- A
Keep the ASG in one subnet/AZ, but enable ALB stickiness to reduce session interruption.
Why wrong: Stickiness affects session routing but does not create targets in a second AZ during an AZ outage.
- B
Update the ASG to launch instances across subnets in at least two Availability Zones and ensure ALB health checks target an application-ready path.
Spreading instances across multiple AZs ensures the ALB can route to healthy targets even when one AZ fails.
- C
Add a NAT gateway in the public subnets so instances can reach the internet during maintenance events.
Why wrong: NAT affects outbound connectivity, not target placement or health during an AZ outage.
- D
Create a second ALB in the same Availability Zone and route traffic using DNS failover.
Why wrong: DNS failover adds complexity and still depends on healthy targets; without multi-AZ instances, failover won’t help much.
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. A key principle to apply: auto Scaling groups can be configured to launch instances across multiple Availability Zones.. 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 stateless web API runs on EC2 instances behind an Application Load Balancer (ALB). The Auto Scaling group (ASG) currently uses subnets from only one Availability Zone, even though the ALB spans two Availability Zones. During maintenance of that single AZ, the ALB remains up but clients see timeouts because there are no healthy targets. Which change most directly improves resilience against an AZ failure?
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 launch instances across subnets in at least two Availability Zones and ensure ALB health checks target an application-ready path.
Option B is correct because it directly addresses the single point of failure: the ASG only launches instances in one AZ, so when that AZ fails, the ALB has no healthy targets to route traffic to, causing timeouts. By configuring the ASG to span at least two AZs, the ALB can distribute traffic to healthy instances in the remaining AZ during maintenance, ensuring high availability. The ALB health check must target an application-ready path (e.g., /health) to accurately detect instance health and avoid routing requests to impaired instances.
Key principle: Auto Scaling groups can be configured to launch instances across multiple Availability Zones.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Keep the ASG in one subnet/AZ, but enable ALB stickiness to reduce session interruption.
Why it's wrong here
Stickiness affects session routing but does not create targets in a second AZ during an AZ outage.
- ✓
Update the ASG to launch instances across subnets in at least two Availability Zones and ensure ALB health checks target an application-ready path.
Why this is correct
Spreading instances across multiple AZs ensures the ALB can route to healthy targets even when one AZ fails.
Related concept
Auto Scaling groups can be configured to launch instances across multiple Availability Zones.
- ✗
Add a NAT gateway in the public subnets so instances can reach the internet during maintenance events.
Why it's wrong here
NAT affects outbound connectivity, not target placement or health during an AZ outage.
- ✗
Create a second ALB in the same Availability Zone and route traffic using DNS failover.
Why it's wrong here
DNS failover adds complexity and still depends on healthy targets; without multi-AZ instances, failover won’t help much.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think ALB stickiness or DNS failover can compensate for a single-AZ deployment, but AWS explicitly requires multi-AZ architecture for resilience, and the ALB's health check must be application-aware to avoid routing to impaired instances.
Detailed technical explanation
How to think about this question
Under the hood, an ALB is inherently regional and can route traffic to targets across multiple AZs, but it requires the ASG to launch instances in those AZs to provide fault isolation. The ALB's health checks use HTTP/HTTPS or TCP probes; if the health check path is not application-aware (e.g., just a TCP ping), the ALB may consider an instance healthy even if the application is unresponsive, leading to timeouts. In a real-world scenario, an AZ failure in us-east-1a could take down all instances, but if the ASG spans us-east-1b, the ALB automatically reroutes traffic to healthy instances in that AZ, maintaining service continuity.
KKey Concepts to Remember
- Auto Scaling groups can be configured to launch instances across multiple Availability Zones.
- Application Load Balancers distribute traffic to healthy targets across all configured AZs.
- Multi-AZ deployments are a primary strategy for achieving high availability and fault tolerance.
- ALB health checks determine if an instance is ready to receive traffic, preventing routing to unhealthy targets.
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
Auto Scaling groups can be configured to launch instances across multiple Availability Zones.
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.
Review auto Scaling groups can be configured to launch instances across multiple Availability Zones., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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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 — Auto Scaling groups can be configured to launch instances across multiple Availability Zones..
What is the correct answer to this question?
The correct answer is: Update the ASG to launch instances across subnets in at least two Availability Zones and ensure ALB health checks target an application-ready path. — Option B is correct because it directly addresses the single point of failure: the ASG only launches instances in one AZ, so when that AZ fails, the ALB has no healthy targets to route traffic to, causing timeouts. By configuring the ASG to span at least two AZs, the ALB can distribute traffic to healthy instances in the remaining AZ during maintenance, ensuring high availability. The ALB health check must target an application-ready path (e.g., /health) to accurately detect instance health and avoid routing requests to impaired instances.
What should I do if I get this SAA-C03 question wrong?
Review auto Scaling groups can be configured to launch instances across multiple Availability Zones., then practise related SAA-C03 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Auto Scaling groups can be configured to launch instances across multiple Availability Zones.
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Last reviewed: Jun 11, 2026
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