- A
Reduce the ASG desired capacity by 1 and rely on the ALB to route traffic to fewer instances during the outage.
Why wrong: Reducing desired capacity makes the ASG intentionally maintain less capacity. It does not address why instances are not being replaced, so capacity may not recover automatically to the original level after the outage.
- B
Configure the ASG to use the ALB target-group health checks (ELB/target-group health) and ensure the ASG has at least two subnets in different Availability Zones that remain available for instance placement.
If the AZ outage prevents the ALB from reaching targets, instance-level (EC2) health checks may still consider instances “healthy” because the instances are running. When the ASG is configured to use ALB/target-group health (ASG health check type set to ELB and tied to the target group), the ASG can detect application-level unreachability and replace unhealthy instances. With multiple eligible subnets across different AZs, the ASG can launch replacement instances in the remaining AZs and automatically return to the configured desired capacity.
- C
Move the ALB to only one subnet so health checks and routing remain consistent during the outage.
Why wrong: An ALB can only route traffic through the load balancer nodes placed in the selected subnets/AZs. If the single selected subnet/AZ is affected, the ALB can become unavailable even if the ASG launches healthy instances elsewhere.
- D
Add an S3 event trigger to terminate unhealthy instances so the ASG can scale back out using its scheduled actions.
Why wrong: S3 events do not correlate with ALB target health or Availability Zone failures for EC2 instances. Scheduled scaling actions may also not run immediately in response to health deterioration, so this approach will not directly fix the recovery mechanism.
Quick Answer
The answer is to configure the ASG to use the ALB target-group health checks and ensure the ASG spans at least two subnets in different Availability Zones that remain available. This works because the ALB’s health checks continuously monitor each instance’s ability to serve traffic; when an AZ fails, those instances fail the health check, and the ASG—now using the ELB/target-group health check type—immediately marks them unhealthy and launches replacement instances in the remaining healthy AZs. On the SAA-C03 exam, this scenario tests your understanding of how ASG automatic capacity recovery depends on both the health check type and subnet diversity—a common trap is assuming the default EC2 status checks alone will trigger replacement, but those only detect instance-level failures, not AZ-level impairment. The key insight is that ALB health checks provide application-level awareness, while multi-AZ subnets give the ASG a place to launch replacements. Memory tip: “ALB checks the app, ASG fills the gap—two AZs keep the stack.”
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 web app runs on an EC2 Auto Scaling group behind an Application Load Balancer (ALB). The ALB is configured with health checks and the ASG spans three subnets in three Availability Zones. During an AZ outage, monitoring shows the number of healthy instances drops sharply and never returns to the original capacity until the ASG is manually adjusted. What change most directly improves resilience so capacity returns automatically during an AZ failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"never"Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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
Configure the ASG to use the ALB target-group health checks (ELB/target-group health) and ensure the ASG has at least two subnets in different Availability Zones that remain available for instance placement.
Option B is correct because configuring the ASG to use ALB target-group health checks (ELB health checks) ensures that the ASG replaces instances that fail the ALB's health checks, including those in an impaired AZ. By also ensuring the ASG has at least two subnets in different AZs that remain available, the ASG can launch replacement instances in the healthy AZs when one AZ fails, automatically restoring capacity without manual intervention.
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 the ASG desired capacity by 1 and rely on the ALB to route traffic to fewer instances during the outage.
Why it's wrong here
Reducing desired capacity makes the ASG intentionally maintain less capacity. It does not address why instances are not being replaced, so capacity may not recover automatically to the original level after the outage.
- ✓
Configure the ASG to use the ALB target-group health checks (ELB/target-group health) and ensure the ASG has at least two subnets in different Availability Zones that remain available for instance placement.
Why this is correct
If the AZ outage prevents the ALB from reaching targets, instance-level (EC2) health checks may still consider instances “healthy” because the instances are running. When the ASG is configured to use ALB/target-group health (ASG health check type set to ELB and tied to the target group), the ASG can detect application-level unreachability and replace unhealthy instances. With multiple eligible subnets across different AZs, the ASG can launch replacement instances in the remaining AZs and automatically return to the configured desired capacity.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Move the ALB to only one subnet so health checks and routing remain consistent during the outage.
Why it's wrong here
An ALB can only route traffic through the load balancer nodes placed in the selected subnets/AZs. If the single selected subnet/AZ is affected, the ALB can become unavailable even if the ASG launches healthy instances elsewhere.
- ✗
Add an S3 event trigger to terminate unhealthy instances so the ASG can scale back out using its scheduled actions.
Why it's wrong here
S3 events do not correlate with ALB target health or Availability Zone failures for EC2 instances. Scheduled scaling actions may also not run immediately in response to health deterioration, so this approach will not directly fix the recovery mechanism.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume EC2 status checks are sufficient for AZ failure detection, but they fail to recognize that an instance in a failed AZ may still pass EC2 status checks while being unreachable via the network, so only ALB target-group health checks trigger the ASG to replace them.
Detailed technical explanation
How to think about this question
When an AZ fails, the ALB marks all instances in that AZ as unhealthy via its health checks. If the ASG uses EC2 status checks only, it may not detect the failure because the instances are still running (just unreachable). By using ELB health checks, the ASG sees the health check failures and terminates the instances, then launches new ones in the remaining healthy AZs, provided the ASG's subnet configuration includes at least two AZs. The ASG's 'Availability Zone rebalancing' feature then redistributes instances across the remaining AZs to maintain balance.
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
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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: Configure the ASG to use the ALB target-group health checks (ELB/target-group health) and ensure the ASG has at least two subnets in different Availability Zones that remain available for instance placement. — Option B is correct because configuring the ASG to use ALB target-group health checks (ELB health checks) ensures that the ASG replaces instances that fail the ALB's health checks, including those in an impaired AZ. By also ensuring the ASG has at least two subnets in different AZs that remain available, the ASG can launch replacement instances in the healthy AZs when one AZ fails, automatically restoring capacity without manual intervention.
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: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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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