A company is migrating a data center to AWS. Several legacy applications run on individual virtual servers and cannot be redesigned. Each virtual server currently runs as its own EC2 instance. A solutions architect must ensure the applications are reliable and fault tolerant after migration. The applications will run on Amazon EC2 instances. Which solution meets these requirements?

The correct solution ensures reliability and fault tolerance for single-instance legacy applications. An Auto Scaling group with minimum and maximum instances set to one will automatically replace the EC2 instance if it becomes unhealthy, ensuring high availability. Creating an AMI of each application instance allows for consistent deployment. Placing an Application Load Balancer (ALB) in front provides a stable endpoint and can distribute traffic if the architecture evolves. The option to use AWS Backup provides disaster recovery but not immediate fault tolerance for an active instance failure. The option to launch two EC2 instances with a Network Load Balancer (NLB) would work for fault tolerance if the application could handle multiple active instances, but the question states "individual virtual servers" and "cannot be redesigned," implying a single active instance. AWS Mitigation Hub Refactor Spaces and Amazon ECS with Fargate involve redesigning the application, which is explicitly ruled out.