SOA-C02 Cost and Performance Optimization Practice Question
A company is running a web application on a fleet of EC2 instances behind an Application Load Balancer. The application experiences variable traffic patterns with predictable spikes every day at 2 PM. The company wants to optimize costs while maintaining performance. Which solution is MOST cost-effective?
⚠ Common exam trap
SOA-C02 often tests the difference between reactive and proactive scaling; candidates may choose dynamic scaling because it is more commonly discussed, but for predictable spikes, scheduled scaling is the most cost-effective.
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
✓
Use scheduled scaling to add instances before the spike and remove them after.
Scheduled scaling is the correct answer because the traffic spikes are predictable and occur at a known time (2 PM daily). Scheduled scaling allows you to define a schedule (using cron expressions) to automatically increase the desired capacity of the Auto Scaling group before the spike and decrease it afterward, ensuring performance while minimizing costs during off-peak hours. This is more cost-effective than manual scaling because it eliminates the need for human intervention and ensures instances are only running when needed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use manual scaling by adjusting the desired capacity each day at 2 PM.
Why it's wrong here
Manual scaling by adjusting desired capacity each day at 2 PM is operationally risky and inefficient. It requires a human to remember to change the Auto Scaling group's desired count exactly on time, and the adjustment is applied at the spike time, not before, so instances may still be initializing when traffic arrives. If the engineer forgets to remove the extra capacity after the spike, the company pays for unused instances indefinitely. There is no integration with CloudWatch, lifecycle hooks, or health checks, and this approach is not automated, making it fragile for production workloads.
- ✗
Purchase Reserved Instances for the entire fleet to reduce costs.
Why it's wrong here
Purchasing Reserved Instances for the entire fleet is a cost-optimization measure, not a scaling mechanism—it changes only the billing rate for instance usage, not the number of running instances. Because a daily spike is predictable and temporary, committing to a 1- or 3-year Reserved Instance for all instances would lock you into paying for capacity that is idle outside the spike window, increasing overall cost. Reserved Instances would only make sense for a steady-state baseline fleet, not for handling ephemeral bursts in traffic.
- ✓
Use scheduled scaling to add instances before the spike and remove them after.
Why this is correct
Scheduled scaling is the correct approach for a predictable, recurring daily spike because it allows you to add capacity in advance and remove it afterward based on a schedule, without any manual intervention. You can configure the Auto Scaling group to increase the desired capacity at, for example, 1:30 PM to give new instances time to enter the InService state and start receiving traffic before the 2 PM spike, then decrease it at 4 PM to terminate unneeded instances. This directly balances performance and cost, and it integrates with CloudWatch metrics and ELB health checks to ensure the added instances are truly ready. It is the idiomatic AWS solution for traffic patterns that repeat on a known timetable.
- ✗
Use dynamic scaling policies based on CPU utilization.
Why it's wrong here
Dynamic scaling policies based on CPU utilization react to real-time conditions, which means they detect the spike only after CPU has already risen, then often take 2–5 minutes or more to launch and warm up new instances, causing a performance lag during the actual spike. In a sharply spiking web workload, this reactive approach may fail to keep up and can trigger a continuous loop of scaling in and out, known as flapping, unless you carefully tune cooldowns and thresholds. Furthermore, CPU utilization alone may not reflect true application demand if the workload is network- or memory-bound, so the metric could be an inaccurate signal for when to scale.
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Same concept, more angles
1 more way this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is running a production web application on EC2 instances behind an ALB. The application experiences predictable traffic spikes during business hours. Which cost optimization strategy would be MOST effective?
medium- ✓ A.Configure Scheduled Scaling to add instances before the spike and remove after.
- B.Use Spot Instances for the entire workload.
- C.Use larger instance types to handle the spikes without scaling.
- D.Use On-Demand instances exclusively to handle the spikes.
Why A: The most effective cost optimization strategy because Scheduled Scaling allows you to increase capacity predictably before traffic spikes and decrease afterward, ensuring you only pay for what you need. Option B is incorrect because Spot Instances can be interrupted and are not suitable for production workloads that require high availability. Option C is incorrect because using larger instances does not dynamically adjust to spikes and may lead to over-provisioning during low traffic. Option D is incorrect because On-Demand instances are more expensive than using scheduled scaling with a mix of Reserved Instances or Savings Plans to cover the baseline and scheduled scaling for the spikes.
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 SOA-C02 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 SOA-C02 exam.