- A
Enable Multi-AZ for the RDS instance and scale up the instance size
Why wrong: Multi-AZ provides high availability, not read scaling. The standby is not used for reads. Scaling up increases cost without addressing the root cause (read-heavy workload) and may provide limited improvement.
- B
Implement a read replica for the RDS instance and modify the application to route read queries to the read replica
Read replicas can handle read traffic, reducing load on the primary instance. This improves performance and, by avoiding unnecessary scale-up, can be more cost-effective. Only the primary instance needs to be sized for writes.
- C
Enable Amazon RDS Performance Insights and increase the storage allocation
Why wrong: Performance Insights helps identify performance bottlenecks but does not directly reduce CPU load. Increasing storage may improve I/O performance if bottlenecks are I/O-related, but it does not address high CPU from read queries and increases cost.
- D
Implement Amazon ElastiCache for Memcached in front of the database and migrate read-heavy queries to cache
Why wrong: ElastiCache can improve performance by caching frequent reads, but it adds additional cost and operational overhead. For a workload where 90% of queries are reads, read replicas are a simpler and often more cost-effective solution, especially if the data is not highly cacheable or frequently updated.
SOA-C02 Cost and Performance Optimization Practice Question
This SOA-C02 practice question tests your understanding of cost and performance optimization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application reads data from an Amazon RDS for MySQL database. During peak hours, the database CPU utilization is consistently high, and the application experiences increased latency. The SysOps administrator observes that 90% of database queries are read-only. Which combination of actions will both improve performance and optimize costs?
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
Implement a read replica for the RDS instance and modify the application to route read queries to the read replica
Option B is correct because implementing a read replica offloads read-heavy (90%) queries from the primary RDS instance, reducing CPU utilization and latency. Modifying the application to route read queries to the replica distributes the workload, improving performance while avoiding costly vertical scaling. This optimizes costs by using a smaller primary instance and paying only for the replica's resources.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 the RDS instance and scale up the instance size
Why it's wrong here
Multi-AZ provides high availability, not read scaling. The standby is not used for reads. Scaling up increases cost without addressing the root cause (read-heavy workload) and may provide limited improvement.
- ✓
Implement a read replica for the RDS instance and modify the application to route read queries to the read replica
Why this is correct
Read replicas can handle read traffic, reducing load on the primary instance. This improves performance and, by avoiding unnecessary scale-up, can be more cost-effective. Only the primary instance needs to be sized for writes.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable Amazon RDS Performance Insights and increase the storage allocation
Why it's wrong here
Performance Insights helps identify performance bottlenecks but does not directly reduce CPU load. Increasing storage may improve I/O performance if bottlenecks are I/O-related, but it does not address high CPU from read queries and increases cost.
- ✗
Implement Amazon ElastiCache for Memcached in front of the database and migrate read-heavy queries to cache
Why it's wrong here
ElastiCache can improve performance by caching frequent reads, but it adds additional cost and operational overhead. For a workload where 90% of queries are reads, read replicas are a simpler and often more cost-effective solution, especially if the data is not highly cacheable or frequently updated.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Multi-AZ (high availability) with read replicas (performance scaling), or assume caching (ElastiCache) is always the best choice for read-heavy workloads without considering the simplicity and cost-effectiveness of read replicas for database-level offloading.
Detailed technical explanation
How to think about this question
Amazon RDS read replicas use asynchronous replication from the primary instance to one or more read-only replicas, which can be promoted to a primary in a disaster. The application must be configured to use a separate endpoint for read queries, often via a database connection pool or ORM that supports read/write splitting. In real-world scenarios, read replicas can also be used for reporting or analytics without impacting production performance.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Cost and Performance Optimization — This question tests Cost and Performance Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement a read replica for the RDS instance and modify the application to route read queries to the read replica — Option B is correct because implementing a read replica offloads read-heavy (90%) queries from the primary RDS instance, reducing CPU utilization and latency. Modifying the application to route read queries to the replica distributes the workload, improving performance while avoiding costly vertical scaling. This optimizes costs by using a smaller primary instance and paying only for the replica's resources.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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