SAA-C03 Design High-Performing Architectures Practice Question
A retail company runs a stateless web tier on Amazon EC2 instances behind an Application Load Balancer. Traffic is steady during the day but drops to near zero between 01:00 and 06:00, and the team wants to reduce cost without manual intervention. The instances take about four minutes to boot and warm up. Which configuration meets these requirements?
⚠ Common exam trap
The trap here is choosing a metric-driven policy for a workload whose demand is already known by clock time, so the group reacts late instead of scaling ahead of the pattern.
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
✓
Create a scheduled scaling action that reduces the Auto Scaling group's desired capacity at 01:00 and increases it at 06:00.
Scheduled scaling is the right fit when capacity needs follow a known timetable: it changes desired capacity at 01:00 and 06:00 regardless of metric lag, so the group shrinks during the predictable trough and is already expanding before morning traffic arrives. Reactive policies such as target tracking or step scaling would respond only after metrics move, which conflicts with the fixed daily pattern and the four-minute warm-up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable an Application Load Balancer idle timeout and let the load balancer stop idle targets automatically.
Why it's wrong here
An ALB idle timeout closes idle connections; it does not terminate or stop EC2 instances and has no effect on Auto Scaling capacity. The instances would continue running and billing through the night, so the cost goal is not met, and the setting can even disrupt long-lived client connections during the day.
- ✗
Attach a step scaling policy that removes instances when the ALB request count per target falls below a threshold.
Why it's wrong here
Step scaling also responds to CloudWatch alarms after the fact, so it cannot anticipate the 01:00 drop or the 06:00 recovery. The four-minute boot time means the group would be under-provisioned when morning traffic arrives, and the policy adds alarm configuration complexity without exploiting the fact that the trough is predictable by time of day.
- ✗
Configure a target tracking scaling policy based on average CPU utilization with a target of 50 percent.
Why it's wrong here
Target tracking reacts to observed metrics, so it scales in only after utilization has already fallen and scales out only after traffic returns. With a four-minute warm-up, the morning ramp would begin with too few instances, and the overnight trough would still keep instances running until the metric drop is detected, which does not match a known, clock-based traffic pattern.
- ✓
Create a scheduled scaling action that reduces the Auto Scaling group's desired capacity at 01:00 and increases it at 06:00.
Why this is correct
Scheduled scaling changes desired capacity at known times, which matches a workload with a predictable daily trough. Because the team knows exactly when traffic falls and rises, a schedule avoids the lag of reactive policies and removes the need for manual changes, while the warm-up time is handled by starting the increase slightly before 06:00.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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