Question: What's the best practice for horizontally scaling a legacy ASP.NET web application that relies on Active Directory and is currently deployed to a single Windows EC2 instance?

1. Use Sysprep to shut down the instance during a maintenance window. Create an AMI image and place both servers behind Application Load Balancer with sticky sessions.
2. Launch a new EC2 with the latest version of Windows Server and install the application again. Use Application Load Balancer and sticky sessions to balance between both servers.
3. Create a clone of the server using an AMI image and user Application Load Balancer to balance the traffic between both instances using sticky sessions.
4. Horizontal scaling is not the best practice in this situation. Increase the size of the existing EC2 instance and vertically scale the application.

Answer: The correct answer of the above question is Option A:Use Sysprep to shut down the instance during a maintenance window. Create an AMI image and place both servers behind Application Load Balancer with sticky sessions.