Shared File Storage for Multi-AZ EC2 Instances

SAA-C03 By islever Editorial Last updated

Determine high-performing and/or scalable storage solutions.

Short answer

D Configure an Amazon Elastic File System (Amazon EFS) file system and mount it across all instances.

Question

A company is running a media store across multiple Amazon EC2 instances distributed across multiple Availability Zones in a single VPC. The company wants a high-performing solution to share data between all the EC2 instances, and prefers to keep the data within the VPC only. What should a solutions architect recommend?
  1. Create an Amazon S3 bucket and call the service APIs from each instance's application
  2. Create an Amazon S3 bucket and configure all instances to access it as a mounted volume
  3. Configure an Amazon Elastic Block Store (Amazon EBS) volume and mount it across all instances
  4. Configure an Amazon Elastic File System (Amazon EFS) file system and mount it across all instances Correct Answer

Key Takeaways

This question tests knowledge of shared storage options by contrasting EBS (single-instance) with EFS (multi-instance), highlighting the trap of choosing S3 when a POSIX-compliant file mount is required.

Amazon EFS is the recommended solution for sharing data across multiple EC2 instances in different Availability Zones while keeping data within the VPC. It provides a scalable, managed file system that supports concurrent access.

Common mistake: Candidates often choose Amazon S3 because it is durable and cheap, but fail to recognize that S3 uses object APIs rather than providing a mounted file system interface suitable for direct application file operations.

Expert Analysis

Why the Answer Is Correct

Amazon EFS is a fully managed elastic file system designed to work with Linux-based AWS and on-premises resources. It supports the Network File System (NFSv4.1) protocol, allowing it to be mounted concurrently on hundreds of EC2 instances simultaneously. Because EFS scales elastically and is built for high availability across multiple Availability Zones within a single VPC, it perfectly fits the requirement for a high-performing, shared data store accessible by all instances.

Why the Other Options Are Wrong

Option A and B involve Amazon S3, which is an object storage service. While S3 is highly durable and scalable, it does not present as a mounted file system volume; applications must use SDKs or REST APIs to interact with it, which is not equivalent to mounting a shared drive. Option C suggests using an Amazon EBS volume, but standard EBS volumes can only be attached to one EC2 instance at a time (unless using specific multi-attach features for IOPS SSDs, which still have limitations and do not support the same broad multi-AZ concurrency model as EFS). Therefore, EBS cannot serve as a shared filesystem for all instances.

Community Comment Notes

The community consensus strongly favors option D, noting that EFS is the only option that allows simultaneous mounting across multiple instances. As user Sarayounisaldossary noted, "EFS is a fully managed, shared file system... Perfect fit for the use case." Another user simply confirmed, "D is the right answer," reinforcing the standard architectural pattern for this scenario.

Official Reference

https://docs.aws.amazon.com/efs/latest/ug/whatisefs.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

Always distinguish between block storage (EBS), object storage (S3), and file storage (EFS) based on access patterns. If the requirement specifies 'mounting' across multiple instances, EFS is typically the correct choice over S3 or EBS.

Frequently Asked Questions

Can EBS volumes be shared across multiple EC2 instances?

Standard EBS volumes attach to one instance. Multi-Attach allows limited sharing on specific io1/io2 volumes, but EFS is the primary solution for general-purpose multi-instance file sharing.

Why not use S3 for sharing data between EC2 instances?

S3 is object storage accessed via API/SDK. It cannot be mounted as a native file system volume like EFS or EBS, making it unsuitable for applications requiring POSIX file semantics.

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Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. Sarayounisaldossary 👍 1 Answered D
    Why is EFS the correct answer? Amazon EFS is a fully managed, shared file system. It can be mounted on multiple EC2 instances at the same time. It works across multiple Availability Zones. High performance, and keeps all data within the VPC. Perfect fit for the use case: “Share data between EC2 instances.” Other options: S3 is object storage, not a shared file system. EBS can be attached to only one instance at a time. Mounting S3 isn’t officially supported or reliable.
  2. aragon_saa 👍 4 Answered D
    Answer is D
  3. muhammadahmer36 👍 3 Answered D
    D is the right answer

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