SOA-C02 Reliability and Business Continuity Practice Question
An application running on Amazon ECS with Fargate launch type is experiencing intermittent failures. The tasks are spread across multiple Availability Zones. The SysOps administrator notices that failures occur only when an entire AZ becomes unavailable. What should the administrator do to improve the reliability of the application?
⚠ Common exam trap
It's easy for candidates to think adding storage (EFS) or using placement groups (which are EC2-specific) can solve AZ-level failures, but the core issue is ensuring enough task capacity across multiple AZs to survive the loss of one.
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
✓
Increase the desired task count to ensure sufficient capacity across AZs.
Increasing the desired task count ensures that ECS Fargate tasks are distributed across multiple Availability Zones, providing sufficient capacity to absorb the loss of an entire AZ. When one AZ becomes unavailable, the remaining tasks in other AZs continue to serve traffic, improving application reliability. This approach leverages the multi-AZ architecture already in place by ensuring enough tasks are running to handle the load even after an AZ failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use multiple subnets in the same AZ.
Why it's wrong here
Creating multiple subnets within the same Availability Zone does not increase redundancy because the AZ itself is the failure domain. If that AZ becomes unavailable or experiences network degradation, every subnet contained within it is affected simultaneously. For ECS Fargate tasks to remain highly available, you must place them across subnets that belong to different AZs.
- ✗
Use a cluster placement group.
Why it's wrong here
Placement groups are an Amazon EC2 feature that control how instances are placed on underlying hardware; they do not apply to Fargate tasks because Fargate is a serverless compute engine where you do not provision or manage instances. Moreover, placement groups are designed for low latency or high availability of EC2 instances, not for distributing Fargate tasks across AZs. This option is therefore irrelevant to achieving AZ-level fault tolerance.
- ✗
Attach an Amazon EFS filesystem to all tasks.
Why it's wrong here
An Amazon EFS file system provides shared, persistent storage accessible across multiple tasks and Availability Zones, but it does not provide compute or runtime redundancy. If the application tasks fail or the AZ hosting them fails, having a shared file system does nothing to keep the application running or to reroute traffic. You still need a sufficient number of Fargate tasks deployed across AZs.
- ✓
Increase the desired task count to ensure sufficient capacity across AZs.
Why this is correct
Increasing the desired task count for an ECS service ensures that more Fargate tasks are running, and because the service scheduler distributes tasks across the AZs represented in your VPC subnets, this gives you capacity to absorb an AZ failure. With a higher replica count, if one AZ fails, the remaining tasks in other AZs can continue servicing traffic, and the service can eventually replace tasks in healthy AZs. This is the correct way to provide compute redundancy for a Fargate-based application.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 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 SOA-C02 exam.