SOA-C02 Cost and Performance Optimization Practice Question
A company wants to reduce costs for their Amazon RDS for PostgreSQL database. Which TWO actions would help achieve this?
⚠ Common exam trap
SOA-C02 often tests the misconception that features like Multi-AZ or deletion protection reduce costs, when they actually increase cost or have no cost impact.
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 database instance during non-business hours.
Option B is correct because stopping an RDS for PostgreSQL instance during non-business hours eliminates instance-hour charges while it is stopped (storage charges still apply), directly reducing compute costs for a database that is not needed around the clock. Option E is correct because purchasing a Reserved Instance for the DB instance provides a significant discount (up to roughly 69% versus On-Demand for a 3-year, all-upfront term) in exchange for a commitment to a specific instance family and Region, lowering the effective hourly rate for steady-state workloads. Option A is not cost-reducing because Multi-AZ runs a synchronous standby replica in a second AZ, roughly doubling instance and storage cost in exchange for high availability. Option C is a safety control that prevents accidental deletion and has no positive effect on cost. Option D increases cost, since extending backup retention to 35 days keeps more automated backup storage beyond the free allocation and incurs additional backup storage charges.
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 Multi-AZ deployment for high availability.
Why it's wrong here
Enabling Multi-AZ deploys a synchronous standby instance in a separate Availability Zone, so AWS bills you for both the primary and standby compute capacity plus double the provisioned storage and I/O. While this improves durability and provides automatic failover, it roughly doubles database infrastructure costs and is therefore a cost-reduction detractor, not a savings strategy.
- ✓
Stop the database instance during non-business hours.
Why this is correct
Stopping the RDS DB instance during non-business hours places it in a 'stopped' state (you can stop it for up to 7 days at a time), during which compute and I/O charges are no longer incurred. Storage and backup costs continue, but you effectively eliminate the expensive instance-hour component for test and development environments that are only used in business hours. This delivers direct cost savings and is the correct answer here.
- ✗
Enable deletion protection to prevent accidental deletion.
Why it's wrong here
Deletion protection is an administrative guardrail that prevents a DB instance from being deleted accidentally via the console or API; it has no effect on the instance's hourly compute, storage, backup, or data transfer billing. You cannot save money by enabling it because it simply toggles the 'DeletionProtection' attribute and does not alter resource provisioning or utilization. It is a useful safety feature, but it is not a cost-reduction mechanism.
- ✗
Increase the backup retention period to 35 days.
Why it's wrong here
Extending the backup retention period from 7 to 35 days means Amazon RDS stores more automated snapshots, which increases the total backup storage billed per GB-month. Each backup is stored in S3 and billed at the regional backup storage rate, so a longer retention window directly raises storage costs rather than lowering them. While this increases durability and point-in-time recovery capability, it works against a cost-saving goal.
- ✓
Purchase a Reserved Instance for the database instance.
Why this is correct
Purchasing a Reserved Instance for the RDS database commits you to an upfront or monthly payment for a 1-year or 3-year term, and in exchange AWS applies a significantly lower hourly rate to that instance compared with On-Demand pricing. This reduces the compute portion of the bill by 30–70 percent depending on term and payment option, making it a legitimate strategy to lower ongoing costs for a consistently running database. Just ensure the instance class and engine match what you actually run.
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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
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.