An application running on Amazon EC2 sometimes experiences sudden spikes in traffic. The company wants the application to scale automatically in response to demand while minimizing cost. Which AWS service or concept should they use?

AWS Auto Scaling is the correct choice because it dynamically adjusts the number of EC2 instances based on demand, ensuring performance during traffic spikes and scaling down during lulls to minimize costs. It directly addresses both the automatic scaling and cost optimization requirements. AWS Compute Optimizer provides recommendations for optimizing resource configurations, but it doesn't automatically scale resources. AWS Cost Explorer is a cost management tool for analyzing spending, not for operational scaling. The AWS Well-Architected Framework is a set of best practices for designing and operating reliable, secure, efficient, and cost-effective cloud systems, but it's a framework, not a service that performs automatic scaling.