Which AWS best practice ensures the MOST cost-effective architecture for the workload?

Explanations:

Loose coupling refers to designing systems so that their components are independent. While it improves flexibility, it does not specifically address cost-effectiveness.

Rightsizing involves optimizing resources based on the actual usage and requirements of the workload, ensuring that costs are minimized while still meeting performance needs.

Caching can improve performance and reduce costs by minimizing the need for repeated data retrieval. However, it is not the primary practice for overall cost-effectiveness in architecture.

Redundancy is aimed at increasing availability and reliability of services, which can lead to higher costs due to the duplication of resources. It does not directly ensure cost-effectiveness.