- 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. 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?
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.
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.
When this WOULD be correct
If the question described an RDS failure causing downtime while EC2 instances were healthy and distributed across AZs, then switching from Single-AZ to Multi-AZ would be the correct fix to ensure database high availability.
- ✗
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.
When this WOULD be correct
If the question described a scenario where transient traffic spikes cause false health check failures and the goal is to reduce unnecessary instance replacements while maintaining single-AZ deployment, increasing health check thresholds would be appropriate.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Move the EC2 instances into Auto Scaling Groups that span private subnets in at least two AZs, keeping the ALB spanning those subnets.Correct answer▾
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.
✗Switch from RDS Single-AZ to RDS Multi-AZ, keeping the EC2 instances in only AZ-a because failover will still reach them.Wrong answer — click to see why▾
Why this is wrong here
The RDS Multi-AZ failover does not address the root cause: EC2 instances are only in AZ-a, so if that AZ fails, no healthy instances remain to serve traffic, causing checkout to fail until new instances are provisioned.
★ When this WOULD be the correct answer
If the question described an RDS failure causing downtime while EC2 instances were healthy and distributed across AZs, then switching from Single-AZ to Multi-AZ would be the correct fix to ensure database high availability.
Why candidates choose this
Candidates see 'Multi-AZ' and assume it solves all availability issues, overlooking that the compute layer (EC2) is still single-AZ and becomes the bottleneck during an AZ impairment.
✗Terminate the ALB and use a Network Load Balancer (NLB) in front of the existing single-AZ EC2 instances.Wrong answer — click to see why▾
Why this is wrong here
The NLB does not solve the single-AZ EC2 instance issue; if AZ-a fails, all instances are lost regardless of load balancer type. The ALB already spans multiple AZs, so replacing it with an NLB adds no benefit for multi-AZ recovery.
★ When this WOULD be the correct answer
When the application requires static IP addresses for whitelisting or is latency-sensitive and uses UDP/TCP protocols that ALB does not support, and the instances are already in multiple AZs or the question specifies that AZ failure is not the concern.
Why candidates choose this
Candidates may think NLB is inherently more resilient or faster for failover, or they confuse the load balancer type with the need for multi-AZ instance placement.
✗Add more EC2 instances in AZ-a and increase the ALB health check thresholds to avoid unnecessary replacements during impairments.Wrong answer — click to see why▾
Why this is wrong here
Adding more EC2 instances in a single AZ does not provide fault tolerance across AZs; during an AZ impairment, all instances in AZ-a become unavailable, causing checkout delays. Increasing health check thresholds only delays failure detection, not recovery.
★ When this WOULD be the correct answer
If the question described a scenario where transient traffic spikes cause false health check failures and the goal is to reduce unnecessary instance replacements while maintaining single-AZ deployment, increasing health check thresholds would be appropriate.
Why candidates choose this
Candidates may think that adding more instances in the same AZ provides redundancy and that higher health check thresholds prevent premature replacements, overlooking that the real issue is AZ-level failure, not instance-level health.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
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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.
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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