An application uses a filesystem API to read and write data. It runs on EC2 instances across multiple Availability Zones and all instances must share the same filesystem. Data is small today but is expected to grow to tens of terabytes over time. Which storage approach scales best for this requirement?

Amazon EFS (Elastic File System) is a fully managed, scalable, and highly available network file system designed for EC2 instances. It supports concurrent connections from multiple instances across multiple Availability Zones, making it ideal for shared file access. EFS automatically scales storage capacity up and down as needed, supporting petabytes of data, which aligns with the expected growth to tens of terabytes. Mounting EFS via mount targets in required subnets provides low-latency access. Attaching a single EBS volume to multiple instances is not supported for shared access (unless using Multi-Attach for specific use cases, which is not a general shared filesystem solution and doesn't scale to multiple AZs easily). Launching an EC2 instance to export a filesystem creates a single point of failure and requires manual management and scaling. AWS Storage Gateway cached volume appliance is primarily for hybrid cloud storage and is not the most direct or scalable solution for shared file access between EC2 instances within AWS.