SOA-C02 Reserved Instances Practice Question
A company is using Amazon RDS for MySQL with Multi-AZ deployment. They want to optimize costs while maintaining high availability. Which TWO actions should the SysOps administrator take?
⚠ Common exam trap
SOA-C02 often tests the misconception that RDS supports compute auto scaling like EC2 Auto Scaling — candidates must remember RDS only auto-scales storage, not instance class.
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
✓
Purchase Reserved Instances for the database instance.
Option A is correct because purchasing Reserved Instances for the RDS DB instance provides a significant discount (up to ~69% for 3-year All Upfront terms) compared to On-Demand pricing, directly reducing cost while leaving the Multi-AZ high-availability configuration fully intact. Option D is correct because rightsizing the DB instance class (for example, moving from db.m5.xlarge to db.m5.large) eliminates spend on over-provisioned CPU/memory, and it can be done with a modification that preserves the Multi-AZ standby, so high availability is maintained. Option B is wrong because removing Multi-AZ sacrifices the synchronous standby replica and automatic failover, violating the requirement to maintain high availability. Option C is wrong because RDS does not support auto scaling of the DB instance itself; only storage can be auto scaled, and read scaling requires Read Replicas, not instance auto scaling. Option E is wrong because a Single-AZ deployment plus snapshots is not highly available—snapshot restore creates a new instance and involves substantial RPO/RTO, so it fails the availability requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Purchase Reserved Instances for the database instance.
Why this is correct
Purchasing Reserved Instances for the RDS instance is a cost-optimization practice that does not affect the deployment architecture. Reserved Instances provide a significant hourly discount in exchange for a one- or three-year commitment, applied to the compute portion of the DB instance, while Multi-AZ and its automatic failover capability remain fully intact. This directly reduces operational costs without compromising high availability, making it a correct choice.
- ✗
Remove Multi-AZ to reduce costs.
Why it's wrong here
Removing Multi-AZ reduces costs by eliminating the standby replica and its associated compute, storage, and I/O overhead, but it also removes automatic failover. In the event of a primary database failure or an Availability Zone outage, the instance remains unavailable until you manually restore from a snapshot or launch a new instance, resulting in significant downtime. Since the requirement is to maintain high availability, this option is unacceptable.
- ✗
Enable auto scaling for the RDS instance to handle variable load.
Why it's wrong here
Amazon RDS does not support automatic scaling of compute resources (CPU/memory) based on load; only storage can auto-scale, and that only increases allocated storage. You would need to manually modify the DB instance class, which may cause downtime or a failover and does not provide the elastic compute adjustment you need. Therefore, this is not a valid cost-optimization action and would not help handle variable load.
- ✓
Review the instance size and downsize if it is over-provisioned.
Why this is correct
Right-sizing the DB instance is a valid cost-optimization strategy: by monitoring CloudWatch metrics such as CPUUtilization, FreeableMemory, and DatabaseConnections, you can determine whether the current instance class is over-provisioned. If consistent low utilization is observed, you can modify the instance to a smaller class, reducing compute costs while keeping Multi-AZ enabled and preserving high availability. This approach does not compromise fault tolerance and is therefore correct.
- ✗
Move to a single-AZ deployment and take snapshots for recovery.
Why it's wrong here
Moving to a single-AZ deployment removes the synchronous standby replica that Multi-AZ provides, eliminating automatic failover during an AZ outage or DB health event. Snapshots, while useful for backup and point-in-time recovery, require manual restoration and can incur data loss equal to the time since the last snapshot, plus minutes or hours of recovery downtime. This approach sacrifices the required high availability and introduces unacceptable recovery time.
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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.