SAA-C03 Design Resilient Architectures Practice Question
Your ecommerce app runs behind an Application Load Balancer (ALB) and uses an RDS database for orders. During an AZ impairment in us-east-1, customers report that checkout takes several minutes to recover. The current design places EC2 instances only in private subnets of AZ-a, while the ALB spans multiple subnets. The RDS DB instance is Multi-AZ. Management wants automatic recovery within the same Region.
Which change best addresses the issue with minimal operational overhead?
⚠ Common exam trap
The trap here is that candidates may focus on the database layer (Multi-AZ) or load balancer type (NLB vs ALB) and overlook the critical single-AZ EC2 instance placement, which is the actual bottleneck causing the prolonged recovery during an AZ impairment.
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
✓
Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
The current design has a single point of failure: all EC2 instances are in one Availability Zone (AZ-a). During an AZ impairment, those instances become unreachable, causing the checkout process to fail until the impairment ends or manual intervention occurs. By placing EC2 instances in an Auto Scaling Group spanning at least two AZs, the application can automatically recover by launching new instances in a healthy AZ, while the ALB distributes traffic across the surviving AZs. This minimizes operational overhead as Auto Scaling handles instance replacement automatically.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
Why this is correct
An Auto Scaling Group across multiple AZs ensures healthy capacity exists when an AZ becomes impaired, and the ALB can route to instances in any available AZ.
- ✗
Switch from RDS Single-AZ to RDS Multi-AZ, keeping the EC2 instances in only AZ-a because failover will still reach them.
Why it's wrong here
RDS failover helps database availability, but the observed checkout delay stems from lack of compute capacity in the impaired AZ.
- ✗
Terminate the ALB and use a Network Load Balancer (NLB) in front of the existing single-AZ EC2 instances.
Why it's wrong here
Changing load balancer type does not fix the dependency on instances only in AZ-a, so recovery will still be impacted.
- ✗
Add more EC2 instances in AZ-a and increase the ALB health check thresholds to avoid unnecessary replacements during impairments.
Why it's wrong here
Overprovisioning in a single AZ reduces but does not eliminate unavailability when that AZ is degraded and cannot serve traffic.
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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.