An e-commerce web application that shares session state on-premises is being migrated to AWS. The application must be fault tolerant, natively highly scalable, and any service interruption should not

ElastiCache (Redis or Memcached) is specifically designed for low-latency, high-throughput session data storage. Redis supports replication and automatic failover across Availability Zones, making it fault tolerant. It scales horizontally and is decoupled from the application tier, so any application instance can retrieve session data, enabling true horizontal scalability.

CloudFront is a content delivery network for caching static and dynamic content at edge locations; it is not designed to store mutable, user-specific session state.

Amazon S3 is object storage optimized for large, infrequently accessed objects; its eventual-consistency model and higher latency make it unsuitable for session state requiring millisecond read/write performance.

Session stickiness routes a user to the same instance, creating a single point of failure and preventing true horizontal scaling, which directly contradicts the fault-tolerant and scalable requirements.