Terraform Best Practices: The Definitive Guide
A comprehensive guide to enterprise-grade Terraform, covering project structure, state management, modules, CI/CD, and security best practices.
📋 Prerequisites
- A solid understanding of the basic Terraform workflow (
init,plan,apply). - Experience writing and applying basic Terraform configurations.
- Familiarity with a version control system (VCS) like Git.
- Access to at least one cloud provider account (AWS, Azure, or GCP).
What You'll Learn
- How to structure your Terraform projects for scalability.
- Best practices for managing Terraform state remotely and securely.
- How to effectively use and create modules for reusable infrastructure.
- Strategies for integrating Terraform into a CI/CD pipeline.
- Core security principles for writing and managing Terraform code.
🏷️ Topics Covered
Project Structure: A Foundation for Scale
A well-organized project structure is the most important factor for long-term success with Terraform. Avoid putting all your .tf files in a single directory. A scalable structure isolates environments and components, reducing complexity and blast radius.
Recommended Repository Structure
This structure separates environments at the top level, with each environment consuming a shared set of modules.
/terraform-repo
├── /environments
│ ├── /dev
│ │ ├── main.tf # Deploys modules for dev
│ │ ├── variables.tf
│ │ └── terraform.tfvars
│ ├── /staging
│ │ ├── main.tf # Deploys modules for staging
│ │ ├── variables.tf
│ │ └── terraform.tfvars
│ └── /prod
│ ├── main.tf # Deploys modules for prod
│ ├── variables.tf
│ └── terraform.tfvars
│
└── /modules
├── /aws-vpc
│ ├── main.tf
│ ├── variables.tf
│ └── outputs.tf
└── /aws-rds
├── main.tf
├── variables.tf
└── outputs.tf
State Management: The Single Source of Truth
The Terraform state file is a critical component that maps your code to real-world resources. Managing it correctly is non-negotiable for team collaboration.
🚨 Never Commit State Files to Git
The terraform.tfstate file often contains sensitive data and is meant to be a dynamic record of your infrastructure, not a versioned file. Always add *.tfstate* and .terraform/ to your .gitignore file.
Use a Remote Backend
A remote backend, such as an AWS S3 bucket, Azure Storage Account, or Terraform Cloud, provides a centralized, secure location for your state files. It is essential for team collaboration.
Example: S3 Remote Backend Configuration
# In your environments/dev/main.tf
terraform {
backend "s3" {
bucket = "my-company-terraform-state"
key = "dev/network/terraform.tfstate"
region = "us-east-1"
dynamodb_table = "terraform-state-locks" # For state locking
encrypt = true
}
}Key Features:
- State Locking: Using a DynamoDB table prevents multiple people from running
applyat the same time, avoiding state corruption. - Encryption: Ensures your state file is encrypted at rest.
Modules: The Building Blocks of Reusability
Modules are the key to writing reusable, maintainable, and versioned infrastructure components. Instead of copying and pasting your VPC configuration for every environment, you should define it once in a module and reuse it.
Keep Modules Focused
A good module has a clear and limited purpose. Create a module for a VPC, another for an RDS database, and another for an ECS service. Avoid creating giant "monolith" modules.
Use a Versioned Source
Always source modules from a versioned Git repository or a module registry like the Terraform Registry or a private registry in Terraform Cloud. This ensures that changes to a module don't unexpectedly break your configurations.
Expose Outputs, Not Resources
Use module outputs to expose only the necessary information (like a VPC ID or a database endpoint). This creates a clean interface and hides the internal complexity of the module.
CI/CD Integration: Automating Your Workflow
Automating your Terraform workflow in a CI/CD pipeline ensures that every change is consistently tested, reviewed, and applied, providing a complete audit trail.
Example: GitHub Actions Workflow for PRs
This workflow automatically runs terraform plan on every pull request and posts the output as a comment, allowing for safe and effective code reviews.
name: 'Terraform Plan on PR'
on:
pull_request:
paths:
- 'environments/dev/**'
jobs:
terraform:
name: 'Terraform'
runs-on: ubuntu-latest
defaults:
run:
working-directory: ./environments/dev
steps:
- name: Checkout
uses: actions/checkout@v4
- name: Setup Terraform
uses: hashicorp/setup-terraform@v3
- name: Terraform Init
run: terraform init
- name: Terraform Plan
id: plan
run: terraform plan -no-color
- name: Add Plan to PR Comment
uses: actions/github-script@v6
with:
script: |
const output = `#### Terraform Plan 📖\`\`\`\n\${{ steps.plan.outputs.stdout }}\n\`\`\``;
github.rest.issues.createComment({
issue_number: context.issue.number,
owner: context.repo.owner,
repo: context.repo.repo,
body: output
});Security Best Practices
Securing your infrastructure starts with securing the code that defines it. Follow these core principles to minimize risk.
💡 Key Security Principles
- Least Privilege IAM: The credentials used by Terraform in your CI/CD pipeline should only have the permissions necessary to manage the resources in its scope. Avoid using long-lived administrator keys.
- Scan Your Code: Integrate an IaC scanner like Checkov or tfsec into your pipeline to automatically check for common security misconfigurations (e.g., public S3 buckets, unrestricted security groups).
- Manage Secrets Securely: Never commit secrets or sensitive data to your Git repository. Use a secrets management tool like HashiCorp Vault, AWS Secrets Manager, or your CI/CD platform's secret store.
- Use the Latest Provider Versions: Keep your Terraform provider versions up-to-date to benefit from the latest features and security patches. Use version pinning to avoid unexpected changes.