Terraform Best Practices for AWS Infrastructure

Introduction

Terraform has become the de facto tool for provisioning AWS infrastructure as code. But as projects grow, poorly structured Terraform codebases become difficult to maintain, review, and scale. Following established best practices from the start saves significant refactoring effort later.

This guide covers the patterns and conventions that experienced infrastructure teams rely on to keep their Terraform AWS projects manageable, secure, and collaborative.

Remote State with S3 and DynamoDB

Never store Terraform state locally. Use an S3 backend with DynamoDB locking to enable team collaboration and prevent concurrent modifications:

terraform {
  backend "s3" {
    bucket         = "mycompany-terraform-state"
    key            = "production/vpc/terraform.tfstate"
    region         = "eu-west-1"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }
}

Create the state bucket with versioning enabled so you can recover from accidental state corruption:

aws s3api create-bucket \
  --bucket mycompany-terraform-state \
  --region eu-west-1 \
  --create-bucket-configuration LocationConstraint=eu-west-1

aws s3api put-bucket-versioning \
  --bucket mycompany-terraform-state \
  --versioning-configuration Status=Enabled

Module Design Principles

Structure reusable modules with clear inputs, outputs, and documentation:

modules/
├── vpc/
│   ├── main.tf
│   ├── variables.tf
│   ├── outputs.tf
│   └── README.md
├── ecs-service/
│   ├── main.tf
│   ├── variables.tf
│   └── outputs.tf

Keep modules focused on a single resource group. A VPC module should create the VPC, subnets, route tables, and NAT gateways — but not the EC2 instances or RDS databases that live inside it. Use variable blocks with descriptions, types, and validation rules:

variable "vpc_cidr" {
  description = "CIDR block for the VPC"
  type        = string
  default     = "10.0.0.0/16"

  validation {
    condition     = can(cidrhost(var.vpc_cidr, 0))
    error_message = "Must be a valid CIDR block."
  }
}

Environment Separation

Use separate directories per environment rather than Terraform workspaces for production workloads:

environments/
├── production/
│   ├── main.tf
│   ├── terraform.tfvars
│   └── backend.tf
├── staging/
│   ├── main.tf
│   ├── terraform.tfvars
│   └── backend.tf

This ensures that a terraform apply in staging can never accidentally affect production. Each environment references the same modules but with different variable values.

CI/CD Integration

Run terraform plan on every pull request and require manual approval for terraform apply:

# GitHub Actions example
- name: Terraform Plan
  run: |
    terraform init
    terraform plan -out=tfplan -no-color
  env:
    AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
    AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}

Always use -out=tfplan to ensure the exact plan that was reviewed is what gets applied. For more on managing AWS environments, check our post on automated SSL certificate management. Learn how our AWS cloud management service can help you adopt these practices.

Well-structured Terraform code pays dividends as your AWS infrastructure scales. Remote state, modular design, environment separation, and CI/CD integration form the foundation of a maintainable infrastructure-as-code practice.