- A
Reduce health check timeouts so instances are replaced sooner in the failed AZ.
Why wrong: Health check tuning can change how quickly instances are marked unhealthy and replaced, but it does not increase usable capacity in the remaining AZ. If the remaining AZ cannot sustain load, outages can still occur.
- B
Add a third Availability Zone so the ALB and Auto Scaling group span at least three AZs.
An AZ failure typically reduces available capacity to the other AZs. Spreading the ALB subnets and ASG instances across at least three AZs reduces the impact of losing any single AZ and helps ensure the remaining AZs can continue serving traffic.
- C
Enable instance scale-in protection to stop the ASG from terminating unhealthy instances.
Why wrong: Scale-in protection primarily affects scale-in actions (for example, terminating instances due to decreasing desired capacity). It does not solve the capacity-loss problem during an AZ failure, and it can interfere with replacing instances based on unhealthy status and replacement policies.
- D
Switch the ALB to an internal Network Load Balancer (NLB) to avoid cross-AZ traffic.
Why wrong: Changing from ALB to NLB does not provide additional AZ fault tolerance for the compute capacity placement. Cross-AZ traffic considerations are separate from handling an AZ outage.
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.
Your web tier runs on an EC2 Auto Scaling group behind an Application Load Balancer (ALB). You currently deploy both the ALB and the Auto Scaling group in only two Availability Zones (AZs). One AZ fails. What is the best configuration change to improve resilience?
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.
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
Add a third Availability Zone so the ALB and Auto Scaling group span at least three AZs.
Adding a third Availability Zone (AZ) ensures that the Application Load Balancer (ALB) and Auto Scaling group (ASG) can continue to route traffic and maintain capacity even if one AZ fails. With only two AZs, a single AZ failure reduces the fleet by 50% and may cause the ALB to lose the minimum healthy hosts required to serve traffic. Spreading across three AZs provides a higher resilience margin, as the remaining two AZs can absorb the load while the failed AZ recovers.
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.
- ✗
Reduce health check timeouts so instances are replaced sooner in the failed AZ.
Why it's wrong here
Health check tuning can change how quickly instances are marked unhealthy and replaced, but it does not increase usable capacity in the remaining AZ. If the remaining AZ cannot sustain load, outages can still occur.
- ✓
Add a third Availability Zone so the ALB and Auto Scaling group span at least three AZs.
Why this is correct
An AZ failure typically reduces available capacity to the other AZs. Spreading the ALB subnets and ASG instances across at least three AZs reduces the impact of losing any single AZ and helps ensure the remaining AZs can continue serving traffic.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable instance scale-in protection to stop the ASG from terminating unhealthy instances.
Why it's wrong here
Scale-in protection primarily affects scale-in actions (for example, terminating instances due to decreasing desired capacity). It does not solve the capacity-loss problem during an AZ failure, and it can interfere with replacing instances based on unhealthy status and replacement policies.
- ✗
Switch the ALB to an internal Network Load Balancer (NLB) to avoid cross-AZ traffic.
Why it's wrong here
Changing from ALB to NLB does not provide additional AZ fault tolerance for the compute capacity placement. Cross-AZ traffic considerations are separate from handling an AZ outage.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates think reducing health check timeouts or enabling scale-in protection can compensate for an AZ failure, but AWS explicitly requires a minimum of three AZs to achieve high availability for ALB-based architectures.
Detailed technical explanation
How to think about this question
AWS recommends deploying across at least three AZs for production workloads to meet the 'Design for failure' principle. The ALB distributes traffic evenly across healthy targets in all enabled AZs, and the ASG maintains a desired capacity across AZs; with only two AZs, a single AZ failure can drop capacity below the minimum healthy threshold, causing the ALB to return 503 errors. Under the hood, the ALB uses a per-AZ node that processes traffic for its AZ, and if that AZ fails, the load balancer automatically reroutes traffic to other AZs only if they have sufficient healthy targets—so three AZs provide a buffer against such failures.
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
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
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 a third Availability Zone so the ALB and Auto Scaling group span at least three AZs. — Adding a third Availability Zone (AZ) ensures that the Application Load Balancer (ALB) and Auto Scaling group (ASG) can continue to route traffic and maintain capacity even if one AZ fails. With only two AZs, a single AZ failure reduces the fleet by 50% and may cause the ALB to lose the minimum healthy hosts required to serve traffic. Spreading across three AZs provides a higher resilience margin, as the remaining two AZs can absorb the load while the failed AZ recovers.
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". 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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Last reviewed: Jun 11, 2026
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