---
title: Patcher
description: Automated dependency updates for your Terragrunt modules and configurations.
slug: terragrunt-scale/patcher
sidebar:
  order: 5
---

import { Aside } from '@astrojs/starlight/components';

Patcher is the dependency management component of Terragrunt Scale. It automates the process of keeping your infrastructure modules up to date, including handling breaking changes.

## How It Works

1. Patcher scans your repositories for Terragrunt module/unit/stack references, and their current versions.
2. When new versions are available, it opens PRs with the updated version pins.
3. For breaking changes, Patcher applies code transformations (patches) to automate resolution of breaking changes, or generates documentation for changes that require manual intervention.

## Key Capabilities

- **Automated update PRs** — New module versions are surfaced as PRs on a configurable schedule, fitting into your existing review workflow.
- **Breaking change handling** — Patcher doesn't just bump versions. It applies code patches for breaking changes or clearly documents what manual steps are needed so you can safely stay up to date.
- **Environment promotion** — Roll out updates to dev first, then staging, then production, with promotion workflows between environments.
- **Stack awareness** — Detects updates within nested stacks and `terragrunt.stack.hcl` files, not just individual units.
- **Grouping modes** — Combine related updates into a single PR to reduce noise, or keep them separate for granular review.

## Two Modes of Operation

- **Ongoing updates** — A GitHub Action that continuously scans your repositories and opens PRs when new versions are available. This is the primary mode for day-to-day use.
- **Legacy upgrades** — An interactive CLI mode for bringing significantly outdated repositories up to current versions. Useful for one-time catch-up migrations.

## Supported Sources

Patcher works with any IaC source that Terragrunt supports, including:

- The Gruntwork IaC Library
- Your own internal IaC
- Open-source OpenTofu/Terraform modules
- Open-source Terragrunt units/stacks

<Aside type="tip" title="Full Documentation">

For setup instructions, patching tutorials, and configuration reference, see the [Gruntwork Patcher documentation](https://docs.gruntwork.io/2.0/docs/patcher/concepts/).

</Aside>
