terragrunt-validator

name	terragrunt-validator
description	Validate, lint, audit, or check Terragrunt .hcl/terragrunt.hcl files, stacks, modules, compliance. Use when this capability is needed.
metadata	{"author":"akin-ozer"}

Terragrunt Validator

Overview

This skill provides comprehensive validation, linting, and testing capabilities for Terragrunt configurations. Terragrunt is a thin wrapper for Terraform/OpenTofu that provides extra tools for keeping configurations DRY (Don't Repeat Yourself), working with multiple modules, and managing remote state.

Use this skill when:

• Validating Terragrunt HCL files (*.hcl, terragrunt.hcl, terragrunt.stack.hcl)
• Working with Terragrunt Stacks (unit/stack blocks, terragrunt stack generate/run)
• Performing dry-run testing with terragrunt plan
• Linting Terragrunt/Terraform code for best practices
• Detecting and researching custom providers or modules
• Debugging Terragrunt configuration issues
• Checking dependency graphs
• Formatting HCL files
• Running security scans on infrastructure code (Trivy, Checkov)
• Generating run reports and summaries

Terragrunt Version Compatibility

This skill is designed for Terragrunt 0.93+ which includes the new CLI redesign.

CLI Command Migration Reference

Deprecated Command	New Command
run-all	run --all
hclfmt	hcl fmt
hclvalidate	hcl validate
validate-inputs	hcl validate --inputs
graph-dependencies	dag graph
render-json	render --json -w
terragrunt-info	info print
plan-all, apply-all	run --all plan, run --all apply

Key Changes in 0.93+:

• terragrunt run --all replaces terragrunt run-all for multi-module operations
• terragrunt dag graph replaces terragrunt graph-dependencies for dependency visualization
• terragrunt hcl validate --inputs replaces validate-inputs for input validation
• HCL syntax validation via terragrunt hcl fmt --check or terragrunt hcl validate
• Full validation requires terragrunt init && terragrunt validate

If using an older Terragrunt version, some commands may need adjustment.

Core Capabilities

1. Comprehensive Validation Suite

Run the comprehensive validation script to perform all checks at once:

bash scripts/validate_terragrunt.sh [TARGET_DIR]

What it validates:

• HCL formatting (terragrunt hcl fmt --check)
• HCL input validation (terragrunt hcl validate --inputs)
• Terragrunt configuration syntax
• Terraform configuration validation
• Linting with tflint
• Security scanning with Trivy (or legacy tfsec)
• Dependency graph validation
• Dry-run planning

Environment variables:

• SKIP_PLAN=true - Skip terragrunt plan step
• SKIP_SECURITY=true - Skip security scanning (Trivy/tfsec)
• SKIP_LINT=true - Skip tflint linting
• SKIP_INIT=true - Skip terragrunt init before validation
• SKIP_BACKEND_INIT=true - Run init with -backend=false (useful in CI/offline)
• SOFT_FAIL_SECURITY=true - Report security findings without failing
• TG_STRICT_MODE=true - Enable strict mode (errors on deprecated features)

Example usage:

# Full validation
bash scripts/validate_terragrunt.sh ./infrastructure/prod

# Skip plan generation (faster)
SKIP_PLAN=true bash scripts/validate_terragrunt.sh ./infrastructure

# Only validate, skip linting and security
SKIP_LINT=true SKIP_SECURITY=true bash scripts/validate_terragrunt.sh

2. Custom Provider and Module Detection

Use the detection script to identify custom providers and modules that may require documentation lookup:

python3 scripts/detect_custom_resources.py [DIRECTORY] [--format text|json]

What it detects:

• Custom Terraform providers (non-HashiCorp)
• Remote modules (Git, Terraform Registry, HTTP)
• Provider versions
• Module versions and sources

Output formats:

• text - Human-readable report with search recommendations
• json - Machine-readable format for automation

When custom resources are detected:

CRITICAL: You MUST look up documentation for EVERY detected custom resource (both providers AND modules). Do NOT skip any. This is mandatory, not optional.

1. For custom providers:

   • Option A - WebSearch: Search for provider documentation
     • Query format: "{provider_source} terraform provider documentation version {version}"
     • Example: "mongodb/mongodbatlas terraform provider documentation version 1.14.0"
   • Option B - Context7 MCP (Preferred): Use Context7 for structured documentation lookup
     • Step 1: Resolve library ID: mcp__context7__resolve-library-id with provider name (e.g., "datadog terraform provider")
     • Step 2: REQUIRED - Fetch docs via mcp__context7__query-docs with the resolved library ID
     • Use queries like "authentication requirements" and "configuration examples"

2. For custom modules (EQUALLY IMPORTANT - DO NOT SKIP):

   • Terraform Registry modules:
     • Use Context7: mcp__context7__resolve-library-id with module name (e.g., "terraform-aws-modules vpc")
     • Then fetch docs with mcp__context7__query-docs
     • Or visit https://registry.terraform.io/modules/{source}/{version}
   • Git modules: Use WebSearch with the repository URL to find README or documentation
   • HTTP modules: Investigate the source URL for documentation
   • Pay attention to version compatibility with your Terraform/Terragrunt version

3. Documentation lookup workflow (MANDATORY for ALL detected resources):

   a) Run detect_custom_resources.py
   b) For EACH custom provider/module:
      - Note the exact version
      - Use Context7 MCP:
        1. mcp__context7__resolve-library-id with libraryName: "{provider/module name}"
        2. mcp__context7__query-docs with:
           - libraryId: "{resolved ID}"
           - query: "authentication requirements" (for auth requirements)
        3. mcp__context7__query-docs with:
           - libraryId: "{resolved ID}"
           - query: "configuration examples" (for setup requirements)
      - OR use WebSearch with version-specific queries
      - Review documentation for:
        * Required configuration blocks
        * Authentication requirements (API keys, credentials)
        * Available resources/data sources
        * Known issues or breaking changes in the version
   c) Apply learnings to validation/troubleshooting
   d) Document findings if issues are encountered
   

Example using Context7 MCP:

# 1. Detect custom resources
python3 scripts/detect_custom_resources.py ./infrastructure
# Output: Provider: datadog/datadog, Version: 3.30.0

# 2. Resolve library ID
mcp__context7__resolve-library-id with libraryName: "datadog terraform provider"
# Result: /datadog/terraform-provider-datadog

# 3. Fetch authentication docs (REQUIRED)
mcp__context7__query-docs with:
  libraryId: "/datadog/terraform-provider-datadog"
  query: "authentication requirements"

# 4. Fetch configuration docs
mcp__context7__query-docs with:
  libraryId: "/datadog/terraform-provider-datadog"
  query: "configuration examples"

Example using WebSearch:

# Detect custom resources
python3 scripts/detect_custom_resources.py ./infrastructure

# Then search for documentation:
# WebSearch: "datadog terraform provider 3.30.0 authentication configuration"
# WebSearch: "datadog terraform provider api_key app_key setup"

3. Step-by-Step Validation

For manual or granular validation, use these individual commands:

Format Validation

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

# To auto-fix formatting
terragrunt hcl fmt

Configuration Validation

# Check HCL syntax and formatting
terragrunt hcl fmt --check

# Note: In Terragrunt 0.93+, for deeper configuration validation,
# initialize and validate (requires actual resources/credentials):
# terragrunt init && terragrunt validate

Terraform Validation

# Initialize if needed
terragrunt init

# Validate
terragrunt validate

Linting with tflint

# Initialize tflint (if .tflint.hcl exists)
tflint --init

# Run linting
tflint --recursive

Security Scanning with Trivy (Recommended)

Note: tfsec has been merged into Trivy and is no longer actively maintained. Use Trivy for all new projects.

# Using Trivy (recommended)
trivy config . --severity HIGH,CRITICAL

# With tfvars file
trivy config --tf-vars terraform.tfvars .

# Exclude downloaded modules
trivy config --tf-exclude-downloaded-modules .

# Legacy: Using tfsec (deprecated)
tfsec . --soft-fail

Alternative: Security Scanning with Checkov

# Scan directory
checkov -d . --framework terraform

# Scan with specific checks
checkov -d . --check CKV_AWS_21

# Output as JSON
checkov -d . --output json

Dependency Graph Validation

# Note: graph-dependencies command replaced with 'dag graph' in Terragrunt 0.93+
# Validate and display dependency graph
terragrunt dag graph

# Visualize dependencies (requires graphviz)
terragrunt dag graph | dot -Tpng > dependencies.png

Dry-Run Planning

# Single module
terragrunt plan

# All modules (new syntax - Terragrunt 0.93+)
terragrunt run --all plan

# Legacy syntax (deprecated)
# terragrunt run-all plan

4. Multi-Module Operations

For projects with multiple Terragrunt modules, use run --all (replaces deprecated run-all):

# Validate all modules
terragrunt run --all validate

# Plan all modules
terragrunt run --all plan

# Apply all modules
terragrunt run --all apply

# Destroy all modules
terragrunt run --all destroy

# Format all HCL files
terragrunt hcl fmt

# With parallelism
terragrunt run --all plan --parallelism 4

# With strict mode (errors on deprecated features)
terragrunt --strict-mode run --all plan

# Or via environment variable
TG_STRICT_MODE=true terragrunt run --all plan

5. HCL Input Validation (New in 0.93+)

Validate that all required inputs are set and no unused inputs exist:

# Validate inputs
terragrunt hcl validate --inputs

# Show paths of invalid files
terragrunt hcl validate --show-config-path

# Combine with run --all to exclude invalid files
terragrunt run --all plan --queue-excludes-file <(terragrunt hcl validate --show-config-path || true)

6. Strict Mode

Enable strict mode to catch deprecated features early:

# Via CLI flag
terragrunt --strict-mode run --all plan

# Via environment variable (recommended for CI/CD)
export TG_STRICT_MODE=true
terragrunt run --all plan

# Check available strict controls
terragrunt info strict

Specific Strict Controls:

For finer-grained control, use --strict-control to enable specific controls:

# Enable specific strict controls
terragrunt run --all plan --strict-control cli-redesign --strict-control deprecated-commands

# Via environment variable (comma-separated)
TG_STRICT_CONTROL='cli-redesign,deprecated-commands' terragrunt run --all plan

# Available strict controls:
# - cli-redesign: Errors on deprecated CLI syntax
# - deprecated-commands: Errors on deprecated commands (run-all, hclfmt, etc.)
# - root-terragrunt-hcl: Errors when using root terragrunt.hcl (use root.hcl instead)
# - skip-dependencies-inputs: Improves performance by not reading dependency inputs
# - bare-include: Errors on bare include blocks (use named includes)

7. New CLI Commands (0.93+)

Render Configuration

# Render configuration to JSON
terragrunt render --json

# Render and write to file
terragrunt render --json --write

# Output goes to terragrunt.rendered.json

Info Print (replaces terragrunt-info)

# Get contextual information about current configuration
terragrunt info print

# Output includes:
# - config_path
# - download_dir
# - terraform_binary
# - working_dir

Find and List Units

# Find all units/stacks in directory
terragrunt find

# Output as JSON
terragrunt find --json

# Include dependency information
terragrunt find --json --dag

# List units (simpler output)
terragrunt list

Run Summary and Reports

# Run with summary output (default in newer versions)
terragrunt run --all plan

# Disable summary output
terragrunt run --all plan --summary-disable

# Generate detailed report file
terragrunt run --all plan --report-file=report.json

# CSV format report
terragrunt run --all plan --report-file=report.csv

8. Terragrunt Stacks (GA in v0.78.0+)

Terragrunt Stacks provide declarative infrastructure generation using terragrunt.stack.hcl files.

Stack File Structure

# terragrunt.stack.hcl
locals {
  environment = "dev"
  aws_region  = "us-east-1"
}

# Define a unit (generates a single terragrunt.hcl)
unit "vpc" {
  source = "git::[e-mail]:acme/infra-catalog.git//units/vpc?ref=v0.0.1"
  path   = "vpc"

  values = {
    environment = local.environment
    cidr        = "10.0.0.0/16"
  }
}

unit "database" {
  source = "git::[e-mail]:acme/infra-catalog.git//units/database?ref=v0.0.1"
  path   = "database"

  values = {
    environment = local.environment
    vpc_path    = "../vpc"
  }
}

# Include reusable stacks
stack "monitoring" {
  source = "git::[e-mail]:acme/infra-catalog.git//stacks/monitoring?ref=v0.0.1"
  path   = "monitoring"

  values = {
    environment = local.environment
  }
}

Stack Commands

# Generate stack (creates .terragrunt-stack directory)
terragrunt stack generate

# Generate stack without validation
terragrunt stack generate --no-stack-validate

# Run command on all stack units
terragrunt stack run plan
terragrunt stack run apply

# Clean generated stack directories
terragrunt stack clean

# Get stack outputs
terragrunt stack output

Stack Validation Control

Use no_validation attribute to skip validation for specific units:

unit "experimental" {