The answer is to add subnet-b1 in a different Availability Zone to the Auto Scaling group. This directly improves multi-AZ auto scaling group resilience by ensuring EC2 instances are distributed across two distinct Availability Zones, so if one zone fails, the Application Load Balancer can route traffic to healthy instances in the surviving zone. On the SAA-C03 exam, this scenario tests your understanding that resilience is achieved through zone-level redundancy, not by scaling instance sizes or modifying the load balancer. A common trap is to overcomplicate the solution by redesigning the architecture—such as adding a second load balancer—when the simplest fix is to expand the subnet configuration. Remember the key principle: for high availability, always spread your Auto Scaling group across at least two Availability Zones. Memory tip: “Two zones, no throne—if one zone is gone, the app lives on.”
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.
Exhibit
Application Load Balancer
Subnets: subnet-a1 (us-east-1a), subnet-b1 (us-east-1b)
Auto Scaling group
VPCZoneIdentifier: subnet-a1 (us-east-1a)
DesiredCapacity: 2
MinSize: 2
MaxSize: 4
CloudWatch
HealthyHostCount: 2
HTTPCode_Target_5XX_Count: 0
Troubleshooting note
A planned test that disabled us-east-1a caused the application to become unreachable.
Based on the exhibit, the web application must remain available even if one Availability Zone fails. What is the best change to improve resilience with the least redesign?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Application Load Balancer
Subnets: subnet-a1 (us-east-1a), subnet-b1 (us-east-1b)
Auto Scaling group
VPCZoneIdentifier: subnet-a1 (us-east-1a)
DesiredCapacity: 2
MinSize: 2
MaxSize: 4
CloudWatch
HealthyHostCount: 2
HTTPCode_Target_5XX_Count: 0
Troubleshooting note
A planned test that disabled us-east-1a caused the application to become unreachable.
A
Increase DesiredCapacity to 4 while keeping all instances in subnet-a1.
Why wrong: This adds more instances, but they are still all in the same Availability Zone. If us-east-1a fails, every instance is lost together and the application still goes down. Capacity is not the same as fault isolation.
B
Add subnet-b1 in a different Availability Zone to the Auto Scaling group.
This spreads EC2 instances across two Availability Zones, so the Auto Scaling group can continue serving traffic if one AZ becomes unavailable. Because the ALB is already deployed in both subnets, this is the smallest change that adds true zonal resilience to the compute tier.
C
Replace the Application Load Balancer with a Network Load Balancer.
Why wrong: A Network Load Balancer changes the load-balancing layer, but it does not fix the root problem: all instances are still in one AZ. If that AZ fails, there are still no healthy targets to receive traffic.
D
Enable EBS encryption on the launch template volumes.
Why wrong: EBS encryption improves data protection at rest, but it does not affect availability or failover behavior. The instances would still be concentrated in a single Availability Zone.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add subnet-b1 in a different Availability Zone to the Auto Scaling group.
Adding subnet-b1 in a different Availability Zone to the Auto Scaling group ensures that EC2 instances are launched across two Availability Zones. If one zone fails, the ALB can route traffic to healthy instances in the other zone, maintaining application availability. This change requires minimal redesign because it only modifies the Auto Scaling group's subnet configuration without altering the load balancer or compute architecture.
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.
✗
Increase DesiredCapacity to 4 while keeping all instances in subnet-a1.
Why it's wrong here
This adds more instances, but they are still all in the same Availability Zone. If us-east-1a fails, every instance is lost together and the application still goes down. Capacity is not the same as fault isolation.
✓
Add subnet-b1 in a different Availability Zone to the Auto Scaling group.
Why this is correct
This spreads EC2 instances across two Availability Zones, so the Auto Scaling group can continue serving traffic if one AZ becomes unavailable. Because the ALB is already deployed in both subnets, this is the smallest change that adds true zonal resilience to the compute tier.
Clue confirmation
The clue words "best", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replace the Application Load Balancer with a Network Load Balancer.
Why it's wrong here
A Network Load Balancer changes the load-balancing layer, but it does not fix the root problem: all instances are still in one AZ. If that AZ fails, there are still no healthy targets to receive traffic.
✗
Enable EBS encryption on the launch template volumes.
Why it's wrong here
EBS encryption improves data protection at rest, but it does not affect availability or failover behavior. The instances would still be concentrated in a single Availability Zone.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think increasing instance count or changing load balancer type improves resilience, but without multi-AZ distribution, a single AZ failure still causes a total outage.
Detailed technical explanation
How to think about this question
Auto Scaling groups distribute instances across subnets in different Availability Zones based on the subnet list provided in the launch configuration or template. The ALB automatically registers instances from all subnets and performs health checks; if an entire AZ becomes impaired, the ALB stops routing traffic to instances in that zone. This design aligns with the AWS Well-Architected Framework's 'Design for failure' principle, where redundancy at the AZ level is a foundational pattern for high availability.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Add subnet-b1 in a different Availability Zone to the Auto Scaling group. — Adding subnet-b1 in a different Availability Zone to the Auto Scaling group ensures that EC2 instances are launched across two Availability Zones. If one zone fails, the ALB can route traffic to healthy instances in the other zone, maintaining application availability. This change requires minimal redesign because it only modifies the Auto Scaling group's subnet configuration without altering the load balancer or compute architecture.
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: "best", "least". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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 →
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. Based on the exhibit, a web application must stay available if one Availability Zone fails. What is the best change to improve resilience?
easy
A.Increase the desired capacity to 8 instances in the same subnet.
✓ B.Add a subnet in another Availability Zone to the Auto Scaling group and keep the ALB spanning both AZs.
C.Replace the Application Load Balancer with a Network Load Balancer.
D.Move the instances to a larger instance type with more CPU and memory.
Why B: Adding a subnet in another Availability Zone (AZ) to the Auto Scaling group and keeping the ALB spanning both AZs ensures that if one AZ fails, the ALB can route traffic to healthy instances in the other AZ. This is the standard pattern for building multi-AZ resilient architectures with Auto Scaling and ALB, as it eliminates the single point of failure at the AZ level.
Variation 2. Based on the exhibit, a web application must stay available if one Availability Zone fails. What is the best change to improve resilience?
easy
A.Increase the desired capacity to 8 instances in the same subnet.
✓ B.Add a subnet in another Availability Zone to the Auto Scaling group and keep the ALB spanning both AZs.
C.Replace the Application Load Balancer with a Network Load Balancer.
D.Move the instances to a larger instance type with more CPU and memory.
Why B: Adding a subnet in another Availability Zone (AZ) to the Auto Scaling group and keeping the ALB spanning both AZs ensures that if one AZ fails, the ALB can route traffic to healthy instances in the other AZ. This is the standard pattern for building multi-AZ resilient architectures with Auto Scaling and ALB, as it eliminates the single point of failure at the AZ level.
Variation 3. Based on the exhibit, the application should continue serving requests if one Availability Zone fails. Which change best improves resilience with the least operational complexity?
medium
A.Increase the desired capacity in AZ-a so more instances can absorb the failure of that same Availability Zone.
✓ B.Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
C.Disable health checks so the ALB stops removing targets during brief infrastructure issues.
D.Move the application to a single larger instance type so the fleet has fewer moving parts.
Why B: Option B is correct because adding subnets from a second Availability Zone to both the ALB and the Auto Scaling group distributes the application across multiple AZs. This ensures that if one AZ fails, the ALB can route traffic to healthy targets in the remaining AZ, and the Auto Scaling group can maintain capacity by launching instances in the surviving AZ. This approach directly addresses the requirement to continue serving requests during an AZ failure with minimal operational complexity.
Variation 4. A team wants a web application to keep serving traffic if one Availability Zone fails. Match each architecture element to the resilience behavior it provides.
medium
Why : These pairs match architecture elements with their resilience behaviors for surviving an Availability Zone failure, focusing on AWS services that provide high availability and fault tolerance.
Variation 5. A team wants a web application to keep serving traffic if one Availability Zone fails. Match each architecture element to the resilience behavior it provides.
medium
Why : These pairs match architecture elements with their resilience behaviors for surviving an Availability Zone failure, focusing on AWS services that provide high availability and fault tolerance.
Variation 6. A trading dashboard runs on EC2 instances behind an Application Load Balancer. The design must tolerate the failure of one Availability Zone. What should the Auto Scaling group configuration include? The design must avoid adding custom operational scripts.
medium
A.A single EC2 instance with detailed monitoring
✓ B.Subnets in at least two Availability Zones with health checks enabled
C.All instances in one larger subnet
D.A Network Load Balancer in one subnet
Why B: Option B is correct because distributing EC2 instances across at least two Availability Zones (AZs) ensures that the Auto Scaling group can maintain capacity even if one AZ fails. Enabling health checks on the Application Load Balancer (ALB) allows the group to automatically replace unhealthy instances without custom scripts, meeting the fault-tolerance requirement.
Variation 7. A trading dashboard runs on EC2 instances behind an Application Load Balancer. The design must tolerate the failure of one Availability Zone. What should the Auto Scaling group configuration include?
medium
A.A single EC2 instance with detailed monitoring
✓ B.Subnets in at least two Availability Zones with health checks enabled
C.All instances in one larger subnet
D.A Network Load Balancer in one subnet
Why B: Option B is correct because distributing EC2 instances across subnets in at least two Availability Zones ensures that if one AZ fails, the Auto Scaling group can maintain capacity using instances in the remaining AZ(s). Enabling health checks allows the group to detect and replace unhealthy instances, which is essential for fault tolerance. This configuration meets the requirement to tolerate the failure of one Availability Zone.
Variation 8. A trading dashboard runs on EC2 instances behind an Application Load Balancer. The design must tolerate the failure of one Availability Zone. What should the Auto Scaling group configuration include? The team wants the control to be enforceable during normal operations.
medium
A.A single EC2 instance with detailed monitoring
✓ B.Subnets in at least two Availability Zones with health checks enabled
C.All instances in one larger subnet
D.A Network Load Balancer in one subnet
Why B: Option B is correct because distributing EC2 instances across at least two Availability Zones (AZs) ensures that if one AZ fails, the Auto Scaling group can maintain capacity in the remaining AZ(s). Enabling health checks allows the group to detect instance failures and automatically replace them, providing fault tolerance. This configuration meets the requirement to tolerate a single AZ failure while remaining enforceable during normal operations.
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