Building an Enterprise-Grade AWS Landing Zone with Terraform

Creating a secure, scalable, and efficient cloud environment is crucial for businesses to innovate and grow. AWS offers a robust platform for deploying cloud resources, but managing these resources can become complex as your infrastructure grows. This comprehensive guide will explore how to build a secure AWS Landing Zone using Terraform, covering key components such as multi-account structure, AWS Organizations, Control Tower integration, network architecture, IAM policies, logging/monitoring, and security best practices.

A landing zone is the foundation of your AWS environment, providing a well-architected framework to manage your cloud resources securely and efficiently. By leveraging Terraform, an open-source Infrastructure as Code (IaC) tool, you can automate the deployment of your AWS landing zone, ensuring consistency and reducing the potential for human error.

Before diving into the specifics, let's define a few key concepts:

- **AWS Landing Zone**: A solution that helps customers more quickly set up a secure, multi-account AWS environment based on AWS best practices. - **Terraform**: An open-source tool created by HashiCorp, used for building, changing, and versioning infrastructure safely and efficiently. - **AWS Organizations**: A service for grouping and centrally managing multiple AWS accounts. - **AWS Control Tower**: A service that automates the setup of a well-architected multi-account AWS environment.

A multi-account AWS environment is beneficial for separating concerns, limiting the blast radius of incidents, and isolating environments (e.g., development, staging, production). AWS Organizations enables the creation and management of these accounts in a hierarchical, efficient manner.

resource "aws_organizations_organization" "my_org" {
  feature_set = "ALL"
}

resource "aws_organizations_account" "dev_account" {
  name      = "dev"
  email     = "dev@example.com"
  parent_id = aws_organizations_organization.my_org.roots[0].id
}

resource "aws_organizations_account" "prod_account" {
  name      = "prod"
  email     = "prod@example.com"
  parent_id = aws_organizations_organization.my_org.roots[0].id
}

This Terraform code snippet creates an AWS Organization with two accounts: one for development and another for production.

AWS Control Tower offers a way to automate the setup of a secure AWS Landing Zone. Integrating Control Tower with Terraform allows for the provisioning of Control Tower resources through code.

Currently, AWS Control Tower is not directly supported by Terraform in terms of a specific provider. However, you can use a combination of AWS Organizations, SSO, and other services to mimic the functionality of Control Tower. Keep an eye on Terraform updates for future support.

A well-designed network is critical for security, performance, and scalability. AWS Virtual Private Cloud (VPC) and AWS Transit Gateway are central components of a robust network architecture.

resource "aws_vpc" "main_vpc" {
  cidr_block = "10.0.0.0/16"
  enable_dns_support = true
  enable_dns_hostnames = true
  tags = {
    Name = "main_vpc"
  }
}

This code creates a VPC with DNS support and hostnames enabled, tagged as `main_vpc`.

resource "aws_ec2_transit_gateway" "tgw" {
  description = "My Transit Gateway"
  tags = {
    Name = "my_tgw"
  }
}

The Transit Gateway serves as a hub that controls how traffic is routed among all the connected networks which can include VPCs, VPN connections, and more.

Identity and Access Management (IAM) policies are crucial for securing access to AWS resources. The principle of least privilege should always be followed, ensuring that identities have only the permissions necessary to perform their tasks.

resource "aws_iam_policy" "example_policy" {
  name        = "example_policy"
  description = "A test policy"
  policy      = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "ec2:Describe*"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}
EOF
}

This policy allows the action `ec2:Describe*` on all resources, which can be useful for read-only roles that need to view EC2 instances.

Centralized logging and monitoring are vital for maintaining the operational health and security of your AWS environment. AWS CloudWatch and AWS CloudTrail are essential services for accomplishing this.

resource "aws_cloudwatch_log_group" "my_log_group" {
  name = "/aws/lambda/my_lambda_function"
  retention_in_days = 14
}

resource "aws_cloudwatch_log_stream" "my_log_stream" {
  name           = "my_log_stream"
  log_group_name = aws_cloudwatch_log_group.my_log_group.name
}

This code sets up a CloudWatch Log Group for a Lambda function, with logs retained for 14 days.

resource "aws_cloudtrail" "my_cloudtrail" {
  name                          = "my_cloudtrail"
  s3_bucket_name                = aws_s3_bucket.my_bucket.bucket
  include_global_service_events = true
  is_multi_region_trail         = true
}

resource "aws_s3_bucket" "my_bucket" {
  bucket = "my-cloudtrail-logs"
  acl    = "private"
}

This snippet configures CloudTrail to log events, storing the logs in a specified S3 bucket.

Ensuring your AWS environment is secure involves adhering to best practices such as encrypting data at rest and in transit, using security groups and network ACLs effectively, and regularly auditing your environment.

resource "aws_s3_bucket" "secure_bucket" {
  bucket = "my-secure-bucket"
  acl    = "private"

  server_side_encryption_configuration {
    rule {
      apply_server_side_encryption_by_default {
        sse_algorithm = "AES256"
      }
    }
  }
}

This configuration ensures that data stored in the `my-secure-bucket` S3 bucket is encrypted using the AES256 algorithm.

Building a secure AWS landing zone is a comprehensive process that involves setting up a multi-account structure, designing a robust network architecture, implementing strict IAM policies, and ensuring that logging and monitoring are in place. By using Terraform to automate the deployment of these components, you can create a scalable, secure environment that aligns with AWS best practices. Remember to review and update your Terraform configurations and AWS resources regularly to keep up with evolving security threats and AWS features.