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?
⚠ Common exam trap
It's easy for candidates to confuse EBS multi-attach (which is limited to specific instance types and does not span AZs) with the true multi-AZ shared file system capability of EFS.
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 scalable, fully managed NFS file system that can be mounted concurrently on multiple Linux EC2 instances. By creating mount targets in multiple Availability Zones, the file system remains accessible even if one AZ fails, ensuring high availability and shared file storage across instances.
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 provide temporary block-level storage physically attached to the host computer for the EC2 instance. They are ephemeral, meaning data is lost when the instance is stopped, terminated, or fails, and they cannot be shared across multiple instances because each instance has its own dedicated instance store. As a result, they cannot serve as durable, shared file storage for a patient portal spanning multiple Linux EC2 instances.
- ✓
Amazon EFS with mount targets in multiple Availability Zones
Why this is correct
Amazon EFS is a fully managed, regional file storage service that provides a POSIX-compliant NFS file system automatically scaled to meet demand. By creating mount targets in multiple Availability Zones, you enable Linux EC2 instances in those AZs to access the same shared file data simultaneously, with high availability and low latency. This makes EFS the appropriate choice for shared file storage for a patient portal across multiple Linux EC2 instances.
- ✗
An EBS volume attached to all instances
Why it's wrong here
A standard Amazon EBS volume is a block-level storage device that is created in a single Availability Zone and can be attached to only one EC2 instance at a time (unless you use the special Multi-Attach feature on certain volume types, which is limited to a few instances in the same AZ and still does not provide a true file-sharing model). Trying to attach an EBS volume to all instances is neither possible nor appropriate for shared file storage, and it would lack the distributed file system semantics needed by multiple Linux EC2 instances.
- ✗
S3 mounted as a POSIX file system without a file gateway
Why it's wrong here
Amazon S3 is an object storage service, not a POSIX-compliant file system; while you can use tools like s3fs to mount an S3 bucket as a file system, this approach lacks native file locking, consistent directory semantics, and adequate performance for concurrent writes, and it is generally not recommended for production workloads. Without AWS Storage Gateway's File Gateway (which presents a file-based NFS/SMB interface over S3), S3 does not provide the shared file system behavior required for a patient portal.
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Written by Johnson Ajibi, MSc IT Security
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