SAA-C03 Design Resilient Architectures Practice Question
An engineering team deploys a stateless web API on EC2 using an Auto Scaling group and an Application Load Balancer (ALB). During a recent test, they noticed that when one Availability Zone was unavailable, traffic failed until new instances were manually launched. Which change most directly improves automatic failover for the compute layer within a single Region?
⚠ Common exam trap
A common mix-up: candidates think a single-AZ setup with a load balancer is sufficient for high availability, but without multi-AZ subnets for both the ALB and Auto Scaling group, the architecture remains vulnerable to AZ failure and requires manual recovery.
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
✓
Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
Placing both the ALB and the Auto Scaling group across multiple subnets in at least two Availability Zones ensures that if one AZ becomes unavailable, the ALB can route traffic to healthy instances in the remaining AZs, and the Auto Scaling group can automatically launch replacement instances in the other AZs. This directly provides automatic failover for the compute layer within a single Region without manual intervention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place the Auto Scaling group in only one subnet so instance launches are simpler.
Why it's wrong here
Using only one subnet/AZ removes redundancy. An AZ outage would still take down capacity until manual action occurs.
- ✓
Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
Why this is correct
Spreading the ALB and Auto Scaling group across at least two AZs provides redundant capacity. If one AZ fails, the ALB continues routing to healthy targets in the other AZ.
- ✗
Increase the target group deregistration delay to allow old instances to stay longer.
Why it's wrong here
Changing deregistration delay affects connection draining, not capacity placement across AZs. It doesn’t create additional resilient instances.
- ✗
Use a Network Load Balancer, but keep all subnets in a single Availability Zone.
Why it's wrong here
Switching load balancer type doesn’t fix the root cause. If capacity is only in one AZ, failures will still impact the service.
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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.