- A
Set the ECS deployment configuration to maximum percent 100 so tasks replace instances faster during rollouts.
Why wrong: Deployment timing can help during releases but does not ensure capacity exists in another AZ during failures.
- B
Increase ASG min size to at least 2 and ensure the ASG uses subnets in at least two Availability Zones.
Multi-AZ instance capacity ensures tasks have eligible compute in another AZ when one AZ loses instances.
- C
Enable ALB connection draining longer than expected so existing connections survive longer during an AZ event.
Why wrong: Connection draining affects in-flight sessions but does not restore capacity for new requests after AZ loss.
- D
Reduce task memory reservations to pack both tasks onto a single EC2 instance.
Why wrong: Packing tasks onto fewer instances increases blast radius; it does not improve multi-AZ resilience.
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.
An ECS service runs on EC2 instances and is fronted by an ALB. The ALB spans two Availability Zones, and the ECS service desired count is 2 tasks. The underlying EC2 capacity uses an Auto Scaling group (ASG) with min size set to 1, and the ASG also spans only one subnet in practice. What is the most effective change to meet the requirement that the service continues during a single-AZ instance loss?
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
Increase ASG min size to at least 2 and ensure the ASG uses subnets in at least two Availability Zones.
The current architecture has a single point of failure because the Auto Scaling group (ASG) spans only one subnet (one Availability Zone). If that AZ fails, all EC2 instances are lost, and the ECS service cannot run any tasks. Increasing the ASG min size to at least 2 and configuring it to use subnets in at least two AZs ensures that EC2 instances are distributed across AZs, allowing the ECS service to maintain at least one task in the surviving AZ during a single-AZ failure.
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.
- ✗
Set the ECS deployment configuration to maximum percent 100 so tasks replace instances faster during rollouts.
Why it's wrong here
Deployment timing can help during releases but does not ensure capacity exists in another AZ during failures.
- ✓
Increase ASG min size to at least 2 and ensure the ASG uses subnets in at least two Availability Zones.
Why this is correct
Multi-AZ instance capacity ensures tasks have eligible compute in another AZ when one AZ loses instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable ALB connection draining longer than expected so existing connections survive longer during an AZ event.
Why it's wrong here
Connection draining affects in-flight sessions but does not restore capacity for new requests after AZ loss.
- ✗
Reduce task memory reservations to pack both tasks onto a single EC2 instance.
Why it's wrong here
Packing tasks onto fewer instances increases blast radius; it does not improve multi-AZ resilience.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on ECS-specific settings (like deployment configuration or task placement) rather than recognizing that the root cause is the ASG's single-AZ limitation, which is a fundamental infrastructure resilience issue.
Detailed technical explanation
How to think about this question
Under the hood, the ECS scheduler places tasks based on the available EC2 instances in the cluster, which are launched by the ASG. If the ASG is confined to one AZ, the cluster's capacity is limited to that AZ's resources. By configuring the ASG to span multiple AZs and setting a min size of at least 2, the ASG will maintain at least one EC2 instance in each AZ (assuming a balanced distribution), ensuring that the ECS service's desired count of 2 tasks can be spread across AZs. This aligns with the AWS Well-Architected Framework's principle of deploying across multiple AZs for high availability.
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
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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: Increase ASG min size to at least 2 and ensure the ASG uses subnets in at least two Availability Zones. — The current architecture has a single point of failure because the Auto Scaling group (ASG) spans only one subnet (one Availability Zone). If that AZ fails, all EC2 instances are lost, and the ECS service cannot run any tasks. Increasing the ASG min size to at least 2 and configuring it to use subnets in at least two AZs ensures that EC2 instances are distributed across AZs, allowing the ECS service to maintain at least one task in the surviving AZ during a single-AZ failure.
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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