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.
Exhibit
Current deployment:
Application Load Balancer subnets: subnet-a1 (AZ-a), subnet-a2 (AZ-a)
Auto Scaling group subnets: subnet-a1 (AZ-a) only
Desired capacity: 4 instances
Minimum capacity: 4 instances
Incident report:
2026-04-18T09:21Z AZ-a experienced a power issue
2026-04-18T09:22Z all targets became unhealthy
2026-04-18T09:25Z service returned HTTP 503 to users
Based on the exhibit, the application should continue serving requests if one Availability Zone fails. Which change best improves resilience with the least operational complexity?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Current deployment:
Application Load Balancer subnets: subnet-a1 (AZ-a), subnet-a2 (AZ-a)
Auto Scaling group subnets: subnet-a1 (AZ-a) only
Desired capacity: 4 instances
Minimum capacity: 4 instances
Incident report:
2026-04-18T09:21Z AZ-a experienced a power issue
2026-04-18T09:22Z all targets became unhealthy
2026-04-18T09:25Z service returned HTTP 503 to users
A
Increase the desired capacity in AZ-a so more instances can absorb the failure of that same Availability Zone.
Why wrong: Adding more instances in the same Availability Zone does not protect against an AZ-wide outage because all of those instances fail together.
B
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
A resilient design needs the load balancer and the Auto Scaling group to span multiple Availability Zones. If one AZ fails, the ALB can still route to healthy targets in the remaining AZs and the Auto Scaling group can replenish capacity there. This is the simplest and most common way to achieve AZ-level fault tolerance.
C
Disable health checks so the ALB stops removing targets during brief infrastructure issues.
Why wrong: Disabling health checks hides failures instead of recovering from them. The load balancer would continue sending traffic to unhealthy targets, which makes the outage worse rather than better.
D
Move the application to a single larger instance type so the fleet has fewer moving parts.
Why wrong: A single larger instance increases concentration risk and does not remove the Availability Zone single point of failure. It reduces the number of instances, but it also reduces redundancy.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
Option B is correct because adding subnets from a second Availability Zone to both the ALB and the Auto Scaling group distributes the application across multiple AZs. This ensures that if one AZ fails, the ALB can route traffic to healthy targets in the remaining AZ, and the Auto Scaling group can maintain capacity by launching instances in the surviving AZ. This approach directly addresses the requirement to continue serving requests during an AZ failure with minimal operational complexity.
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.
✗
Increase the desired capacity in AZ-a so more instances can absorb the failure of that same Availability Zone.
Why it's wrong here
Adding more instances in the same Availability Zone does not protect against an AZ-wide outage because all of those instances fail together.
✓
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
Why this is correct
A resilient design needs the load balancer and the Auto Scaling group to span multiple Availability Zones. If one AZ fails, the ALB can still route to healthy targets in the remaining AZs and the Auto Scaling group can replenish capacity there. This is the simplest and most common way to achieve AZ-level fault tolerance.
Clue confirmation
The clue words "best", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable health checks so the ALB stops removing targets during brief infrastructure issues.
Why it's wrong here
Disabling health checks hides failures instead of recovering from them. The load balancer would continue sending traffic to unhealthy targets, which makes the outage worse rather than better.
✗
Move the application to a single larger instance type so the fleet has fewer moving parts.
Why it's wrong here
A single larger instance increases concentration risk and does not remove the Availability Zone single point of failure. It reduces the number of instances, but it also reduces redundancy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think increasing capacity in a single AZ (Option A) provides resilience, but it actually concentrates risk in that AZ, while the correct answer requires distributing resources across multiple AZs to achieve true fault tolerance.
Detailed technical explanation
How to think about this question
Under the hood, an Application Load Balancer (ALB) is a regional service that can route traffic to targets in multiple AZs, but it must have at least one subnet in each AZ where targets reside to enable cross-zone load balancing. The Auto Scaling group uses the subnets specified in its launch configuration to launch instances; by adding subnets from a second AZ, the group can automatically replace failed instances in a different AZ, leveraging the ALB's health check mechanism (HTTP/HTTPS health checks on the configured path) to detect and reroute traffic away from unhealthy targets. In a real-world scenario, this design is critical for meeting SLAs that require 99.99% availability, as it withstands an entire AZ outage without manual intervention.
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: Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group. — Option B is correct because adding subnets from a second Availability Zone to both the ALB and the Auto Scaling group distributes the application across multiple AZs. This ensures that if one AZ fails, the ALB can route traffic to healthy targets in the remaining AZ, and the Auto Scaling group can maintain capacity by launching instances in the surviving AZ. This approach directly addresses the requirement to continue serving requests during an AZ failure with minimal operational complexity.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best", "least". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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