Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Site Reliability Engineer (SRE).
For SOA-C02 candidates, the confusion often lies in how Amazon EFS mount targets work across multiple Availability Zones to achieve low-latency file access. In production, this is about knowing exactly how to architect Amazon EFS for high availability and optimal performance across AZs by leveraging mount targets properly. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
A global media company, AlphaStream Technologies, employs a fleet of Amazon EC2 instances deployed across multiple Availability Zones within the same VPC to run their video transcoding workloads. For shared storage, the Site Reliability team wants to implement an Amazon Elastic File System (EFS) that all instances can mount. Each Availability Zone hosts two EC2 instances. The priority is to ensure the file system is accessible to every instance with the lowest possible latency.
The Requirement: #
Design a configuration for Amazon EFS mount targets that meets the low-latency and multi-AZ shared access requirements.
The Options #
- A) Create a single mount target for the EFS file system within the VPC and mount the file system via this target on all instances.
- B) Create a mount target in only one Availability Zone and have instances in all zones mount the file system through that single mount target.
- C) Create a mount target for each individual instance, and configure mounting through those specific targets.
- D) Create one mount target per Availability Zone in the VPC, then mount the file system on each instance using the mount target in their respective AZ.
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Correct Answer #
D.
Quick Insight: The SOA (SysOps) Imperative #
- Proper Amazon EFS deployment requires a mount target per Availability Zone for low latency and high availability.
- Mount targets are created at the subnet level per AZ, not per instance.
- Using a mount target in the same AZ minimizes latency and cross-AZ data traffic.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option D
The Winning Logic #
Amazon EFS uses mount targets to provide an entry point for network file systems within each Availability Zone of a VPC. For EC2 instances in multiple AZs, creating a mount target in each AZ allows the EC2 instances to mount the EFS file system locally within their own AZ subnet. This minimizes cross-AZ network latency and provides high availability in the event of AZ failure.
- Mount targets are created at the subnet level, not per instance, so Option C is invalid and impractical.
- Using only one mount target (Options A and B) forces all instances to traverse cross-AZ traffic for EFS access, increasing latency and potential bottlenecks.
- Distributing mount targets per AZ aligns with AWS best practice for latency-sensitive workloads that share EFS.
The Trap (Distractor Analysis): #
- Why not A? Single mount target for entire VPC does not exist; you must create mount targets per AZ.
- Why not B? Mount target only in one AZ causes increased cross-AZ latency and potential single point of failure.
- Why not C? Mount targets per instance are not supported and unnecessarily complex.
The Technical Blueprint #
# AWS CLI example to create mount targets in each Availability Zone's subnet
aws efs create-mount-target \
--file-system-id fs-12345678 \
--subnet-id subnet-aaa111 \
--security-groups sg-0123456789abcdef0
aws efs create-mount-target \
--file-system-id fs-12345678 \
--subnet-id subnet-bbb222 \
--security-groups sg-0123456789abcdef0
# Repeat for each AZ's subnet...
The Comparative Analysis #
| Option | Operational Overhead | Automation Level | Impact on Latency and Availability |
|---|---|---|---|
| A | Low (only one mount target) | Simple | High latency for instances in other AZs; single point of failure |
| B | Low | Simple | Increased cross-AZ data traffic, latency, risk |
| C | Very high | Complex, unsupported | Not supported, incorrect architecture |
| D | Moderate (multiple mount targets) | Requires some scripting/automation | Optimal latency per AZ, high availability |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the SOA-C02 exam, always remember: When designing Amazon EFS for multi-AZ EC2 workloads, a mount target must exist in each Availability Zone where instances reside.
Real World #
In production, not only latency but also fault tolerance drives this architecture. If one AZ’s mount target is down, others continue functioning independently.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS SOA-C02 exam.