Terraform and OpenTofu with Dependabot

Terraform and OpenTofu configurations pull in providers and modules, and that list grows over time. Left unmanaged, those dependencies turn into a source of security risk and busywork. Dependabot watches them for you and opens pull requests when something needs updating. This post walks through the problems it solves and how to set it up.

At a Glance: Problems Solved by Dependabot

The Challenges of IaC Dependencies

Problem 1: The Persistent Threat of Security Vulnerabilities

Providers and modules, like any software, can have security flaws. Manually tracking advisories and patching across numerous IaC projects is often too slow, leaving your infrastructure exposed.

• Dependabot's Solution: Dependabot automates vulnerability detection by continuously scanning your Terraform and OpenTofu dependencies against known advisory databases. When a vulnerability is found, it can automatically generate a pull request to update to a secure version, drastically reducing your window of exposure and the manual effort involved in patching. This proactive stance is crucial for minimizing the risk of exploits.

Problem 2: The Drain of Manual Dependency Updates

Keeping dependencies current involves more than just security. New versions bring bug fixes, performance improvements, and new features. However, manually monitoring for these updates across all your projects is a time-consuming, repetitive task that diverts engineering resources.

• Dependabot's Solution: Dependabot automates the discovery of new versions for your providers and modules, creating pull requests for these updates as well. This frees up your team from the manual toil of checking changelogs and registries, allowing them to focus on higher-value infrastructure development and optimization.

Problem 3: Infrastructure Instability and Falling Behind

Outdated dependencies pose security risks and can lead to unstable infrastructure. Bugs in older versions can cause unexpected behavior, and as cloud provider APIs evolve, older providers might become incompatible or deprecated.

• Dependabot's Solution: By facilitating regular updates, Dependabot helps ensure your IaC configurations benefit from the latest bug fixes and maintain compatibility with evolving platform APIs. This contributes to more stable, reliable, and predictable infrastructure deployments, and ensures you can use the latest features offered by your chosen tools and platforms.

Problem 4: Compliance and Audit Trail Headaches

Many organizations must adhere to compliance standards that mandate timely patching and up-to-date software. Demonstrating this due diligence can be challenging without a systematic approach.

• Dependabot's Solution: The automated pull requests generated by Dependabot create a clear, auditable trail of dependency updates. This not only helps in meeting compliance requirements related to vulnerability management and software currency but also enforces a consistent, reviewable process for these critical changes.

Dependabot in Action: Configuration Examples

Setting up Dependabot for your Terraform or OpenTofu projects is straightforward.

1. dependabot.yml Configuration:

You configure Dependabot by adding a dependabot.yml file to the .github directory of your repository. Here's a basic example for Terraform/OpenTofu:

# .github/dependabot.yml
version: 2
updates:
  - package-ecosystem: "terraform"
    directory: "/" # Specify the directory where your .tf files are located
    schedule:
      interval: "daily" # How often to check for updates
    # Optional: Add labels to Dependabot PRs for better organization
    labels:
      - "dependencies"
      - "terraform"
      - "dependabot"
    # Optional: Assign specific reviewers to Dependabot PRs
    reviewers:
      - "your-github-username"
      - "your-team-alias"

2. Example: Provider Version Update in a .tf file:

Dependabot will create pull requests that modify your Terraform/OpenTofu configuration files to update dependency versions.

After Dependabot's Pull Request (example): Say a new, secure version 4.67.0 is available, and then later 5.33.0. Dependabot might propose:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.33" # Updated to a newer, recommended version
    }
  }
}

(Note: The exact version Dependabot suggests will depend on your existing constraints, the type of update (security or version), and your dependabot.yml configuration.)

Before Dependabot's Update (e.g., versions.tf or main.tf):

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0" # An older version constraint
    }
  }
}

Once a pull request is created, your team can review the changes, run any CI/CD checks (like tofu plan or terraform plan), and then merge it. After merging, you'll typically run tofu init -upgrade or terraform init -upgrade to update your .terraform.lock.hcl file.

A More Secure and Efficient IaC Workflow

Dependabot takes the repetitive parts of dependency management off your plate: spotting vulnerable versions, checking for new releases, and leaving a paper trail of every update. Adding it to a Terraform or OpenTofu repo is a small change that keeps your providers and modules current without anyone having to remember to check.