- A
Place the Auto Scaling group in subnets across at least two Availability Zones.
Spreading the Auto Scaling group across multiple Availability Zones lets EC2 capacity remain available if one Zone fails. The group can continue launching and serving instances in the remaining healthy Zone, which improves availability without changing the application itself.
- B
Attach the Application Load Balancer to subnets in at least two Availability Zones.
An ALB should span multiple Availability Zones so it can keep receiving traffic even if one Zone becomes unavailable. Elastic Load Balancing automatically routes requests only to healthy targets in surviving Zones, which improves resilience during a Zone outage.
- C
Increase the instance size so each server can handle more traffic alone.
Why wrong: A larger instance may improve capacity, but it does not protect against an Availability Zone failure. If the Zone goes down, all instances in that Zone are still lost regardless of their size.
- D
Disable ALB health checks so instances stay registered longer.
Why wrong: Health checks are useful for removing unhealthy targets quickly. Disabling them would make failover and recovery worse because the load balancer could keep sending traffic to broken instances.
- E
Run the whole stack in one Availability Zone for simpler networking.
Why wrong: A single Availability Zone creates a clear single point of failure. Simplicity may be appealing, but it does not meet the goal of surviving a Zone outage.
Quick Answer
The answer is to attach the Application Load Balancer to subnets in at least two Availability Zones and configure the Auto Scaling group to launch instances across those same subnets. This works because the ALB distributes traffic only to healthy targets in its attached subnets, while the Auto Scaling group automatically replaces failed instances across the specified AZs; if one zone goes down, the remaining AZs absorb the load and the ASG spins up new instances there, maintaining service continuity. On the SAA-C03 exam, this tests your understanding of the fundamental high-availability pattern: redundancy at both the network layer (ALB subnets) and compute layer (ASG subnets). A common trap is thinking that simply enabling multi-AZ on the ALB alone is enough—you must also ensure the ASG spans the same subnets. Remember the mnemonic: “ALB and ASG must share the same AZs to survive a zone’s freeze.”
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 application runs on an Auto Scaling group behind an Application Load Balancer. The business wants the service to keep running if one Availability Zone goes down. Which two changes should you make? Select two.
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
Place the Auto Scaling group in subnets across at least two Availability Zones.
Option A is correct because placing the Auto Scaling group in subnets across at least two Availability Zones ensures that if one AZ fails, the Auto Scaling group can still launch instances in the remaining healthy AZ(s). This is a fundamental pattern for high availability, as the Auto Scaling group distributes instances across the specified subnets, and if an entire AZ becomes unavailable, instances in other AZs continue to serve traffic.
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 subnets across at least two Availability Zones.
Why this is correct
Spreading the Auto Scaling group across multiple Availability Zones lets EC2 capacity remain available if one Zone fails. The group can continue launching and serving instances in the remaining healthy Zone, which improves availability without changing the application itself.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Attach the Application Load Balancer to subnets in at least two Availability Zones.
Why this is correct
An ALB should span multiple Availability Zones so it can keep receiving traffic even if one Zone becomes unavailable. Elastic Load Balancing automatically routes requests only to healthy targets in surviving Zones, which improves resilience during a Zone outage.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the instance size so each server can handle more traffic alone.
Why it's wrong here
A larger instance may improve capacity, but it does not protect against an Availability Zone failure. If the Zone goes down, all instances in that Zone are still lost regardless of their size.
- ✗
Disable ALB health checks so instances stay registered longer.
Why it's wrong here
Health checks are useful for removing unhealthy targets quickly. Disabling them would make failover and recovery worse because the load balancer could keep sending traffic to broken instances.
- ✗
Run the whole stack in one Availability Zone for simpler networking.
Why it's wrong here
A single Availability Zone creates a clear single point of failure. Simplicity may be appealing, but it does not meet the goal of surviving a Zone outage.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think increasing instance size or disabling health checks provides resilience, but AWS's high availability model relies on distributing resources across multiple Availability Zones, not on making individual instances more powerful or ignoring failures.
Detailed technical explanation
How to think about this question
Under the hood, the Application Load Balancer uses a cross-zone load balancing feature (enabled by default) to distribute traffic evenly across healthy targets in all enabled AZs. When you attach the ALB to subnets in at least two AZs, the ALB creates a separate load balancer node in each AZ, allowing it to continue routing traffic even if one node or AZ fails. The Auto Scaling group's health check grace period and the ALB's health checks work together to detect and replace failed instances, but the AZ-level redundancy is what protects against an entire AZ outage.
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
Got this wrong? Here's your next step.
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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: Place the Auto Scaling group in subnets across at least two Availability Zones. — Option A is correct because placing the Auto Scaling group in subnets across at least two Availability Zones ensures that if one AZ fails, the Auto Scaling group can still launch instances in the remaining healthy AZ(s). This is a fundamental pattern for high availability, as the Auto Scaling group distributes instances across the specified subnets, and if an entire AZ becomes unavailable, instances in other AZs continue to serve traffic.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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. 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?
easy- A.Reduce health check timeouts so instances are replaced sooner in the failed AZ.
- ✓ B.Add a third Availability Zone so the ALB and Auto Scaling group span at least three AZs.
- C.Enable instance scale-in protection to stop the ASG from terminating unhealthy instances.
- D.Switch the ALB to an internal Network Load Balancer (NLB) to avoid cross-AZ traffic.
Why B: 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.
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Last reviewed: Jun 11, 2026
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