Maintaining Terraform Module Health with Dependabot and Scalr

Terraform modules are the building blocks of most deployments, but they need upkeep, and platform teams usually carry that work. This post covers the tools and methods that keep modules healthy, whether your infrastructure team is two people or two hundred. The approach pairs the Scalr module registry with Dependabot and pull-request-based updates, so the modules you ship stay secure and current.

Components

Before we get into the solution, I want to cover a few other components that come up later in the post:

• Dependabot - Dependabot is GitHub's automated dependency update tool that scans repositories for outdated dependencies and automatically creates pull requests to update them. It helps development teams stay current with security patches and new version updates by monitoring package manifests and alerting teams when dependencies need attention.
• Scalr - Scalr is a Terraform automation and collaboration (TACO) platform that provides organizations with a centralized approach for managing Terraform. Platform teams can ensure they have control over the ecosystem while enabling self-service for development teams.
• Private Module Registry - A module registry allows organizations to publish approved and version-controlled modules for use by their development teams. This helps ensure the organization's security and coding standards are followed by all teams and it helps the developer experience as they are able to use the Terraform modules as building blocks rather than creating the Terraform code themselves.

What is Terraform Module Health and Why Does it Matter?

Terraform module health is the overall quality, maintainability, and reliability of your infrastructure-as-code components. Like any software, modules accumulate technical debt over time. Dependencies age, security vulnerabilities surface, and cloud provider services change underneath them. Keeping modules healthy is what keeps your infrastructure secure and aligned with current practices. The reverse is also true: an outdated module can introduce compatibility problems, performance issues, or security risks that spread through everything built on it. Skip the maintenance and you tend to pay for it later in emergency fixes and unplanned outages, while teams that watch module health can plan updates into a maintenance window instead. Organizations with mature DevOps practices usually run automated scanning that tracks things like dependency freshness, code quality, security posture, and provider compatibility, so their infrastructure holds up as requirements and technologies shift.

Versioning modules in a private registry helps a lot here. A versioned registry gives teams a controlled place to manage module lifecycles, keep backward compatibility intact, and hand consumers a clear upgrade path. Once modules carry versions in one central registry, you can see which infrastructure components are running outdated versions and prioritize the maintenance that matters. The registry becomes a single source of truth, so there's no guessing about which version a given environment or project should use. It also makes automated testing across versions practical, so teams can confirm an update won't break existing infrastructure before they release it. The net effect is that module management stops being reactive and becomes predictable.

How Does Scalr and Dependabot Help?

Scalr and Dependabot cover the module-health work between them, and most of it runs without anyone watching. Here is how the pieces fit:

Scalr provides a private module registry where organizations can store and version their Terraform modules, while Dependabot automatically scans these modules for new versions. When it finds an update, Dependabot opens a pull request to bump the module references in your Terraform code, so you're always on the latest version. That takes most of the manual work out of keeping the Terraform configuration files current.

Scalr also reports on Terraform module usage across workspaces, so teams can see which modules are used where, check that they're following organizational standards, and gauge how well their module strategy is working. The reporting makes it easy to spot workspaces that probably aren't using Dependabot, since their Terraform module version shows up out of date.

Implementation

Before working through this, ensure you have an account in scalr.io and GitHub.

Step 1: Obtain a fine-grained Scalr API access token

First, you need to create a custom role with minimal access to the Scalr API. To read all modules (both from the account and environment scopes), the API key has to be granted the following permissions:

1. Go to Security > IAM > Roles.
2. Click on the "New role"
3. Enter a role name, e.g. Dependabot
4. Click on the "Add permissions" and add the following permissions: environments:read and modules:read

Create a service account and assign the role from the previous step:

1. Go to Security > IAM > Service Accounts.
2. Click on the "New service account"
3. Enter a name, e.g. dependabot
4. Click on "Grant access", select the role selected in the previous step, and keep "Grant On" as "Account".
5. Optionally, set owners of the service account. More about owners you can read here.

After a service account is created, generate the API access token by clicking on the Generate token.

Step 2: Store the Scalr API Token in GitHub Secrets

1. Navigate to your repository on GitHub.
2. Go to Settings > Secrets and variables > Dependabot.
3. Click New repository secret.
4. Add the following secret: Name: SCALR_REGISTRY_TOKEN, Value: Your Scalr API token from the previous step.
5. Save the secret.

Step 3: Configure .github/dependabot.yml

Create or update the .github/dependabot.yml file in your repository with the following content:

version: 2
 
updates:
  - package-ecosystem: "terraform"
    directory: "/"  # Adjust if your Terraform code is in a subdirectory
    schedule:
      interval: "weekly" # Options: daily, weekly, monthly
    registries:
      - scalr-private-registry
 
registries:
  scalr-private-registry:
    type: "terraform-registry"
    url: "https://your-account.scalr.io"
    token: "${{secrets.SCALR_REGISTRY_TOKEN}}"

Further Information:

• package-ecosystem: "terraform" instructs Dependabot to check Terraform dependencies.
• directory: "/" specifies where the Terraform code is located. Add multiple entries if needed for subdirectories.
• schedule.interval: "weekly" defines how often Dependabot checks for updates.
• The registries section configures Dependabot to authenticate with Scalr using the API token.

Step 4: Commit and Push Changes

1. Add the .github/dependabot.yml file to your repository.
2. Commit and push the changes.
3. Navigate to Pull Requests > Dependabot in GitHub to verify that Dependabot is fetching updates.

The next time a new version is pushed, you will see that Dependabot will notice the change and automatically create the pull request:

Summary

Pairing Scalr's private module registry with Dependabot's scanning gives you a setup that watches your Terraform modules for outdated dependencies and security vulnerabilities on its own. When a new version lands, Dependabot identifies it and opens a pull request with the change log attached, so nobody has to track module versions by hand across the infrastructure. With that running, developers get a nudge when their Terraform code needs an update, and the platform team no longer has to chase anyone down to get it applied.