SOA-C02 Cost and Performance Optimization Practice Question
A SysOps administrator needs to reduce costs for an Amazon RDS for MySQL DB instance that is used for development. The instance is only needed during business hours (9 AM to 5 PM) on weekdays. Which solution is the MOST cost-effective while maintaining the ability to start and stop the instance on a schedule?
⚠ Common exam trap
Watch out — candidates often choose a Lambda function (Option C) thinking it is the most flexible, but they overlook that AWS Instance Scheduler is a pre-built, managed solution that reduces operational overhead and is the recommended pattern for scheduled start/stop of RDS instances in the AWS Well-Architected Framework.
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 AWS Instance Scheduler to stop and start the RDS instance on a schedule.
AWS Instance Scheduler is a fully managed solution designed specifically to start and stop RDS instances on a defined schedule, such as weekdays from 9 AM to 5 PM. This eliminates compute costs during non-business hours while preserving the instance's storage and configuration, making it the most cost-effective and reliable approach for a development environment.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a read replica and promote it when needed.
Why it's wrong here
A read replica is a separate database instance that incurs its own compute, storage, and I/O charges; promoting it does not automatically decommission the original primary. To actually save money, you would need to manually delete the original after promotion, which is a failover operation, not a recurring schedule-based cost control. This strategy does not match the requirement to reduce compute costs during non-business hours.
- ✗
Purchase a reserved instance for the DB instance.
Why it's wrong here
Reserved Instances provide a discounted hourly rate in exchange for a 1- or 3-year commitment and bill continuously at that rate for every hour of the term. Even if the database is stopped each evening, you still pay for the reserved hours across the entire month. This payment model is designed for steady-state workloads, not for a database that is only used during business hours, so it would not eliminate or reduce charges for the idle overnight periods.
- ✗
Use a Lambda function to stop the instance at 5 PM and start it at 9 AM on weekdays.
Why it's wrong here
An AWS Lambda function itself does not have a built-in scheduler; you must configure Amazon EventBridge (CloudWatch Events) rules to invoke it on a cron expression at the desired times. The option as written leaves out that required scheduling mechanism, making it incomplete. Even with correct permissions, RDS instances can only remain stopped for up to seven days before AWS automatically restarts them, so longer holiday shutdowns would also be problematic.
- ✓
Use AWS Instance Scheduler to stop and start the RDS instance on a schedule.
Why this is correct
AWS Instance Scheduler is a purpose-built solution that uses a CloudFormation stack and tags to automatically start and stop RDS instances on a defined schedule. It leverages Lambda functions and an Amazon DynamoDB state table to track and apply the schedule without requiring you to build a custom scheduler. This reduces compute charges during off hours while storage and backup costs continue, precisely matching the requirement for a business-hours-only database.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
Related to this question
About these practice questions
Courseiva writes every SOA-C02 question from scratch — 1,169 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.