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
Current deployment:
Application Load Balancer subnets: subnet-a1 (AZ-a), subnet-a2 (AZ-a)
Auto Scaling group subnets: subnet-a1 (AZ-a) only
Desired capacity: 4 instances
Minimum capacity: 4 instances
Incident report:
2026-04-18T09:21Z AZ-a experienced a power issue
2026-04-18T09:22Z all targets became unhealthy
2026-04-18T09:25Z service returned HTTP 503 to users
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
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.
Exhibit
Current deployment:
Application Load Balancer subnets: subnet-a1 (AZ-a), subnet-a2 (AZ-a)
Auto Scaling group subnets: subnet-a1 (AZ-a) only
Desired capacity: 4 instances
Minimum capacity: 4 instances
Incident report:
2026-04-18T09:21Z AZ-a experienced a power issue
2026-04-18T09:22Z all targets became unhealthy
2026-04-18T09:25Z service returned HTTP 503 to users
A
Increase the desired capacity in AZ-a so more instances can absorb the failure of that same Availability Zone.
Why wrong: Adding more instances in the same Availability Zone does not protect against an AZ-wide outage because all of those instances fail together.
B
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
A resilient design needs the load balancer and the Auto Scaling group to span multiple Availability Zones. If one AZ fails, the ALB can still route to healthy targets in the remaining AZs and the Auto Scaling group can replenish capacity there. This is the simplest and most common way to achieve AZ-level fault tolerance.
C
Disable health checks so the ALB stops removing targets during brief infrastructure issues.
Why wrong: Disabling health checks hides failures instead of recovering from them. The load balancer would continue sending traffic to unhealthy targets, which makes the outage worse rather than better.
D
Move the application to a single larger instance type so the fleet has fewer moving parts.
Why wrong: A single larger instance increases concentration risk and does not remove the Availability Zone single point of failure. It reduces the number of instances, but it also reduces redundancy.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
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.
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 the desired capacity in AZ-a so more instances can absorb the failure of that same Availability Zone.
Why it's wrong here
Adding more instances in the same Availability Zone does not protect against an AZ-wide outage because all of those instances fail together.
✓
Add at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group.
Why this is correct
A resilient design needs the load balancer and the Auto Scaling group to span multiple Availability Zones. If one AZ fails, the ALB can still route to healthy targets in the remaining AZs and the Auto Scaling group can replenish capacity there. This is the simplest and most common way to achieve AZ-level fault tolerance.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable health checks so the ALB stops removing targets during brief infrastructure issues.
Why it's wrong here
Disabling health checks hides failures instead of recovering from them. The load balancer would continue sending traffic to unhealthy targets, which makes the outage worse rather than better.
✗
Move the application to a single larger instance type so the fleet has fewer moving parts.
Why it's wrong here
A single larger instance increases concentration risk and does not remove the Availability Zone single point of failure. It reduces the number of instances, but it also reduces redundancy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think increasing capacity in a single AZ (Option A) provides resilience, but it actually concentrates risk in that AZ, while the correct answer requires distributing resources across multiple AZs to achieve true fault tolerance.
Detailed technical explanation
How to think about this question
Under the hood, an Application Load Balancer (ALB) is a regional service that can route traffic to targets in multiple AZs, but it must have at least one subnet in each AZ where targets reside to enable cross-zone load balancing. The Auto Scaling group uses the subnets specified in its launch configuration to launch instances; by adding subnets from a second AZ, the group can automatically replace failed instances in a different AZ, leveraging the ALB's health check mechanism (HTTP/HTTPS health checks on the configured path) to detect and reroute traffic away from unhealthy targets. In a real-world scenario, this design is critical for meeting SLAs that require 99.99% availability, as it withstands an entire AZ outage without manual intervention.
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.
Visual reference
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 at least one subnet from a second Availability Zone to both the ALB and the Auto Scaling group. — 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.
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: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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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, the web application must remain available even if one Availability Zone fails. What is the best change to improve resilience with the least redesign?
medium
A.Increase DesiredCapacity to 4 while keeping all instances in subnet-a1.
✓ B.Add subnet-b1 in a different Availability Zone to the Auto Scaling group.
C.Replace the Application Load Balancer with a Network Load Balancer.
D.Enable EBS encryption on the launch template volumes.
Why B: 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.
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, 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 4. 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 5. 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 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 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.
Variation 7. 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
✓ A.Application Load Balancer (ALB): Distributes incoming traffic across healthy targets in multiple Availability Zones.
✓ B.Auto Scaling group: Maintains desired instance count across multiple Availability Zones by replacing failed instances.
✓ C.Multi-AZ RDS: Synchronously replicates data to a standby instance in a different Availability Zone for automatic failover.
✓ D.Amazon Route 53: DNS routing with health checks to redirect traffic away from unhealthy resources in a failed Availability Zone.
F.Auto Scaling group: Distributes incoming traffic across healthy instances in multiple Availability Zones.
Why A: 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 8. 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
✓ A.Elastic Load Balancer: Distributes incoming traffic across multiple targets in multiple Availability Zones
✓ B.Auto Scaling Group: Automatically replaces unhealthy instances and maintains desired capacity across Availability Zones
✓ C.Amazon RDS Multi-AZ: Provides automatic failover to a standby database instance in a different Availability Zone
✓ D.Amazon Route 53: Routes end users to healthy endpoints using DNS health checks and failover
E.Amazon S3: Automatically fails over to a secondary region in case of an Availability Zone failure
F.AWS CloudFormation: Distributes application load across multiple Availability Zones
Why A: 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.
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