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In this lesson, we’ll deploy Amazon EC2 instances across multiple environments using a custom Terraform module and Terragrunt. By encapsulating compute configuration in a reusable module, we guarantee consistency, simplify management, and accelerate provisioning of our workloads. Our end-to-end workflow:
  1. Build a dedicated Terraform module for EC2 provisioning.
  2. Create Terragrunt configurations for each environment (development, production).
  3. Provide environment-specific variables (instance type, AMI ID, networking).
  4. Run terragrunt init, plan, and apply.
  5. Validate security groups, key pairs, and network settings.
The image shows a diagram for setting up EC2 resources with Terragrunt commands on the left and a shield icon representing considerations on the right.

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1. Custom Terraform Module

Create a folder structure under modules/ec2/:
FilePurpose
main.tfDefines aws_instance, security group attachments, user data, etc.
variables.tfDeclares inputs such as instance_type, ami_id, vpc_security_group_ids, key_name.
outputs.tfExposes attributes like public IP and instance ID.

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Example: variables.tf

variable "environment" {
  description = "Deployment environment (e.g., dev, prod)"
  type        = string
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
}

variable "ami_id" {
  description = "AMI ID for the instance"
  type        = string
}

variable "vpc_security_group_ids" {
  description = "List of security group IDs"
  type        = list(string)
}

variable "key_name" {
  description = "Key pair name for SSH access"
  type        = string
}
Make sure your AMI IDs match the target AWS region. You can automate lookup via the AWS Systems Manager Parameter Store.

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2. Terragrunt Configuration per Environment

Under each environment folder (environments/development/, environments/production/), define a terragrunt.hcl that points to the EC2 module and sets inputs: 
# environments/development/terragrunt.hcl
terraform {
  source = "../../modules/ec2"
}

inputs = {
  environment             = "development"
  instance_type           = "t3.micro"
  ami_id                  = "ami-0123456789abcdef0"
  vpc_security_group_ids  = ["sg-0123456789abcdef0"]
  key_name                = "dev-key-pair"
}
Repeat for production, adjusting values accordingly.
Avoid committing sensitive data (e.g., private SSH keys) to version control. Store critical secrets in a secure vault or use Terragrunt’s read_terragrunt_config to pull from encrypted sources.

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3. Deploying with Terragrunt

Within your chosen environment directory, execute: 
terragrunt init      # Initialize the Terraform working directory
terragrunt plan      # Preview infrastructure changes
terragrunt apply     # Provision EC2 instances as defined
After deployment, verify that your security groups, key pairs, and networking settings meet your organization’s standards.

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