← SAA-C03·Amazon Web Services

Question 635 of 1,040

Design Resilient Architectures →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is to place the Auto Scaling group across multiple Availability Zones by configuring it with subnets in at least two AZs. This directly eliminates the single point of failure because a Multi-AZ Auto Scaling group for AZ resilience ensures that if one AZ goes down, the remaining AZs continue running instances to handle traffic. The Application Load Balancer is already set up for multi-AZ, but the ASG’s single-AZ subnet placement is the bottleneck—this is a classic SAA-C03 trap where candidates focus on the ALB and forget the ASG must also span AZs. The exam tests your understanding that resilience requires both the load balancer and the compute layer to be distributed. A simple memory tip: “ALB spans AZs, so must your ASG—don’t let one subnet sink your app.”

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 web application runs on an Amazon EC2 Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The ALB is configured to use at least two Availability Zones (AZs), but the ASG currently uses subnets in only one AZ. If that AZ becomes unavailable, the application stops serving requests. Which change most directly improves resilience to an AZ outage?

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.

Question 1easymultiple choice

Review the full subnetting walkthrough →

A
Keep the ASG in one Availability Zone, but reduce ALB health check intervals.
Why wrong: Reducing health check intervals only changes how quickly the ALB marks targets unhealthy. It does not create capacity in other AZs, so the ALB still has no healthy instances to route to when the only ASG AZ fails.
B
Place the ASG across multiple Availability Zones by configuring it with subnets in at least two AZs.
An ASG launches instances into the AZs of the subnets you specify. By placing the ASG in at least two AZs, the ALB can route traffic to healthy targets in the remaining AZ(s) if one AZ fails, enabling recovery as new instances maintain desired capacity.
C
Switch the load balancer from an ALB to an NLB to remove HTTP health check dependency.
Why wrong: Changing from ALB to NLB does not address the root cause: there is no instance capacity in other AZs. Without multi-AZ compute capacity, any load balancer cannot serve traffic during the AZ outage.
D
Add an Amazon SQS queue to buffer requests during failures.
Why wrong: A queue can help with asynchronous work, but a typical web request/response path still requires immediate compute capacity to accept and handle requests. Queueing does not eliminate the loss of in-AZ instances when the only ASG AZ fails.

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

✓

Place the ASG across multiple Availability Zones by configuring it with subnets in at least two AZs.

Option B is correct because distributing an Auto Scaling group across multiple Availability Zones (AZs) ensures that if one AZ fails, the remaining AZs continue to serve traffic. The Application Load Balancer (ALB) is already configured for at least two AZs, but the ASG’s single-AZ subnet placement creates a single point of failure. By adding subnets in at least two AZs to the ASG, the application becomes resilient to an AZ outage without any other architectural changes.

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.

✗
Keep the ASG in one Availability Zone, but reduce ALB health check intervals.
Why it's wrong here
Reducing health check intervals only changes how quickly the ALB marks targets unhealthy. It does not create capacity in other AZs, so the ALB still has no healthy instances to route to when the only ASG AZ fails.
✓
Place the ASG across multiple Availability Zones by configuring it with subnets in at least two AZs.
Why this is correct
An ASG launches instances into the AZs of the subnets you specify. By placing the ASG in at least two AZs, the ALB can route traffic to healthy targets in the remaining AZ(s) if one AZ fails, enabling recovery as new instances maintain desired capacity.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Switch the load balancer from an ALB to an NLB to remove HTTP health check dependency.
Why it's wrong here
Changing from ALB to NLB does not address the root cause: there is no instance capacity in other AZs. Without multi-AZ compute capacity, any load balancer cannot serve traffic during the AZ outage.
✗
Add an Amazon SQS queue to buffer requests during failures.
Why it's wrong here
A queue can help with asynchronous work, but a typical web request/response path still requires immediate compute capacity to accept and handle requests. Queueing does not eliminate the loss of in-AZ instances when the only ASG AZ fails.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume the ALB’s multi-AZ configuration automatically protects the application, overlooking that the ASG must also span multiple AZs to provide compute redundancy.

Detailed technical explanation

How to think about this question

Under the hood, an Auto Scaling group defines a list of subnets (one per AZ) and launches instances evenly across them by default. The ALB’s cross-zone load balancing distributes traffic to healthy instances in any AZ, but if the ASG has subnets in only one AZ, the ALB’s target group will have no registered instances when that AZ fails. In a real-world scenario, this design is common when developers mistakenly assume the ALB’s multi-AZ configuration alone provides resilience, ignoring that the compute layer must also be multi-AZ.

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: Place the ASG across multiple Availability Zones by configuring it with subnets in at least two AZs. — Option B is correct because distributing an Auto Scaling group across multiple Availability Zones (AZs) ensures that if one AZ fails, the remaining AZs continue to serve traffic. The Application Load Balancer (ALB) is already configured for at least two AZs, but the ASG’s single-AZ subnet placement creates a single point of failure. By adding subnets in at least two AZs to the ASG, the application becomes resilient to an AZ outage without any other architectural changes.

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.

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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. 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?

easy

A.Increase the desired capacity in the existing Availability Zone to handle all traffic during an outage.
✓ B.Deploy the ALB and the Auto Scaling group across at least two Availability Zones so healthy targets remain.
C.Enable longer ALB health check intervals so failing instances are detected more slowly.
D.Switch from the ALB to an Internet Gateway so instances can fail over to the public internet.

Why B: 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.

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