- A
Increase the desired capacity in the existing Availability Zone to handle all traffic during an outage.
Why wrong: This increases capacity only in the AZ that is failing. When the AZ outage occurs, instances in that AZ are unavailable regardless of capacity, so there is no redundancy to serve traffic.
- B
Deploy the ALB and the Auto Scaling group across at least two Availability Zones so healthy targets remain.
To tolerate an AZ outage, both the load-balancing entry point (the ALB) and the compute capacity (the Auto Scaling instances) must be available in more than one AZ. With the ALB in multiple AZs and the Auto Scaling group using multiple subnets/AZs, requests can be routed to healthy targets in a remaining AZ while Auto Scaling replaces unhealthy instances.
- C
Enable longer ALB health check intervals so failing instances are detected more slowly.
Why wrong: Adjusting health check intervals affects how quickly the ALB marks targets unhealthy. It does not add additional capacity in another AZ, so it does not address the outage dependency.
- D
Switch from the ALB to an Internet Gateway so instances can fail over to the public internet.
Why wrong: An Internet Gateway provides internet connectivity, but it does not provide multi-AZ application availability. Without a redundant load-balancing and multi-AZ compute setup, an AZ outage still makes the application unavailable.
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 company hosts a web application on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The ALB and the Auto Scaling group are currently deployed in only one Availability Zone (AZ). The business wants the application to keep running if that AZ has an outage. What is the best change?
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.
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
Deploy the ALB and the Auto Scaling group across at least two Availability Zones so healthy targets remain.
Deploying the ALB and Auto Scaling group across at least two Availability Zones (AZs) ensures that if one AZ fails, the ALB can route traffic to healthy EC2 instances in the remaining AZ(s). This is the fundamental AWS best practice for high availability: an ALB is a regional service that requires targets in multiple AZs to survive an AZ outage, and the Auto Scaling group must also span those AZs to maintain capacity. Without multi-AZ deployment, a single AZ failure makes the entire application unavailable regardless of instance health checks.
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 the existing Availability Zone to handle all traffic during an outage.
Why it's wrong here
This increases capacity only in the AZ that is failing. When the AZ outage occurs, instances in that AZ are unavailable regardless of capacity, so there is no redundancy to serve traffic.
- ✓
Deploy the ALB and the Auto Scaling group across at least two Availability Zones so healthy targets remain.
Why this is correct
To tolerate an AZ outage, both the load-balancing entry point (the ALB) and the compute capacity (the Auto Scaling instances) must be available in more than one AZ. With the ALB in multiple AZs and the Auto Scaling group using multiple subnets/AZs, requests can be routed to healthy targets in a remaining AZ while Auto Scaling replaces unhealthy instances.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable longer ALB health check intervals so failing instances are detected more slowly.
Why it's wrong here
Adjusting health check intervals affects how quickly the ALB marks targets unhealthy. It does not add additional capacity in another AZ, so it does not address the outage dependency.
- ✗
Switch from the ALB to an Internet Gateway so instances can fail over to the public internet.
Why it's wrong here
An Internet Gateway provides internet connectivity, but it does not provide multi-AZ application availability. Without a redundant load-balancing and multi-AZ compute setup, an AZ outage still makes the application unavailable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates think increasing capacity or adjusting health check intervals can compensate for a single-AZ deployment, but AWS high availability fundamentally requires distributing resources across multiple isolated failure domains (AZs).
Detailed technical explanation
How to think about this question
An ALB operates at the application layer (Layer 7) and uses DNS-based routing to distribute traffic across targets in multiple AZs; it automatically reroutes traffic away from an impaired AZ when health checks fail. The Auto Scaling group must define a launch template and specify multiple subnets (one per AZ) to ensure instances are distributed; if the group is configured with only one subnet, it cannot launch instances in another AZ even if the ALB spans multiple AZs. In practice, AWS recommends a minimum of two AZs for production workloads to achieve a Service Level Agreement (SLA) of 99.99% for the ALB.
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: Deploy the ALB and the Auto Scaling group across at least two Availability Zones so healthy targets remain. — Deploying the ALB and Auto Scaling group across at least two Availability Zones (AZs) ensures that if one AZ fails, the ALB can route traffic to healthy EC2 instances in the remaining AZ(s). This is the fundamental AWS best practice for high availability: an ALB is a regional service that requires targets in multiple AZs to survive an AZ outage, and the Auto Scaling group must also span those AZs to maintain capacity. Without multi-AZ deployment, a single AZ failure makes the entire application unavailable regardless of instance health checks.
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". 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.
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Last reviewed: Jun 11, 2026
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