AWS Multi-Account Network Architecture with Infrastructure Account

Overview

This document outlines the design and implementation of a multi-account AWS network architecture using a dedicated Infrastructure Account for centralized network management. The solution leverages AWS Transit Gateway for inter-VPC connectivity and automates VPC creation across member accounts using CloudFormation Stack Sets.

Architecture Components

Account Structure

1. Management Account

   • Primary purpose: AWS Organizations management

   • Responsibilities:

     • Organization-wide governance

     • Account management

     • Service control policies (SCPs)

     • Billing and cost management

2. Infrastructure Account

   • Primary purpose: Centralized network management

   • Responsibilities:

     • Transit Gateway management

     • Network resource deployment automation

     • Network monitoring and operations

     • Network security controls

3. Member Accounts

   • Purpose: Workload hosting

   • Contain: Application-specific VPCs

   • Connect: Via Transit Gateway attachments

Implementation Guide

Phase 1: Account Setup

1. Infrastructure Account Creation

# Create dedicated Infrastructure Account through Organizations
aws organizations create-account \
    --email [e-mail] \
    --account-name "Network Infrastructure"

1. Required IAM Roles

# infrastructure-account-roles.yaml
Resources:
  NetworkAdminRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: cloudformation.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/AWSNetworkAdministrator

Phase 2: Transit Gateway Setup

1. Create Transit Gateway

# transit-gateway.yaml
Resources:
  CentralTransitGateway:
    Type: AWS::EC2::TransitGateway
    Properties:
      AmazonSideAsn: 64512
      AutoAcceptSharedAttachments: enable
      DefaultRouteTableAssociation: enable
      DefaultRouteTablePropagation: enable
      Description: Central Transit Gateway for Organization
      Tags:
        - Key: Environment
          Value: Production

1. Configure Resource Sharing

# resource-sharing.yaml
Resources:
  TransitGatewayShare:
    Type: AWS::RAM::ResourceShare
    Properties:
      Name: OrganizationTransitGatewayShare
      Principals: 
        - '*'
      ResourceArns:
        - !Ref CentralTransitGateway

Phase 3: Stack Set Configuration

1. Stack Set IAM Roles

# stackset-roles.yaml
Resources:
  StackSetAdminRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: cloudformation.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/AdministratorAccess

1. VPC Template

# member-vpc-template.yaml
Parameters:
  TransitGatewayId:
    Type: String
    Description: ID of the shared Transit Gateway

Resources:
  MemberVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Sub 10.${AWS::AccountId}.0.0/16
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
        - Key: Purpose
          Value: Workload

  TransitGatewayAttachment:
    Type: AWS::EC2::TransitGatewayAttachment
    Properties:
      TransitGatewayId: !Ref TransitGatewayId
      VpcId: !Ref MemberVPC
      SubnetIds: !Ref PrivateSubnets

Phase 4: Automation Implementation

1. Stack Set Deployment

# Deploy from Infrastructure Account
aws cloudformation create-stack-set \
    --stack-set-name member-vpc-deployment \
    --template-body file://member-vpc-template.yaml \
    --capabilities CAPABILITY_NAMED_IAM \
    --permission-model SERVICE_MANAGED

1. Stack Instance Creation

aws cloudformation create-stack-instances \
    --stack-set-name member-vpc-deployment \
    --regions us-east-1 \
    --deployment-targets OrganizationalUnitIds='["ou-xxxx-xxxxxxxx"]'

Network Operations

Monitoring Setup

1. VPC Flow Logs Configuration

2. Transit Gateway Network Manager

3. CloudWatch Metrics and Alarms

Security Controls

1. Network Access Controls

   • Security Groups

   • NACLs

   • Route Table management

2. Compliance Requirements

   • Traffic monitoring

   • Security assessments

   • Compliance reporting

Operational Procedures

1. New Account Onboarding

2. Route Management

3. Troubleshooting Process

Best Practices

Architecture Principles

1. Centralization

   • Single point of network control

   • Consistent policy enforcement

   • Unified monitoring

2. Automation

   • Infrastructure as Code

   • Automated deployments

   • Version control

3. Security

   • Least privilege access

   • Network segmentation

   • Continuous monitoring

Cost Management

1. Transit Gateway pricing considerations

2. VPC networking costs

3. Cross-AZ traffic optimization

Troubleshooting Guide

Common Issues

1. Stack Set Deployment Failures

   • Permission issues

   • Network constraints

   • Resource limits

2. Connectivity Problems

   • Route table configuration

   • Security group rules

   • Transit Gateway attachments

Resolution Steps

1. Verification Procedures

2. Logging Analysis

3. Escalation Process

Maintenance and Updates

Regular Tasks

1. Route table audits

2. Security group reviews

3. Compliance checking

Change Management

1. Network changes

2. Stack Set updates

3. Security patches

Appendix

Reference Architecture

[Include the architecture diagram]

Useful Commands

# Check Transit Gateway status
aws ec2 describe-transit-gateways

# List Stack Set operations
aws cloudformation list-stack-set-operations

# Verify route propagation
aws ec2 describe-transit-gateway-route-tables

Documentation Links

1. AWS Transit Gateway

2. AWS Organizations

3. CloudFormation Stack Sets

Version History

Version	Date	Author	Changes
1.0	2025-01-11	Network Team	Initial document

---

End of Document