IaC CI/CD: Terraform & Terragrunt Pipelines

Infrastructure as Code without CI/CD is just documentation. Automating Terraform through pipelines — plan on pull request, apply on merge — provides confidence that infrastructure changes are reviewed, tested, and consistently applied. Terragrunt adds DRY configuration management on top, reducing duplication across environments.

Key Takeaways

• Pipeline stages: fmt → validate → plan (on PR) → apply (on merge to main)
• Terragrunt reduces environment duplication by generating backend and provider configurations from shared templates
• Plan output should be posted as a PR comment for review — infrastructure changes get the same rigor as code changes
• State is managed per environment and per component to limit blast radius
• OIDC authentication eliminates the need for static cloud credentials in CI/CD

Quick Overview

A typical Terraform CI/CD pipeline in GitHub Actions runs terraform fmt -check and terraform validate on every push. On a pull request, it runs terraform plan and posts the output as a PR comment. When the PR merges, it runs terraform apply -auto-approve against the plan. For multi-environment setups, the pipeline targets different directories or Terragrunt configurations based on the branch or trigger.

Terragrunt simplifies this by using a terragrunt.hcl hierarchy. Root configurations define common settings (remote state backend, provider versions). Child configurations in environment directories inherit these automatically, keeping configurations DRY while maintaining separate state files per component and environment.

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Read the full guide: IaC CI/CD: Terraform & Terragrunt Pipelines → — includes complete GitHub Actions workflow, Terragrunt directory structures, and plan/apply patterns.