A company will run web servers on Amazon EC2 to serve customers worldwide. Most users access the site only during specific hours of the day. To minimize ongoing operational cost, how should the EC2 instances be deployed?

Placing instances in an Auto Scaling group that scales with demand is the most cost-effective solution. Auto Scaling automatically adjusts the number of EC2 instances based on demand, ensuring that you only pay for the resources you need when you need them. Since users access the site only during specific hours, scaling down during off-peak times significantly reduces operational costs. Deploying instances in multiple Availability Zones improves fault tolerance and high availability, but doesn't directly minimize ongoing operational cost. Launching instances in a placement group optimizes network performance between instances, which is not the primary concern for cost minimization here. Putting instances in private subnets enhances security by isolating them from the internet, but also doesn't address cost optimization based on fluctuating demand.