Amazon Elastic File System (EFS) is the ideal solution for this scenario. It provides a fully managed, scalable, and high-performance Network File System (NFS) that can be concurrently mounted by thousands of Amazon EC2 instances. EFS is a regional service, meaning it stores data across multiple Availability Zones (AZs) for high availability. By creating EFS mount targets in the subnets of each AZ where the EC2 instances are running, all instances can share the same file system seamlessly. All data traffic between the EC2 instances and the EFS file system remains within the Virtual Private Cloud (VPC), satisfying the security requirement.

A. Amazon S3 is an object storage service, not a file system. Accessing data via API calls is fundamentally different from a mounted file system and may not be suitable or performant for applications expecting POSIX-compliant file access.

B. Amazon S3 cannot be natively mounted as a volume on EC2 instances. This would require a third-party utility or a service like AWS Storage Gateway, which adds unnecessary complexity for this use case.

C. An Amazon EBS volume is block-level storage that is zonal; it can only be attached to instances within the same single Availability Zone. It cannot be mounted across instances in multiple AZs.

1. Amazon EFS User Guide

"What is Amazon EFS?": This document states

"Amazon EFS is a regional service

storing data within and across multiple Availability Zones (AZs) for high availability and durability... It provides massively parallel shared access to thousands of Amazon EC2 instances." This directly supports the use of EFS for shared access across multiple AZs.

2. Amazon EC2 User Guide for Linux Instances

"Amazon EBS volumes": This guide clarifies the limitation of EBS

stating

"EBS volumes are specific to an Availability Zone and can only be attached to instances in that same Availability Zone." This confirms why option C is incorrect.

3. Amazon EFS User Guide

"Mounting EFS file systems": This section explains how EFS works within a VPC: "You access your Amazon EFS file system from your VPC by connecting to a mount target... Traffic from your EC2 instance to the mount target is routed according to the VPC routing rules

" which ensures data stays within the VPC.

4. Amazon S3 User Guide

"What is Amazon S3?": This document defines S3 as "an object storage service" and notes that data is accessed via "the Amazon S3 REST API." This highlights the difference between S3's object-based access and the file-system access required by the scenario

making options A and B less suitable.