Terragrunt Server

A Model Context Protocol (MCP) server that provides comprehensive Terragrunt documentation and tooling integration for AI assistants like GitHub Copilot in VS Code.

Overview

This MCP server enables AI assistants to access and search the complete Terragrunt documentation, providing intelligent assistance for working with Terragrunt configurations, CLI commands, and HCL syntax. It features a robust caching system with network resilience and multiple fallback mechanisms.

New: Multi-mode architecture with 60-94% token overhead reduction for optimized AI assistant integration. Choose the mode that fits your workflow: CORE (docs), CONFIG (generation), GUIDANCE (troubleshooting), OBSERVABILITY (metrics), or FULL (all tools).

Features

📚 Documentation Access

• Live Documentation: Automatically fetches the latest Terragrunt documentation via llms.txt in a single HTTP request
• Indexed Search: Metadata-indexed architecture for efficient search with full content available on demand
• Smart Caching: Two-tier caching system (in-memory + disk) with 24-hour refresh cycle
• Network Resilience: Retry mechanism with exponential backoff (3 retries, up to 10s delay)
• Multiple Fallbacks: Network → Disk cache → Stale cache → Local fixture (for offline/CI use)
• Fast Search: Metadata-first search (title/section/URL) with full-text content fallback
• Organized Sections: Browse documentation by categories (getting-started, reference, features, etc.)
• Persistent Cache: Cache survives server restarts (stored in .cache/terragrunt-docs/)

See Lazy Loading Documentation for performance optimization details.

⚙️ Configuration Generator

• Tiered Templates: Essential (4-5 vars) and Advanced (9-12 vars) backend templates
• Multi-Cloud Support: AWS S3, Azure Blob Storage, GCP GCS backends
• Advanced Features: KMS encryption, cross-account access, managed identity, service account impersonation
• Mustache Conditionals: Smart rendering includes only provided options
• Two-Tier Validation: Regex-based (fast) + optional Terragrunt CLI validation (accurate)
• Custom Templates: Extend with organization-specific templates

See Advanced Backend Templates for enterprise configuration options.

🔧 Available Tools

8 consolidated tools for comprehensive Terragrunt assistance:

• 7 core tools (tools 1-7): Documentation, functions, CLI, HCL reference, guidance, config generation, error diagnosis
• 1 observability tool (tool 8): Server metrics and monitoring

1. search_docs - Unified Documentation Search

Unified tool for all documentation search needs - semantic search, browsing sections, retrieving content, and finding code examples.

• Parameters:
  • mode (string, optional): Operation mode - search, list, section, or examples (default: search)
  • query (string, conditional): Search query text (required for search mode, optional for examples)
  • section (string, conditional): Section name (required for section mode)
  • detailLevel (string, optional): summary or full (default: summary)
  • Additional mode-specific parameters (page, pageSize, limit, advanced, category, etc.)
• Modes:
  • search: Semantic search across all documentation
  • list: List available documentation sections
  • section: Get docs from a specific section
  • examples: Find code examples and patterns (supports advanced curated examples)
• Use cases: All doc-related tasks including search, browsing, section retrieval, and code examples

2. function_reference - Built-in Function Reference

Get function details OR list all functions - unified tool for Terragrunt built-in function documentation.

• Get Mode (when function_name provided):
  • function_name (string): Function name (e.g., "path_relative_to_include", "get_env")
  • mode (string, optional): Detail level - summary or full (default: summary)
  • include_examples (boolean, optional): Include code examples (default: true)
  • Returns: Complete function metadata including signature, parameters, return type, examples
• List Mode (when no function_name):
  • category (string, optional): Filter by category (e.g., "path", "aws", "environment")
  • search (string, optional): Search in function names and descriptions
  • page (number, optional): Page number (default: 1)
  • pageSize (number, optional): Results per page (default: 20)
  • Returns: Array of functions with name, signature, category, and description
• Use cases: Looking up specific functions, discovering available functions, browsing by category

3. cli_reference - CLI Command Reference

Get command help OR list commands - unified tool for Terragrunt CLI command documentation.

• Get Mode (when command provided):
  • command (string): Command name (e.g., "plan", "apply", "run-all", "hclfmt")
  • Returns: Command documentation with usage, options, and examples
• List Mode (when no command):
  • category (string, optional): Filter by category (main, backend, stack, catalog, discovery, configuration, shortcut)
  • search (string, optional): Search in command names and descriptions
  • page (number, optional): Page number (default: 1)
  • pageSize (number, optional): Commands per page (default: 20)
  • Returns: Array of commands with name, category, and description
• Use cases: Learning command syntax, understanding command options, CLI troubleshooting, discovering available commands

4. get_hcl_config_reference - HCL Configuration Reference

Get documentation for HCL configuration blocks used in terragrunt.hcl files.

• Parameters:
  • config (string, optional): Block name (e.g., "terraform", "remote_state", "dependency", "inputs", "generate", "locals")
  • category (string, optional): Filter blocks by category (core, modules, generation, execution, iam, terraform)
  • listBlocks (boolean, optional): List all available HCL blocks (default: false)
• Returns: HCL block documentation with syntax, attributes, examples, and usage patterns
• Use cases: Writing terragrunt.hcl files, understanding configuration options, discovering available blocks

5. get_guidance - Best Practices & Comparisons

Get best practices, comparisons, or patterns for Terragrunt usage.

• Parameters:
  • query (string, optional): Topic, comparison, or scenario
  • type (string, optional): Guidance type - best-practices, comparison, or pattern
  • mode (string, optional): Detail level - summary or full (default: summary)
  • level (string, optional): Experience level - beginner, intermediate, or advanced
  • listAll (boolean, optional): List all available guidance (default: false)
• Returns: Structured recommendations with priority, rationale, examples, antipatterns, tradeoffs, and experience notes
• Use cases: Learning best practices, understanding patterns, avoiding common pitfalls, comparing approaches, getting experience-appropriate guidance

Example prompts:

"What are the best practices for state management?"
"Compare different approaches for module organization"
"Show me beginner-level dependency management practices"
"What patterns should I use for CI/CD with Terragrunt?"

6. build_config - Generate or Write Terragrunt Configuration

Generate OR write OR generate+write Terragrunt configurations - unified tool for configuration management.

• Generate Mode (when useCase provided, no content):
  • useCase (string): Configuration type - remote_state, provider_generation, dependencies, hooks, or inputs
  • options (object): Template variables (varies by use case and backend)
  • backend (string, optional): Backend type for remote_state - s3, azurerm, or gcs
  • tier (string, optional): Template tier - essential, advanced, or complete (default: essential)
  • strictValidation (boolean, optional): Enable strict validation (default: false)
  • Returns: Generated HCL configuration with explanation and next steps
• Write Mode (when content provided):
  • content (string): HCL content to write
  • path (string): File path where config should be written
  • overwrite (boolean, optional): Allow overwriting existing files (default: false)
  • createBackup (boolean, optional): Create backup before overwrite (default: true)
  • createParentDirs (boolean, optional): Create parent directories if missing (default: true)
  • Returns: Write confirmation with file path
• Generate+Write Mode (when useCase + write=true + path):
  • Combines both modes - generates configuration and writes to disk in one operation
  • Returns: Generated config + write confirmation
• Security: File writing disabled by default, requires explicit configuration (see File Writing Guide)
• Use cases: Quick project setup, learning HCL syntax, best practice configurations, saving generated configs, automating configuration updates

Example prompts:

"Generate a terragrunt config for S3 remote state in us-east-1"
"Write this configuration to /home/user/terraform/terragrunt.hcl"
"Generate and save an Azure backend configuration to my project"
"Show me how to set up dependencies between terragrunt modules"

7. diagnose_terragrunt_error - Error Diagnosis and Troubleshooting

Diagnose Terragrunt error messages and get actionable solutions, debugging steps, and relevant documentation links.

• Parameters:
  • error_message (string, required): The error message from Terragrunt to diagnose
  • command (string, optional): Command that was run (e.g., "apply", "plan")
  • version (string, optional): Terragrunt version
  • os (string, optional): Operating system
  • filePath (string, optional): File path where error occurred
  • module (string, optional): Module name
  • backend (string, optional): Backend type
  • maxMatches (number, optional): Maximum matches to return (default: 3)
  • minConfidence (number, optional): Minimum confidence score 0-1 (default: 0.3)
  • enableFuzzyMatching (boolean, optional): Enable fuzzy matching (default: true)
  • enrichWithDocs (boolean, optional): Enrich with documentation-sourced solutions (default: false)
• Returns: Matches with confidence scores, solutions, debugging steps, related errors, and documentation links (66 error patterns across 7 categories)
• Use cases: Troubleshooting errors, getting actionable solutions, finding relevant documentation

Example prompts:

"I'm getting this error: Error acquiring the state lock"
"Help me fix: Backend configuration changed since last init"
"Diagnose this terragrunt error and tell me how to fix it"

See the Troubleshooting Guide for detailed usage examples and best practices.

8. get_server_metrics - Server Metrics and Monitoring

Retrieve comprehensive performance metrics for the MCP server, including tool execution times, cache statistics, and error tracking.

• Parameters:
  • format (string, optional): Output format - "json" or "text" (default: "json")
  • filter (string, optional): Filter metrics by tool name prefix
  • reset (boolean, optional): Reset metrics after retrieval (default: false)
• Returns: Performance metrics including:
  • Tool execution counts and timings (min/max/avg latency)
  • Error rates and error types by tool
  • Cache hit/miss ratios and efficiency
  • Memory and performance trends
• Use cases: Performance monitoring, debugging slow operations, capacity planning, identifying optimization opportunities

Example prompts:

"Show me server metrics in text format"
"Get metrics for all 'get_' tools only"
"What's the cache hit rate and average latency?"
"Show me metrics and reset them after"

See the Metrics Collection Guide for detailed usage, reporting, and export options.

---

For complete tool documentation and examples, see Available Tools.

📖 Resources

• Complete documentation overview with section breakdown
• Individual documentation pages as separate resources
• Section-based documentation collections
• All content accessible through VS Code and Copilot

Server Modes

The Terragrunt MCP Server supports 5 operational modes to optimize token usage and reduce overhead for specific workflows. Each mode loads only the tools and dependencies needed for its use case.

Mode Overview

Mode	Tools	Token Overhead	Memory	Managers	Use Case
FULL	8	2,441 (baseline)	0.20 MB	12/12	All features, backward compatible
CORE	4	965 (-60%)	0.19 MB	4/12	Documentation & reference lookups
CONFIG	2	640 (-74%)	0.08 MB	6/12	Configuration generation
GUIDANCE	2	683 (-72%)	0.13 MB	4/12	Troubleshooting & best practices
OBSERVABILITY	1	155 (-94%)	0.04 MB	0/12	Metrics & monitoring only

Quick Mode Selection

Use CORE mode when:

• Looking up documentation quickly
• Exploring CLI commands and functions
• Learning Terragrunt basics
• Need reference information

Use CONFIG mode when:

• Generating Terragrunt configurations
• Working with HCL templates
• CI/CD automation pipelines
• Template-based workflows

Use GUIDANCE mode when:

• Debugging errors
• Getting best practices advice
• Troubleshooting deployments
• Learning patterns and comparisons

Use OBSERVABILITY mode when:

• Monitoring server performance
• Tracking usage metrics
• Minimal deployment footprint
• Metrics-only workflows

Use FULL mode when:

• Need multiple tool categories
• Exploratory workflows
• Backward compatibility required
• Uncertain which tools needed

Mode Performance

Verified performance metrics:

• Token reduction: 60-94% vs FULL mode
• Memory savings: 5-80% vs baseline
• Manager efficiency: 50-100% reduction
• Startup time: 1-4ms (negligible)
• Lazy loading: Confirmed working

See MODE_PERFORMANCE_VERIFIED.md for detailed benchmarks.

Installation

Option 1: Using Docker (Recommended)

The easiest way to get started is using the pre-built Docker image:

# Pull the latest image
docker pull olofdevopsninja/terragrunt-mcp-server:latest

# Run with Docker
docker run -i olofdevopsninja/terragrunt-mcp-server:latest

# Or use docker-compose
docker-compose up

See the Docker Deployment Guide for detailed instructions.

Option 2: From Source

1. Clone the repository

2. Install dependencies:

   npm install
   

3. Build the server:

   npm run build
   

VS Code Configuration

Using Docker Hub Image (Recommended)

FULL mode (all tools, default):

{
  "mcp.servers": {
    "terragrunt": {
      "command": "docker",
      "args": [
        "run",
        "-i",
        "--rm",
        "-v", "mcp-cache:/app/.cache",
        "olofdevopsninja/terragrunt-mcp-server:latest"
      ]
    }
  }
}

Specialized modes (optimized for specific use cases):

{
  "mcp.servers": {
    "terragrunt-docs": {
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-v", "mcp-cache:/app/.cache",
        "olofdevopsninja/terragrunt-mcp-server:latest",
        "--mode", "core"
      ]
    },
    "terragrunt-config": {
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-v", "mcp-cache:/app/.cache",
        "olofdevopsninja/terragrunt-mcp-server:latest",
        "--mode", "config"
      ]
    }
  }
}

Using Local Build

FULL mode:

{
  "mcp.servers": {
    "terragrunt": {
      "command": "node",
      "args": ["dist/index.js"],
      "cwd": "/absolute/path/to/terragrunt-mcp-server"
    }
  }
}

Specialized modes using CLI wrappers:

{
  "mcp.servers": {
    "terragrunt-docs": {
      "command": "node",
      "args": ["bin/terragrunt-mcp-core"],
      "cwd": "/absolute/path/to/terragrunt-mcp-server"
    },
    "terragrunt-config": {
      "command": "node",
      "args": ["bin/terragrunt-mcp-config"],
      "cwd": "/absolute/path/to/terragrunt-mcp-server"
    }
  }
}

Alternative: Direct mode flag:

{
  "mcp.servers": {
    "terragrunt-core": {
      "command": "node",
      "args": ["dist/index.js", "--mode", "core"],
      "cwd": "/absolute/path/to/terragrunt-mcp-server"
    }
  }
}

1. Restart VS Code to activate the MCP server

2. Verify installation: Ask GitHub Copilot: "Search Terragrunt docs for getting started"

Usage with GitHub Copilot

Once configured, interact with Terragrunt documentation directly through Copilot in VS Code. The server provides intelligent context for all your Terragrunt questions.

Example Prompts by Category

General Documentation Search

• "Search for Terragrunt documentation about dependencies"
• "Show me the getting started guide for Terragrunt"
• "What are the available configuration options in Terragrunt?"
• "How do I use remote state with Terragrunt?"
• "Find documentation about Terragrunt generate blocks"

CLI Command Help

• "What options are available for the terragrunt plan command?"
• "How do I use terragrunt run-all?"
• "Show me help for the hclfmt command"
• "What does terragrunt validate-inputs do?"

HCL Configuration Reference

• "Show me how to configure the terraform block in terragrunt.hcl"
• "What are the available remote_state options?"
• "How do I use the dependency block?"
• "What attributes can I use in the inputs block?"

Code Examples

• "Show me examples of using dependencies in Terragrunt"
• "Find code snippets for remote state configuration"
• "What are some examples of before_hook usage?"
• "Show me how to use generate blocks with examples"

Built-in Functions

• "Show me documentation for the path_relative_to_include function"
• "What parameters does get_env accept?"
• "List all AWS-related Terragrunt functions"
• "What built-in functions are available for working with files?"
• "Search for functions related to environment variables"
• "How do I use find_in_parent_folders?"

Advanced Usage

• "Compare different approaches for Terragrunt module organization"
• "Show me best practices for Terragrunt project structure"
• "Explain the difference between dependency and dependencies blocks"
• "What's the recommended way to handle environment-specific configurations?"

Project Structure

terragrunt-mcp-server/
├── src/
│   ├── index.ts                 # MCP server entry point
│   ├── handlers/
│   │   ├── tools.ts             # Tool execution handlers (7 consolidated tools)
│   │   └── prompts.ts           # Prompt templates (future)
│   ├── terragrunt/
│   │   ├── docs.ts              # Documentation fetching and caching
│   │   ├── functions.ts         # Built-in functions manager
│   │   ├── cli-commands.ts      # CLI commands manager
│   │   ├── hcl-blocks.ts        # HCL configuration blocks manager
│   │   ├── best-practices.ts    # Best practices analyzer
│   │   ├── generator.ts         # Configuration generator
│   │   ├── file-writer.ts       # Secure file writing
│   │   ├── error-patterns.ts    # Error diagnosis patterns
│   │   ├── config.ts            # Configuration management
│   │   └── utils.ts             # Utility functions
│   └── types/
│       ├── mcp.ts               # MCP protocol type definitions
│       └── terragrunt.ts        # Terragrunt-specific types
├── test/
│   ├── unit/                    # Unit tests (Vitest)
│   ├── integration/             # Integration tests
│   ├── performance/             # Performance benchmarks
│   └── edge-cases/              # Edge case validation
├── fixtures/
│   └── terragrunt-docs-fixture.json  # Offline documentation cache
├── .cache/                      # Auto-generated cache (gitignored)
│   └── terragrunt-docs/
│       ├── docs-cache.json      # Cached documentation (~1.1MB)
│       └── metadata.json        # Cache timestamps
├── docs/                        # Comprehensive documentation
├── schemas/                     # JSON schemas
├── package.json                 # Node.js dependencies
├── tsconfig.json                # TypeScript configuration
└── README.md                    # This file

Key Files

• src/index.ts: Main entry point that initializes the MCP server with stdio transport
• src/handlers/tools.ts: Implements all 8 consolidated tools for documentation access
• src/terragrunt/docs.ts: Core documentation manager with caching, retry logic, and fallbacks
• test/: Comprehensive test suite with unit, integration, and performance tests

Development

Available Scripts

npm run build          # Compile TypeScript to dist/
npm run dev            # Run in development mode with ts-node
npm start              # Run compiled server from dist/
npm run lint           # Check code style with ESLint
npm run lint:fix       # Auto-fix linting issues
npm test               # Run all tests (Jest)
npm run test:server    # Run integration tests

Testing

The project includes comprehensive test coverage (363 tests):

• Unit Tests (160 tests): Core functionality validation
  • Functions Manager (21 tests)
  • Docs Manager (67 tests)
  • Error Handling (24 tests)
  • Resource Handler (24 tests)
  • Tool Handler (24 tests)
• Integration Tests (164 tests): End-to-end tool and resource testing
  • Functions Tools Integration (23 tests)
  • MCP Protocol Compliance (68 tests)
  • Edge Case Validation (48 tests)
  • Server Integration (24 tests)
  • Functions Tools (legacy .js) (1 test)
• Performance Tests (39 tests): Benchmark critical operations
  • Large result sets, search performance, concurrent operations
  • Cache efficiency, memory usage monitoring
  • Function lookup performance benchmarks

Running Tests Locally

npm test                          # Run all tests (~92 seconds)
npm run test:server              # Integration tests only
npm test -- test/unit            # Unit tests only
npm test -- test/performance     # Performance benchmarks
npm test -- test/integration     # All integration tests

GitHub Actions Workflows

Two CI/CD workflows are available:

1. Automatic Tests (.github/workflows/test.yml):

   • Runs on all pull requests
   • Tests on Node.js 18 and 20
   • Generates coverage reports
   • Uses npm caching for speed

2. Manual Tests (.github/workflows/manual-test.yml):

   • Manual trigger via GitHub UI
   • Choose specific test suite:
     • All tests
     • Unit tests
     • Integration tests
     • Performance tests
     • Edge case tests
     • MCP protocol tests
     • Error handling tests
   • Uploads test artifacts
   • Generates test summaries

Test Documentation

For detailed testing information, see:

• Performance Testing Guide
• Edge Cases Testing Guide
• MCP Protocol Compliance

Docker Support

Build and run in Docker for isolated testing:

# Build Docker image
npm run docker:build

# Run with docker-compose
npm run docker:compose:up
npm run docker:compose:logs
npm run docker:compose:down

See DOCKER.md for detailed Docker usage.

Contributing

See CONTRIBUTING.md for development guidelines and contribution process.

Technical Architecture

MCP Protocol Implementation

This server implements the Model Context Protocol (MCP) using the official SDK (@modelcontextprotocol/sdk). It provides:

• Stdio Transport: Direct integration with VS Code and other MCP clients
• Tool Handlers: Eight consolidated tools for comprehensive Terragrunt assistance
• Tool-Only Architecture: Simplified design with no MCP resources (v0.5.0+)
• Prompt Handlers: Future support for guided workflows

Documentation Caching System

The TerragruntDocsManager implements a sophisticated multi-tier caching strategy:

1. In-Memory Cache: Fast access to frequently used documentation
2. Disk Cache: Persistent storage in .cache/terragrunt-docs/ (~1.1MB)
3. 24-Hour Expiry: Automatic refresh to keep documentation current
4. Stale Cache Fallback: Uses expired cache when network fails
5. Local Fixture: Embedded documentation for complete offline support

Network Resilience

Built-in retry mechanism with exponential backoff:

• 3 retry attempts with increasing delays (1s → 2s → 4s)
• 10-second maximum delay to prevent excessive waiting
• Graceful degradation through multiple fallback layers
• CI/Test-friendly with deterministic fixture fallback

Web Scraping

Uses Cheerio to parse the official Terragrunt documentation site:

• Extracts all documentation pages from https://terragrunt.gruntwork.io/docs/
• Preserves document structure (sections, titles, URLs)
• Cleans HTML content for better AI consumption
• Updates automatically based on cache expiry

Version History

See CHANGELOG.md for detailed version history and migration guides.

Current Version: 0.5.0

• 8 consolidated tools (simplified from 11)
• Tool-only architecture (resources removed)
• Multi-tier caching with network resilience
• Docker support
• Comprehensive test coverage

License

This project is licensed under the MIT License. See the LICENSE file for details.

Related Resources

• Model Context Protocol Documentation
• Terragrunt Official Documentation
• GitHub Repository
• Setup Guide
• Docker Guide