Answer: Create an Amazon Elastic File System (Amazon EFS) file system. Mount the EFS file system on all web servers.

## Explanation **Correct Answer: C** - Create an Amazon Elastic File System (Amazon EFS) file system and mount it on all web servers. **Why this is correct:** 1. **Shared File System Requirement**: The scenario requires a "shared file store" that multiple web servers can access simultaneously. Amazon EFS is specifically designed as a fully managed, scalable, shared file system for Linux-based applications. 2. **No Application Changes**: The requirement states "must not make any changes to the application." EFS provides a standard NFSv4 interface that can be mounted on Linux instances, allowing applications to access files using standard file system operations without code modifications. 3. **Multi-Server Access**: EFS supports concurrent access from multiple EC2 instances, making it ideal for web server clusters that need to share content. **Why other options are incorrect:** - **A (Amazon S3)**: S3 is an object storage service, not a file system. While it can store files, it requires application changes to use S3 APIs instead of standard file system operations. - **B (CloudFront with S3)**: This is for content delivery and caching, not for providing a shared file store that web servers can directly access for reading/writing files. - **D (EBS volume)**: EBS volumes can only be attached to a single EC2 instance at a time. They cannot be simultaneously mounted to multiple web servers, which violates the shared access requirement. **Key AWS Services Comparison:** - **EFS**: Shared file system for Linux, NFS protocol, multi-attach support - **EBS**: Block storage, single-attach only (except for specific multi-attach volumes with limitations) - **S3**: Object storage, requires API access - **CloudFront**: CDN for content delivery This solution meets all requirements: shared file access, no application changes, and Linux compatibility.

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