr:///, git::, or relative path)
Generate dependent modules (RDS, EKS, etc.)
- Inline checks (during generation):
  - dependency blocks have mock_outputs
  - mock_outputs_allowed_terraform_commands includes ["validate", "plan", "destroy"]
  - Production modules have prevent_destroy = true and/or exclude block
Run batch validation after ALL files are generated

Note: Full CLI validation (terragrunt hcl fmt, terragrunt dag graph) requires all files to exist, so these are batched at the end.
```
# Batch validation commands (run after all files exist):
terragrunt hcl fmt --check          # Format validation
terragrunt dag graph                 # Dependency graph validation
```
- Invoke devops-skills:terragrunt-validator skill for comprehensive validation

Step 5: Fix and Re-Validate

If validation fails:

Analyze errors (path resolution, missing variables, syntax errors)
Fix issues in the specific file(s)
Re-validate the fixed file(s)
Repeat until ALL errors are resolved

Step 6: Present Results

Follow "Presentation Requirements" section below.

Validation Workflow

CRITICAL: Every generated configuration MUST be validated.

Incremental Validation Checks

After generating root.hcl:

cd <infrastructure-directory>
terragrunt hcl fmt --check

After generating each child module:

cd <module-directory>
terragrunt hcl fmt --check
# If no dependencies on other modules:
terragrunt hcl validate --inputs

Full Validation

After all files are generated:

Invoke validation skill:

Invoke: devops-skills:terragrunt-validator skill

If validation fails:
- Analyze errors (missing placeholders, invalid syntax, wrong paths)
- Fix issues
- Re-validate (repeat until ALL errors are resolved)
If validation succeeds: Present configurations with usage instructions

Skip validation only for: Partial snippets, documentation examples, or explicit user request

Presentation Requirements

MANDATORY: After successful validation, you MUST present ALL of the following sections. Incomplete presentation is not acceptable. Copy and fill in the templates below.

1. Directory Structure Summary (MANDATORY)

# Show the generated structure
tree <infrastructure-directory>

2. Files Generated (MANDATORY)

Output this table with all generated files:

| File | Purpose |
|------|---------|
| root.hcl | Shared configuration for all child modules (state backend, provider) |
| dev/env.hcl | Development environment variables |
| prod/env.hcl | Production environment variables |
| dev/vpc/terragrunt.hcl | VPC module for development |
| ... | ... |

3. Usage Instructions (MANDATORY)

You MUST include this section. Copy the template below and fill in the actual values:

## Usage Instructions

### Prerequisites
Before running Terragrunt commands, ensure:
1. AWS credentials are configured (`aws configure` or environment variables)
2. S3 bucket `<BUCKET_NAME>` exists for state storage
3. DynamoDB table `<TABLE_NAME>` exists for state locking

### Commands

# Navigate to infrastructure directory
cd <INFRASTRUCTURE_DIR>

# Initialize all modules
terragrunt run --all init

# Preview changes for a specific environment
cd <ENV>/vpc && terragrunt plan

# Preview all changes
terragrunt run --all plan

# Apply changes (requires approval)
terragrunt run --all apply

# Destroy (use with extreme caution)
terragrunt run --all destroy

4. Environment-Specific Notes (MANDATORY)

You MUST include this section. Copy the template below and fill in the actual values:

## Environment Notes

### Required Environment Variables
| Variable | Description | Example |
|----------|-------------|---------|
| AWS_PROFILE | AWS CLI profile to use | `my-profile` |
| AWS_REGION | AWS region (or set in provider) | `us-east-1` |

### Prerequisites
- [ ] S3 bucket `<BUCKET_NAME>` must exist before first run
- [ ] DynamoDB table `<TABLE_NAME>` must exist for state locking
- [ ] IAM permissions for Terraform state management

### Production-Specific Protections
| Module | Protection | Description |
|--------|------------|-------------|
| prod/rds | `prevent_destroy = true` | Prevents accidental database deletion |
| prod/rds | `exclude { actions = ["destroy"] }` | Blocks destroy commands |

5. Next Steps (Optional)

Suggest what the user might want to do next (add more modules, customize configurations, etc.)

Best Practices

Reference ../devops-skills:terragrunt-validator/references/best_practices.md for comprehensive guidelines.

Key principles:

Use include blocks to inherit root configuration (DRY)
Always provide mock outputs for dependencies
Enable state encryption (encrypt = true)
Use generate blocks for provider configuration
Specify bounded version constraints (~> 5.0, not >= 5.0) for local/Git modules
Never hardcode credentials or secrets
Configure retry logic for transient errors

Note on Version Constraints with Registry Modules: When using Terraform Registry modules (e.g., tfr:///terraform-aws-modules/vpc/aws?version=5.1.0), they typically define their own required_providers. In this case, you may omit generating required_providers in root.hcl to avoid conflicts. The module's pinned version (?version=X.X.X) provides the version constraint. See "Common Issues → Provider Conflict with Registry Modules" for details.

Anti-patterns to avoid:

Hardcoded account IDs, regions, or environment names
Missing mock outputs for dependencies
Duplicated configuration across modules
Unencrypted state storage
Missing or loose version constraints (except when using registry modules that define their own)
Root.hcl trying to read env.hcl that doesn't exist at root level

Deprecated Attributes

Deprecated	Replacement	Reference
`skip`	`exclude` block	Docs
`retryable_errors`	`errors.retry` block	Docs
`run-all`	`run --all`	Migration
`--terragrunt-*` flags	Unprefixed flags	CLI Reference
`TERRAGRUNT_*` env vars	`TG_*` env vars	CLI Reference

Resources

Templates - MUST Read Before Generating

Configuration Type	Template File	When to Read
Root configuration	`assets/templates/root/terragrunt.hcl`	Before generating any root.hcl
Child module	`assets/templates/child/terragrunt.hcl`	Before generating any child module
Standalone module	`assets/templates/module/terragrunt.hcl`	Before generating standalone modules
Stack file	`assets/templates/stack/terragrunt.stack.hcl`	Before generating stacks
Catalog unit	`assets/templates/catalog/terragrunt.hcl`	Before generating catalog units

References

Reference	Content	When to Read
`references/common-patterns.md`	All generation patterns with examples	Always, before generating
`../devops-skills:terragrunt-validator/references/best_practices.md`	Comprehensive best practices	Always, before generating

Official Documentation

Common Issues

Root.hcl Cannot Find env.hcl

Symptom:

Error: Attempt to get attribute from null value
  on ./root.hcl line X:
  This value is null, so it does not have any attributes.

Cause: Root.hcl is trying to read env.hcl via find_in_parent_folders("env.hcl"), but env.hcl doesn't exist at the root level.

Solution: Make root.hcl environment-agnostic:

# DON'T do this in root.hcl for multi-environment setups:
locals {
  env_vars = read_terragrunt_config(find_in_parent_folders("env.hcl"))  # FAILS
}

# DO use static values or get_env():
generate "provider" {
  path      = "provider.tf"
  if_exists = "overwrite_terragrunt"
  contents  = <<EOF
provider "aws" {
  region = "us-east-1"  # Static value, or use get_env("AWS_REGION", "us-east-1")
}
EOF
}

Provider Conflict with Registry Modules

When using Terraform Registry modules (e.g., tfr:///terraform-aws-modules/vpc/aws), they may define their own required_providers block. This can conflict with provider configuration generated by root.hcl.

Symptoms:

Error: Duplicate required providers configuration

Solutions:

Remove conflicting generate block - If using registry modules that manage their own providers, avoid generating duplicate required_providers:

# In root.hcl - only generate provider config, not required_providers
generate "provider" {
  path      = "provider.tf"
  if_exists = "overwrite_terragrunt"
  contents  = <<EOF
provider "aws" {
  region = "us-east-1"
}
EOF
}

Use if_exists = "skip" - Skip generation if file already exists:

generate "versions" {
  path      = "versions.tf"
  if_exists = "skip"  # Don't overwrite module's versions.tf
  contents  = "..."
}

Clear cache - If conflicts persist after fixes:
```
rm -rf .terragrunt-cache
terragrunt init
```

Feature Flag Validation Errors

If you see Unknown variable; There is no variable named "local" in feature blocks, ensure defaults are static values (see Feature Flags section above).

Child Module Cannot Find env.hcl