- A
Place the Auto Scaling group in only one subnet so instance launches are simpler.
Why wrong: Using only one subnet/AZ removes redundancy. An AZ outage would still take down capacity until manual action occurs.
- B
Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
Spreading the ALB and Auto Scaling group across at least two AZs provides redundant capacity. If one AZ fails, the ALB continues routing to healthy targets in the other AZ.
- C
Increase the target group deregistration delay to allow old instances to stay longer.
Why wrong: Changing deregistration delay affects connection draining, not capacity placement across AZs. It doesn’t create additional resilient instances.
- D
Use a Network Load Balancer, but keep all subnets in a single Availability Zone.
Why wrong: Switching load balancer type doesn’t fix the root cause. If capacity is only in one AZ, failures will still impact the service.
Quick Answer
The answer is to ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones. This configuration directly enables automatic failover for the compute layer because the Application Load Balancer can immediately reroute traffic to healthy targets in surviving AZs when one zone fails, while the Auto Scaling group automatically launches replacement instances in those remaining AZs without manual intervention. On the SAA-C03 exam, this scenario tests your understanding of how multi-AZ architecture provides high availability at the compute layer, and a common trap is assuming that simply enabling cross-zone load balancing or adding more instances within a single AZ is sufficient. Remember the key principle: for automatic failover, both the ALB and the Auto Scaling group must be explicitly configured across at least two AZs. A useful memory tip is “two zones, no phone calls”—meaning with two AZs, you never have to manually call in replacements.
SAA-C03 Design Resilient Architectures Practice Question
This SAA-C03 practice question tests your understanding of design resilient architectures. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
An engineering team deploys a stateless web API on EC2 using an Auto Scaling group and an Application Load Balancer (ALB). During a recent test, they noticed that when one Availability Zone was unavailable, traffic failed until new instances were manually launched. Which change most directly improves automatic failover for the compute layer within a single Region?
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
Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
Option B is correct because an Application Load Balancer (ALB) and Auto Scaling group must span multiple subnets in at least two Availability Zones (AZs) to provide automatic failover. When one AZ becomes unavailable, the ALB automatically reroutes traffic to healthy targets in the remaining AZs, and the Auto Scaling group can launch replacement instances in the surviving AZs. This architecture ensures that the compute layer remains available 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.
- ✗
Place the Auto Scaling group in only one subnet so instance launches are simpler.
Why it's wrong here
Using only one subnet/AZ removes redundancy. An AZ outage would still take down capacity until manual action occurs.
- ✓
Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
Why this is correct
Spreading the ALB and Auto Scaling group across at least two AZs provides redundant capacity. If one AZ fails, the ALB continues routing to healthy targets in the other AZ.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the target group deregistration delay to allow old instances to stay longer.
Why it's wrong here
Changing deregistration delay affects connection draining, not capacity placement across AZs. It doesn’t create additional resilient instances.
- ✗
Use a Network Load Balancer, but keep all subnets in a single Availability Zone.
Why it's wrong here
Switching load balancer type doesn’t fix the root cause. If capacity is only in one AZ, failures will still impact the service.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think a single-AZ deployment with a load balancer provides failover, but without multiple AZs, the load balancer itself becomes a single point of failure and cannot reroute traffic when the AZ goes down.
Detailed technical explanation
How to think about this question
Under the hood, the ALB uses a DNS-based endpoint that resolves to multiple IP addresses, one per AZ subnet. When an AZ fails, the ALB health checks mark targets in that AZ as unhealthy and stops sending traffic to them, while the Auto Scaling group detects the missing capacity and launches new instances in the remaining AZs. This behavior is governed by the ALB's cross-zone load balancing setting (enabled by default) and the Auto Scaling group's 'Availability Zones' configuration, which must list at least two AZs for automatic recovery.
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: Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones. — Option B is correct because an Application Load Balancer (ALB) and Auto Scaling group must span multiple subnets in at least two Availability Zones (AZs) to provide automatic failover. When one AZ becomes unavailable, the ALB automatically reroutes traffic to healthy targets in the remaining AZs, and the Auto Scaling group can launch replacement instances in the surviving AZs. This architecture ensures that the compute layer remains available 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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Same concept, more angles
1 more ways this is tested on SAA-C03
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineering team deploys a stateless web API on EC2 using an Auto Scaling group and an Application Load Balancer (ALB). During a recent test, they noticed that when one Availability Zone was unavailable, traffic failed until new instances were manually launched. Which change most directly improves automatic failover for the compute layer within a single Region?
easy- A.Place the Auto Scaling group in only one subnet so instance launches are simpler.
- ✓ B.Ensure the ALB and Auto Scaling group span multiple subnets in at least two Availability Zones.
- C.Increase the target group deregistration delay to allow old instances to stay longer.
- D.Use a Network Load Balancer, but keep all subnets in a single Availability Zone.
Why B: Option B is correct because placing both the ALB and the Auto Scaling group across multiple subnets in at least two Availability Zones ensures that if one AZ becomes unavailable, the ALB can route traffic to healthy instances in the remaining AZs, and the Auto Scaling group can automatically launch replacement instances in the other AZs. This directly provides automatic failover for the compute layer within a single Region without manual intervention.
Last reviewed: Jun 11, 2026
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