The current architecture tightly couples image upload, resizing, and storage into a single synchronous workflow handled by EC2 instances. This increases upload latency and degrades user experience. The optimal solution is to decouple upload from processing and offload work to managed services.

Option C allows users’ browsers to upload images directly to Amazon S3 using presigned URLs, bypassing the EC2 web servers entirely. This significantly reduces server load, network hops, and request latency while improving scalability and performance. Presigned URLs also maintain security by granting time-limited, scoped access to S3.

Option D complements this by using S3 Event Notifications to invoke an AWS Lambda function whenever a new image is uploaded. The Lambda function performs the image resizing asynchronously and stores the processed image back in S3. This event-driven, serverless pattern eliminates tight coupling between upload and processing and ensures automatic scaling with minimal operational overhead.

Option A is unsuitable because Glacier is for archival storage and not designed for active uploads or processing. Option B still routes uploads through EC2, maintaining the bottleneck. Option E introduces unnecessary delays and inefficiency by resizing images on a schedule instead of reacting to upload events.

Therefore, C and D together provide the most performant, scalable, and operationally efficient image upload and processing architecture using AWS-native, event-driven services.