SOA-C02 Cost and Performance Optimization Practice Question
A SysOps administrator notices that an Amazon RDS for MySQL instance has high read activity. The application performs many read queries but few writes. The database is currently a single db.r5.large instance. What change would improve read performance and reduce cost?
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
✓
Create a read replica and use a smaller instance type for the replica.
Creating a read replica offloads read traffic from the primary instance, improving performance for read-heavy workloads. Using a smaller instance type for the replica reduces cost compared to scaling up the primary. Option A is wrong because Multi-AZ provides high availability via a standby instance that cannot serve reads; it does not improve read performance. Option B (increasing instance size) is a vertical scaling approach that increases cost without the same cost-efficiency as a read replica. Option C is incorrect because migrating to DynamoDB would require application changes and may not be compatible with the existing MySQL schema and queries.
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 for high availability and use the standby for reads.
Why it's wrong here
Multi-AZ provides a synchronously replicated standby in a different Availability Zone for automatic failover, but Amazon RDS does not allow routing read traffic to the standby. The standby is a passive, non-accessible instance that only becomes active upon failover, so enabling Multi-AZ does not offload any read queries. Therefore, while Multi-AZ improves availability, it does not solve the read performance issue described.
- ✗
Increase the instance size to db.r5.xlarge.
Why it's wrong here
Scaling up the primary DB instance to a larger size like db.r5.xlarge would increase CPU and memory capacity, but the underlying problem is a read-heavy workload consuming resources. This approach simply adds more capacity to the same primary instance without distributing the read load, so queries still compete with writes for the same resources. Additionally, you would pay for the larger instance continuously, even though the replica approach could use a smaller, cost-effective instance for reads.
- ✗
Migrate the database to Amazon DynamoDB.
Why it's wrong here
Migrating a MySQL database to Amazon DynamoDB is a non-trivial change that requires redesigning the data model, rewriting application queries, and adapting to DynamoDB's key-value/document semantics. This is not a simple performance fix; it involves significant application changes, potential downtime, and migration risk. The question is about RDS read scaling, so a migration would alter the entire architecture rather than addressing the immediate read bottleneck.
- ✓
Create a read replica and use a smaller instance type for the replica.
Why this is correct
Creating a read replica allows you to offload read traffic to a separate, dedicated instance, freeing the primary to handle writes. You can specify a smaller instance type for the replica, such as a db.t3.medium, because read replicas do not need to match the primary's size; this reduces cost while still providing the read scaling needed. This directly addresses the read-heavy workload without migrating or overprovisioning the primary.
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Same concept, more angles
3 more ways 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 SysOps administrator manages an Amazon RDS for MySQL instance that experiences high CPU utilization during business hours. The application is read-heavy. Which action will most effectively improve performance and reduce cost?
medium- A.Enable Multi-AZ deployment.
- B.Scale up the instance size to a larger instance class.
- ✓ C.Add a read replica.
- D.Enable automated backups.
Why C: Adding a read replica offloads read traffic from the primary RDS for MySQL instance, directly addressing the read-heavy workload and high CPU utilization. This improves performance by distributing SELECT queries to the replica, and reduces cost because you can use a smaller primary instance and only pay for the replica's resources when needed, rather than scaling up the entire instance.
Variation 2. A SysOps administrator is troubleshooting high CPU utilization on an RDS for MySQL instance. The application is read-heavy. Which optimization technique would improve performance and potentially reduce costs?
hard- A.Delete unused indexes from the database.
- ✓ B.Implement RDS Read Replicas to offload read traffic.
- C.Increase the allocated storage size.
- D.Enable Multi-AZ deployment for failover support.
Why B: Implementing RDS Read Replicas offloads read traffic from the primary instance to one or more replicas, reducing CPU utilization on the primary. This improves performance for read-heavy applications and can also reduce costs because you can potentially use a smaller primary instance or fewer replicas than scaling up the primary. Read Replicas are asynchronous and can be in different AZs or regions.
Variation 3. An application uses an RDS MySQL DB instance. The administrator notices that read performance is poor during peak hours. What is a cost-effective way to improve read performance?
medium- A.Use Amazon ElastiCache for caching.
- B.Enable Multi-AZ deployment.
- C.Scale up the DB instance to a larger size.
- ✓ D.Create a read replica in the same region.
Why D: Creating a read replica offloads read traffic from the primary RDS instance, improving read performance during peak hours at a relatively low cost. Option A (ElastiCache) adds complexity and additional cost. Option B (Multi-AZ) is for high availability and disaster recovery, not for read performance. Option C (scaling up) addresses performance but is more expensive than adding a read replica.
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.