A company runs an ecommerce website on AWS.

The correct answer is B because the company explicitly wants to move from a monolithic architecture to a loosely coupled architecture that supports independent scaling . Refactoring the application into microservices is the architectural approach that best meets that requirement. Running the microservices on Amazon ECS containers provides a managed container orchestration platform with less operational overhead than managing a Kubernetes environment.

With microservices, separate business functions such as product catalog management and customer checkout can be deployed as individual services. Each service can scale independently based on its own traffic and performance characteristics. This is far more efficient than scaling the entire monolithic application when only one part of the system experiences increased demand.

An Application Load Balancer is appropriate because it can route HTTP and HTTPS traffic and supports path-based and host-based routing, which is useful for directing requests to different services. This design improves agility, performance, and operational flexibility while supporting the company’s need for growth.

Option A improves availability and scalability, but it still runs a copy of the same monolithic application on multiple EC2 instances. That does not enable independent scaling of individual functions. Option C creates a basic two-tier design, but it is not a fully loosely coupled microservices architecture. Option D uses Amazon EKS but places the application into a single container , which does not achieve independent scaling of separate components and introduces more operational complexity than necessary.

AWS architectural best practices recommend decomposing monoliths into microservices when independent scaling, agility, and component isolation are required. Therefore, Amazon ECS with microservices is the best solution.