- A
Update the ASG to use subnet IDs that span at least two Availability Zones so it can launch replacement instances after an AZ outage.
If the ASG is attached to subnets in multiple Availability Zones, when instances in the failed AZ become unhealthy/terminate, Auto Scaling can launch new instances in the remaining AZs to restore the desired capacity. This directly addresses the root cause: the ASG cannot create capacity outside the AZs it is configured for.
- B
Reduce the ALB health check interval to speed up detection of unhealthy targets.
Why wrong: Reducing the ALB health check interval may detect instance health failures sooner, but it does not change where Auto Scaling is allowed to launch instances. If the ASG is still limited to a single AZ’s subnets, capacity cannot be restored in other AZs.
- C
Enable connection draining on the ALB so existing requests complete before targets are terminated.
Why wrong: Connection draining helps during controlled events such as deployments or scale-in, where you want in-flight requests to finish. It does not enable the ASG to launch replacements in other Availability Zones after an AZ outage.
- D
Increase the ASG desired capacity from 2 to 6 to compensate for the missing subnets.
Why wrong: Auto Scaling will still launch instances only into the AZs represented by the ASG’s configured subnets. After the AZ outage, increasing desired capacity does not allow replacement instances to start in a different AZ.
Quick Answer
The answer is to update the Auto Scaling group to use subnet IDs that span at least two Availability Zones. This is correct because an ASG can only launch EC2 instances into the subnets explicitly assigned to it; if those subnets are confined to a single AZ and that AZ fails, the ASG has no capacity to launch replacement instances, even though the ALB remains healthy across multiple AZs. By configuring the ASG with multi-AZ subnets, it can automatically launch instances in a healthy AZ, restoring capacity and resilience directly. On the SAA-C03 exam, this scenario tests your understanding that an ASG’s subnet configuration, not the ALB’s, determines fault tolerance for instance launches—a common trap is assuming the multi-AZ ALB alone ensures resilience. Remember the memory tip: “ASG subnets are the launch pad; if the pad fails, no instance takes off.”
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 company runs an application behind an Application Load Balancer (ALB). An Auto Scaling group (ASG) is configured with desired capacity 2, but it is attached only to subnets in a single Availability Zone. The ALB is healthy because it is configured across multiple Availability Zones.
When the Availability Zone that contains the ASG subnets experiences an outage, what change most directly improves resilience and allows capacity to be restored automatically?
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
Update the ASG to use subnet IDs that span at least two Availability Zones so it can launch replacement instances after an AZ outage.
Option A is correct because an Auto Scaling group (ASG) can only launch instances into the subnets explicitly assigned to it. If those subnets reside in a single Availability Zone (AZ) and that AZ fails, the ASG has no capacity to launch replacement instances, even though the ALB is multi-AZ. By configuring the ASG with subnet IDs spanning at least two AZs, the ASG can automatically launch instances in a healthy AZ, restoring capacity and resilience.
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.
- ✓
Update the ASG to use subnet IDs that span at least two Availability Zones so it can launch replacement instances after an AZ outage.
Why this is correct
If the ASG is attached to subnets in multiple Availability Zones, when instances in the failed AZ become unhealthy/terminate, Auto Scaling can launch new instances in the remaining AZs to restore the desired capacity. This directly addresses the root cause: the ASG cannot create capacity outside the AZs it is configured for.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Reduce the ALB health check interval to speed up detection of unhealthy targets.
Why it's wrong here
Reducing the ALB health check interval may detect instance health failures sooner, but it does not change where Auto Scaling is allowed to launch instances. If the ASG is still limited to a single AZ’s subnets, capacity cannot be restored in other AZs.
- ✗
Enable connection draining on the ALB so existing requests complete before targets are terminated.
Why it's wrong here
Connection draining helps during controlled events such as deployments or scale-in, where you want in-flight requests to finish. It does not enable the ASG to launch replacements in other Availability Zones after an AZ outage.
- ✗
Increase the ASG desired capacity from 2 to 6 to compensate for the missing subnets.
Why it's wrong here
Auto Scaling will still launch instances only into the AZs represented by the ASG’s configured subnets. After the AZ outage, increasing desired capacity does not allow replacement instances to start in a different AZ.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a multi-AZ ALB automatically makes the entire architecture resilient, overlooking that the ASG must also be configured with subnets in multiple AZs to launch replacement instances after an AZ failure.
Detailed technical explanation
How to think about this question
An ASG's subnet configuration determines the AZs where instances can be launched; if subnets are in only one AZ, the ASG is effectively single-AZ regardless of the ALB's multi-AZ setup. During an AZ outage, the ASG's health checks (EC2 status checks or ELB health checks) mark instances as unhealthy, triggering a scale-in event, but without subnets in a healthy AZ, the ASG cannot scale out. This scenario highlights the importance of aligning ASG subnet configuration with the ALB's AZ distribution to ensure fault tolerance.
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
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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: Update the ASG to use subnet IDs that span at least two Availability Zones so it can launch replacement instances after an AZ outage. — Option A is correct because an Auto Scaling group (ASG) can only launch instances into the subnets explicitly assigned to it. If those subnets reside in a single Availability Zone (AZ) and that AZ fails, the ASG has no capacity to launch replacement instances, even though the ALB is multi-AZ. By configuring the ASG with subnet IDs spanning at least two AZs, the ASG can automatically launch instances in a healthy AZ, restoring capacity and resilience.
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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Last reviewed: Jun 11, 2026
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.
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