- A
Implement ElastiCache Redis cluster to cache query results and reduce DB load.
Why wrong: Caching adds complexity and cost; for this scenario, a read replica directly addresses the DB CPU spike.
- B
Enable RDS Performance Insights and create a CloudWatch alarm to reboot the DB instance on high CPU.
Why wrong: Rebooting does not resolve the root cause of high CPU and causes downtime.
- C
Add an RDS read replica in the same region and configure the application to route read queries to the replica.
A read replica offloads read traffic, reducing CPU on the primary, and is cost-effective for read-heavy workloads.
- D
Switch the DB instance to a larger instance type to handle the load.
Why wrong: Scaling up increases cost; the workload is read-heavy, so a read replica is more cost-effective.
Quick Answer
The answer is to add an RDS read replica in the same region and route read queries to it. This is the most cost-effective design change because a read replica offloads the read-heavy workload from the primary Multi-AZ DB instance, directly addressing the CPUUtilization spikes without the expense of scaling up the instance size. Since the application is read-heavy with only occasional writes, the replica handles SELECT traffic while the primary manages writes, improving performance at a lower cost. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of when to scale out versus scale up, and a common trap is choosing a larger instance size, which is more expensive and unnecessary for read-heavy patterns. Remember the memory tip: “Reads go to replicas, writes stay with the primary” to quickly distinguish cost-effective read scaling from vertical scaling.
PAS-C01 Technology Practice Question
This PAS-C01 practice question tests your understanding of technology. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 critical web application on EC2 instances behind an Application Load Balancer. The application uses Auto Scaling and a MySQL RDS Multi-AZ DB instance. Users report intermittent connection timeouts, and CloudWatch metrics show CPUUtilization spikes to 90% on the DB instance. The application queries are read-heavy with occasional writes. What is the MOST cost-effective design change to improve performance?
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
Add an RDS read replica in the same region and configure the application to route read queries to the replica.
Option C is the most cost-effective design change because adding an RDS read replica offloads read-heavy queries from the primary DB instance, reducing CPU utilization without requiring a larger instance. Since the workload is read-heavy with occasional writes, a read replica handles SELECT traffic while the Multi-AZ primary manages writes, improving performance at a lower cost than scaling up.
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.
- ✗
Implement ElastiCache Redis cluster to cache query results and reduce DB load.
Why it's wrong here
Caching adds complexity and cost; for this scenario, a read replica directly addresses the DB CPU spike.
- ✗
Enable RDS Performance Insights and create a CloudWatch alarm to reboot the DB instance on high CPU.
Why it's wrong here
Rebooting does not resolve the root cause of high CPU and causes downtime.
- ✓
Add an RDS read replica in the same region and configure the application to route read queries to the replica.
Why this is correct
A read replica offloads read traffic, reducing CPU on the primary, and is cost-effective for read-heavy workloads.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Switch the DB instance to a larger instance type to handle the load.
Why it's wrong here
Scaling up increases cost; the workload is read-heavy, so a read replica is more cost-effective.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose ElastiCache (Option A) thinking caching always reduces DB load, but for a read-heavy workload with occasional writes, an RDS read replica is more cost-effective and directly addresses the CPU spikes from read queries without the overhead of cache invalidation and additional infrastructure.
Trap categories for this question
Scenario analysis trap
Caching adds complexity and cost; for this scenario, a read replica directly addresses the DB CPU spike.
Detailed technical explanation
How to think about this question
RDS read replicas use asynchronous replication from the primary DB instance to one or more replicas, allowing read queries to be distributed across multiple endpoints. In a read-heavy workload, this reduces CPU contention on the primary instance, as SELECT operations are offloaded, while writes still go to the Multi-AZ primary. Performance Insights can help identify slow queries, but the immediate fix for CPU spikes from read load is to add read capacity via replicas, not to reboot or scale up.
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
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FAQ
Questions learners often ask
What does this PAS-C01 question test?
Technology — This question tests Technology — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add an RDS read replica in the same region and configure the application to route read queries to the replica. — Option C is the most cost-effective design change because adding an RDS read replica offloads read-heavy queries from the primary DB instance, reducing CPU utilization without requiring a larger instance. Since the workload is read-heavy with occasional writes, a read replica handles SELECT traffic while the Multi-AZ primary manages writes, improving performance at a lower cost than scaling up.
What should I do if I get this PAS-C01 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
This PAS-C01 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 PAS-C01 exam.
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