SAA-C03 Design Cost-Optimized Architectures Practice Question
A small analytics team runs a nightly batch job on a single Amazon EC2 instance. The job starts at 2:00 AM and finishes by 4:00 AM. The instance is idle for the rest of the day. The team wants to reduce EC2 costs and is willing to accept that the instance may be stopped and started. Which action will reduce costs MOST effectively?
⚠ Common exam trap
The trap here is assuming that a Reserved Instance or a larger instance type will reduce cost, when the biggest saving comes from not paying for the instance at all during the long idle period.
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
✓
Stop the instance when the job completes and start it again before the next run using an automated schedule.
When an instance is needed only for a short, predictable window, stopping it during idle hours removes the compute charges for those hours. Automated start and stop scheduling is a simple and effective cost optimization for intermittent workloads. Reserved Instances and larger instance types do not eliminate the cost of idle time.
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 job to a larger instance type to finish faster.
Why it's wrong here
A larger instance may complete the job faster, but it also costs more per hour. If the job is not compute-bound or the runtime is dominated by I/O or external dependencies, the savings may be negligible. More importantly, a larger instance does not address the core issue of paying for 22 hours of idle time each day.
- ✗
Enable detailed monitoring and create a CloudWatch alarm to reboot the instance if CPU utilization is low.
Why it's wrong here
Rebooting an instance does not reduce cost, and low CPU utilization does not mean the instance should be rebooted. This action adds monitoring cost and may disrupt the batch job. It does not stop the instance during idle hours, so it fails to reduce the compute charges that dominate the bill.
- ✓
Stop the instance when the job completes and start it again before the next run using an automated schedule.
Why this is correct
Stopping an instance when it is not needed means you do not pay for compute hours while it is idle. Since the job runs for only about two hours each night, stopping the instance for the remaining 22 hours drastically reduces cost. Automated start and stop can be implemented with instance scheduler solutions or EventBridge and Lambda.
- ✗
Purchase a 1-year All Upfront Reserved Instance for the instance.
Why it's wrong here
A Reserved Instance provides a discount on the hourly rate but still charges for the full commitment period, whether or not the instance is running. Since the instance is idle most of the day, the discount does not eliminate the cost of idle hours. Stopping the instance would save more than a reservation in this case.
Go deeper
Related to this question
About these practice questions
This SAA-C03 question is part of Courseiva's 935-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
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
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.