The existing architecture has two important bottlenecks: a single ECS compute node and files stored on storage attached to that individual ECS instance. Option E eliminates the compute single point of failure. A custom image allows identical ECS instances to be created, while Auto Scaling maintains multiple instances and ALB distributes requests across healthy backends. This provides horizontal scalability and significantly stronger application availability.

Option D addresses shared application storage. File Storage NAS is a managed, POSIX-compatible shared filesystem that multiple ECS instances can mount concurrently. All web servers therefore see the same files, while NAS handles storage scalability and consistency independently from the ECS lifecycle.

Option A improves performance by moving cacheable website content toward users. CDN serves static resources from nearby POPs and reduces requests and bandwidth reaching the origin infrastructure.

Although OSS is excellent for native object-storage workloads, mounting OSS through ossfs does not provide the same filesystem semantics and consistency characteristics as NAS for a traditional application requiring minimal modification. Global Accelerator primarily optimizes network paths and does not eliminate the application ' s compute or storage single points of failure.

Study Guide reference: Building Highly Available, Performant Cloud Architecture — ALB, Auto Scaling, NAS shared storage, and CDN.

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