A company uses AWS Organizations. The company runs two firewall appliances in a centralized networking account. Each firewall appliance runs on a manually configured highly available Amazon EC2 instance. A transit gateway connects the VPC from the centralized networking account to VPCs of member accounts. Each firewall appliance uses a static private IP address that is then used to route traffic from the member accounts to the internet. During a recent incident, a badly configured script initiated the termination of both firewall appliances. During the rebuild of the firewall appliances, the company wrote a new script to configure the firewall appliances at startup. The company wants to modernize the deployment of the firewall appliances. The firewall appliances need the ability to scale horizontally to handle increased traffic when the network expands. The company must continue to use the firewall appliances to comply with company policy. The provider of the firewall appliances has confirmed that the latest version of the firewall code will work with all AWS services. Which combination of steps should the solutions architect recommend to meet these requirements MOST cost-effectively? (Choose three.)