SAA-C03 Auto Scaling Group (ASG) minimum size Practice Question
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?
⚠ Common exam trap
The trap here is that candidates may focus on the ALB's multi-AZ configuration and overlook that the compute layer (ASG/EC2) is the actual bottleneck, leading them to choose connection draining or deployment settings that do not address the fundamental lack of cross-AZ capacity.
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: the ASG spans only one subnet (one AZ), so if that AZ fails, all EC2 instances are lost, and the ECS service cannot run any tasks. By increasing the ASG min size to at least 2 and ensuring it uses subnets in at least two AZs, the ASG will maintain at least one healthy instance in each AZ, allowing the ECS service to survive a single-AZ outage. This aligns with the AWS Well-Architected Framework's principle of deploying across multiple AZs for high availability.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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