NAT Instance Terraform Module

Overview

This Terraform module provisions a NAT instance in AWS to enable outbound internet access for private subnets. The module sets up an Amazon Linux EC2 instance with appropriate IAM roles, security groups, and routing configurations to function as a NAT instance.

Features

• Creates an EC2 NAT instance with Amazon Linux
• Configures security groups to allow necessary traffic
• Sets up IAM roles for instance management via AWS Systems Manager (SSM)
• Provisions a network interface with source/destination check disabled
• Configures route tables to direct private subnet traffic through the NAT instance

Usage

module "nat_instance" {
  source = "./modules/nat-instance"

  aws_vpc_id                            = "vpc-12345678"
  nat_instance_type                     = "t3.micro"
  number_of_azs                          = 2
  private_subnets_ids                    = ["subnet-abcdef12", "subnet-abcdef34"]
  public_subnets_ids                     = ["subnet-12345678", "subnet-87654321"]
  amazon_ec2_linux_image                 = "amzn2-ami-kernel-5.10-hvm-*"
  amazon_ec2_instance_virtualization_type = "hvm"
  amazon_owner_id                        = "137112412989"
  ssm_agent_policy                       = "arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore"
}

Inputs

Variable	Description	Type	Default
aws_vpc_id	The ID of the VPC where the NAT instance will be deployed	string	n/a
nat_instance_type	The EC2 instance type (e.g., t3.micro, t3.small)	string	n/a
number_of_azs	The number of availability zones to distribute the infrastructure across	number	n/a
private_subnets_ids	A list of private subnet IDs that require outbound internet access	list(string)	n/a
public_subnets_ids	A list of public subnet IDs where the NAT instance will be placed	list(string)	n/a
amazon_ec2_linux_image	Amazon Linux image for the NAT instance	string	amzn2-ami-kernel-5.10-hvm-*
amazon_ec2_instance_virtualization_type	Virtualization type for the EC2 instance	string	hvm
amazon_owner_id	AWS account ID of the AMI owner	string	137112412989
ssm_agent_policy	IAM policy ARN for SSM agent management	string	arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore

Outputs

Output	Description
nat_instance_id	The ID of the NAT EC2 instance
nat_instance_security_group_id	The security group ID assigned to the NAT instance
nat_instance_private_ip	The private IP address of the NAT instance
nat_instance_public_ip	The public IP address (if assigned)

Security

• The instance profile allows management via AWS Systems Manager (SSM) without requiring SSH access.
• Security groups restrict inbound traffic to the VPC’s CIDR block.

License

This module is licensed under the MIT License.

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🤝 Contributing

Contributions are welcome! Fork the repository and submit a pull request with bug fixes, improvements, or new features.

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