A company is building a serverless application to process ecommerce orders.

The key requirements are asynchronous processing, high availability, burst handling, and strict message ordering. Amazon SQS FIFO queues are specifically designed to guarantee exactly-once processing and ordered message delivery, making them ideal for transactional workflows like ecommerce order processing.

Option B meets all requirements. SQS FIFO preserves the order of messages within a message group and scales automatically to absorb traffic spikes. Integrating SQS FIFO with AWS Lambda enables serverless, event-driven processing with automatic scaling and no infrastructure management. Lambda processes messages as they arrive while maintaining order guarantees.

Option A (SNS) does not guarantee ordering and is designed for fan-out messaging. Option C (SQS standard) scales well but does not preserve order. Option D introduces unnecessary batch infrastructure and increased latency.

Therefore, B is the best solution because it combines ordered delivery, resilience, elasticity, and serverless compute, ensuring reliable and scalable order processing.