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Question 860 of 1,040

Design Resilient Architectures →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets. This directly resolves the recovery delay during an AZ impairment because the current single-AZ design creates a single point of failure for compute capacity; when that AZ is impaired, all EC2 instances are lost, forcing the application to wait for the impairment to end or for manual intervention. By distributing EC2 instances across multiple AZs with Auto Scaling, the ALB’s health checks automatically route traffic to healthy instances in the surviving AZ, enabling near-instantaneous recovery within the same Region. On the SAA-C03 exam, this scenario tests your understanding of high availability design patterns and the trap of assuming Multi-AZ RDS alone guarantees full recovery—the compute layer must also be resilient. A common memory tip is “compute and data must both span AZs; don’t let your EC2 be a single point of failure.”

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.

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.

Question 1mediummultiple choice

Review the full subnetting walkthrough →

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.

Full breakdown with real-world context →

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 current design places EC2 instances only in AZ-a, so when that AZ becomes impaired, all compute capacity is lost, causing checkout to fail until the impairment ends or manual intervention occurs. By moving EC2 instances into Auto Scaling Groups spanning at least two AZs, the application gains automatic recovery within the same Region because the ALB can route traffic to healthy instances in the remaining AZs. This change minimizes operational overhead because Auto Scaling automatically replaces failed instances and maintains desired capacity across AZs, while the ALB’s health checks ensure traffic is only sent to healthy targets.

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.

✓
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
Read the scenario before looking for a memorised answer.
✗
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 assume Multi-AZ RDS alone guarantees full application resilience, overlooking that the compute layer (EC2) must also be distributed across AZs to survive an AZ impairment.

Detailed technical explanation

How to think about this question

Under the hood, an ALB distributes traffic across targets in multiple AZs using cross-zone load balancing, which is enabled by default. When an AZ becomes impaired, the ALB’s health checks (HTTP/HTTPS or TCP) mark instances in that AZ as unhealthy, and traffic is redirected to healthy instances in other AZs. Auto Scaling Groups with a multi-AZ strategy use Amazon EC2 Auto Scaling to automatically launch replacement instances in the remaining AZs, leveraging the group’s capacity rebalancing feature to maintain the desired instance count across AZs. In a real-world scenario, this design ensures that even if an entire AZ fails, the application can continue serving traffic within seconds to minutes, depending on health check intervals and instance launch times.

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.

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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: Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets. — The current design places EC2 instances only in AZ-a, so when that AZ becomes impaired, all compute capacity is lost, causing checkout to fail until the impairment ends or manual intervention occurs. By moving EC2 instances into Auto Scaling Groups spanning at least two AZs, the application gains automatic recovery within the same Region because the ALB can route traffic to healthy instances in the remaining AZs. This change minimizes operational overhead because Auto Scaling automatically replaces failed instances and maintains desired capacity across AZs, while the ALB’s health checks ensure traffic is only sent to healthy targets.

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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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 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?

medium

✓ A.Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.
B.Switch from RDS Single-AZ to RDS Multi-AZ, keeping the EC2 instances in only AZ-a because failover will still reach them.
C.Terminate the ALB and use a Network Load Balancer (NLB) in front of the existing single-AZ EC2 instances.
D.Add more EC2 instances in AZ-a and increase the ALB health check thresholds to avoid unnecessary replacements during impairments.

Why A: 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.

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