- A
Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
An Auto Scaling Group across multiple AZs ensures healthy capacity exists when an AZ becomes impaired, and the ALB can route to instances in any available AZ.
- B
Switch from RDS Single-AZ to RDS Multi-AZ, keeping the EC2 instances in only AZ-a because failover will still reach them.
Why wrong: RDS failover helps database availability, but the observed checkout delay stems from lack of compute capacity in the impaired AZ.
- C
Terminate the ALB and use a Network Load Balancer (NLB) in front of the existing single-AZ EC2 instances.
Why wrong: Changing load balancer type does not fix the dependency on instances only in AZ-a, so recovery will still be impacted.
- D
Add more EC2 instances in AZ-a and increase the ALB health check thresholds to avoid unnecessary replacements during impairments.
Why wrong: Overprovisioning in a single AZ reduces but does not eliminate unavailability when that AZ is degraded and cannot serve traffic.
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 (ASGs) automatically adjust EC2 capacity.. 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.
Your ecommerce app runs behind an Application Load Balancer (ALB) and uses an RDS database for orders. During an AZ impairment in us-east-1, customers report that checkout takes several minutes to recover. The current design places EC2 instances only in private subnets of AZ-a, while the ALB spans multiple subnets. The RDS DB instance is Multi-AZ. Management wants automatic recovery within the same Region.
Which change best addresses the issue with minimal operational overhead?
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
Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
The correct answer is A because the current design has a single point of failure: all EC2 instances are in one Availability Zone (AZ-a). During an AZ impairment, those instances become unreachable, causing the checkout process to fail until the impairment ends or manual intervention occurs. By placing EC2 instances in an Auto Scaling Group spanning at least two AZs, the application can automatically recover by launching new instances in a healthy AZ, while the ALB distributes traffic across the surviving AZs. This minimizes operational overhead as Auto Scaling handles instance replacement automatically.
Key principle: Auto Scaling Groups (ASGs) automatically adjust EC2 capacity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
Why this is correct
An Auto Scaling Group across multiple AZs ensures healthy capacity exists when an AZ becomes impaired, and the ALB can route to instances in any available AZ.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Auto Scaling Groups (ASGs) automatically adjust EC2 capacity.
- ✗
Switch from RDS Single-AZ to RDS Multi-AZ, keeping the EC2 instances in only AZ-a because failover will still reach them.
Why it's wrong here
RDS failover helps database availability, but the observed checkout delay stems from lack of compute capacity in the impaired AZ.
- ✗
Terminate the ALB and use a Network Load Balancer (NLB) in front of the existing single-AZ EC2 instances.
Why it's wrong here
Changing load balancer type does not fix the dependency on instances only in AZ-a, so recovery will still be impacted.
- ✗
Add more EC2 instances in AZ-a and increase the ALB health check thresholds to avoid unnecessary replacements during impairments.
Why it's wrong here
Overprovisioning in a single AZ reduces but does not eliminate unavailability when that AZ is degraded and cannot serve traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on the database layer (Multi-AZ) or load balancer type (NLB vs ALB) and overlook the critical single-AZ EC2 instance placement, which is the actual bottleneck causing the prolonged recovery during an AZ impairment.
Detailed technical explanation
How to think about this question
Under the hood, an ALB performs health checks against targets in each AZ and only routes traffic to healthy targets in healthy AZs. When an AZ fails, the ALB automatically stops sending traffic to that AZ's targets, but if all targets are in that single AZ, the ALB returns 503 errors. Auto Scaling Groups with a multi-AZ strategy use Amazon EC2 Auto Scaling to maintain a minimum number of instances across AZs, and when an AZ is impaired, the ASG launches replacement instances in the remaining AZs, leveraging the ALB's cross-zone load balancing to distribute traffic. This design aligns with the AWS Well-Architected Framework's principle of 'Design for failure and nothing fails,' ensuring recovery within the same Region without manual intervention.
KKey Concepts to Remember
- Auto Scaling Groups (ASGs) automatically adjust EC2 capacity.
- Spanning ASGs across multiple AZs provides high availability.
- ALBs distribute traffic across healthy instances in target groups.
- Multi-AZ deployments protect against single AZ failures.
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 (ASGs) automatically adjust EC2 capacity.
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 (ASGs) automatically adjust EC2 capacity., 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 (ASGs) automatically adjust EC2 capacity..
What is the correct answer to this question?
The correct answer is: Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets. — The correct answer is A because the current design has a single point of failure: all EC2 instances are in one Availability Zone (AZ-a). During an AZ impairment, those instances become unreachable, causing the checkout process to fail until the impairment ends or manual intervention occurs. By placing EC2 instances in an Auto Scaling Group spanning at least two AZs, the application can automatically recover by launching new instances in a healthy AZ, while the ALB distributes traffic across the surviving AZs. This minimizes operational overhead as Auto Scaling handles instance replacement automatically.
What should I do if I get this SAA-C03 question wrong?
Review auto Scaling Groups (ASGs) automatically adjust EC2 capacity., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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?
Auto Scaling Groups (ASGs) automatically adjust EC2 capacity.
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Last reviewed: Jun 11, 2026
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