SAA-C03 Design Resilient Architectures Practice Question
This SAA-C03 practice question tests your understanding of design resilient architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A ticket booking system runs on EC2 instances behind an Application Load Balancer. The design must tolerate the failure of one Availability Zone. What should the Auto Scaling group configuration include?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Subnets in at least two Availability Zones with health checks enabled
Option A is correct because an Auto Scaling group configured with subnets in at least two Availability Zones and health checks enabled ensures that if one AZ fails, EC2 instances in the remaining AZs continue to serve traffic. The Application Load Balancer distributes requests across healthy instances in multiple AZs, and the Auto Scaling group replaces failed instances in the affected AZ, maintaining capacity. This design meets the requirement to tolerate the failure of one Availability Zone.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Subnets in at least two Availability Zones with health checks enabled
Why this is correct
An Auto Scaling group spanning multiple AZs can replace unhealthy instances and maintain capacity during an AZ failure.
Related concept
Read the scenario before looking for a memorised answer.
✗
All instances in one larger subnet
Why it's wrong here
One AZ remains a single point of failure.
✗
A Network Load Balancer in one subnet
Why it's wrong here
A load balancer in one AZ does not make the application resilient to AZ failure.
✗
A single EC2 instance with detailed monitoring
Why it's wrong here
Monitoring does not provide redundancy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think a single larger subnet or a different load balancer type provides resilience, but only distributing subnets across multiple Availability Zones with health checks ensures the system can survive an AZ failure.
Detailed technical explanation
How to think about this question
Under the hood, the Auto Scaling group uses the health check grace period (default 300 seconds) to allow new instances to stabilize before being marked healthy. The ALB performs health checks at the target group level (e.g., HTTP 200 on /health), and the Auto Scaling group integrates with these checks to replace unhealthy instances. In a real-world scenario, if an AZ experiences a power outage, the ALB stops routing traffic to instances in that AZ, and the Auto Scaling group launches replacement instances in the remaining AZs, but only if the group's subnets span multiple AZs.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design Resilient Architectures — This question tests Design Resilient Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Subnets in at least two Availability Zones with health checks enabled — Option A is correct because an Auto Scaling group configured with subnets in at least two Availability Zones and health checks enabled ensures that if one AZ fails, EC2 instances in the remaining AZs continue to serve traffic. The Application Load Balancer distributes requests across healthy instances in multiple AZs, and the Auto Scaling group replaces failed instances in the affected AZ, maintaining capacity. This design meets the requirement to tolerate the failure of one Availability Zone.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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