AWS Fargate should be used to optimize the cost of a containerized application by eliminating the need for manual instance management, as it provides serverless container orchestration that automatically scales and charges only for resource usage. The WGU Cloud Deployment and Operations Study Guide (Section 7.5, Fargate) states, "Fargate optimizes costs for containerized applications by removing the overhead of managing EC2 instances, scaling automatically, and billing based on vCPU and memory usage, reducing manual deployment expenses." Aurora, RDS, and EFS are database or storage solutions not designed for container cost optimization.