SAA-C03 Design Resilient Architectures Practice Question
A patient portal must use shared file storage across Linux EC2 instances in multiple Availability Zones. The storage must remain available during an AZ failure. Which service should be used? The design must avoid adding custom operational scripts.
⚠ Common exam trap
Watch out — candidates often confuse EBS multi-attach (which is limited to specific instance types and a single AZ) with a true cross-AZ shared file system, or assume S3 with a FUSE mount provides POSIX compliance without operational overhead.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Amazon EFS with mount targets in multiple Availability Zones
Amazon EFS provides a fully managed, scalable, and shared file system that can be mounted concurrently on multiple Linux EC2 instances across different Availability Zones. By creating mount targets in each AZ, the file system remains accessible even if one AZ fails, meeting the high availability requirement without custom scripts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Instance store volumes
Why it's wrong here
Instance store volumes are physically attached to a single EC2 host and have a lifespan tied to that instance; data is lost when the instance is stopped or terminated. They are local to one instance only, so other EC2 instances in different Availability Zones cannot access the same data. This ephemeral, single-instance nature makes it impossible to use instance store as shared file storage for a multi-instance patient portal.
- ✓
Amazon EFS with mount targets in multiple Availability Zones
Why this is correct
Amazon EFS is a fully managed, regional NFS-based file system that supports the POSIX standard, making it ideal for Linux workloads. By creating mount targets in multiple Availability Zones, all EC2 instances can concurrently read and write the same files with low latency and high availability. EFS automatically scales capacity and is designed to be accessed by thousands of instances simultaneously, satisfying the shared file storage requirement across AZs.
- ✗
An EBS volume attached to all instances
Why it's wrong here
A standard EBS volume is a block-level storage device that can be attached to only one EC2 instance at a time, and it is zonal—confined to a single Availability Zone. While multi-attach EBS is available for specific io1/io2 volumes, it only works within the same AZ and requires a clustered file system, making it impractical for broad multi-AZ sharing. Attaching one EBS volume to all instances is not supported and would not provide the shared file storage the portal needs.
- ✗
S3 mounted as a POSIX file system without a file gateway
Why it's wrong here
S3 is an object storage service, not a file system, and it does not natively provide POSIX semantics such as file locking, in-place directory operations, or strong consistency for all operations. Tools like s3fs can mount S3 as a POSIX-like filesystem, but they rely on workarounds that introduce performance and consistency issues, and they require a gateway or third-party software. Without Amazon File Gateway, directly mounting S3 as a POSIX file system is not a reliable solution for shared file storage for multiple Linux EC2 instances.
Go deeper
Related to this question
About these practice questions
One of 935 original SAA-C03 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.