DBS-C01 Monitoring and Troubleshooting Practice Question
A company uses Amazon DocumentDB (with MongoDB compatibility) for its content management system. The application runs on EC2 instances and connects to a DocumentDB cluster with one instance (db.r5.large). Recently, users reported that retrieving documents takes longer than usual. CloudWatch metrics show that the CPU utilization of the DocumentDB instance is at 90% and the freeable memory is below 100 MB. The team has verified that no query optimization is possible. Which action should the team take FIRST 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
✓
Scale up the instance to db.r5.xlarge.
High CPU utilization (90%) and low freeable memory (<100 MB) indicate that the current instance size (db.r5.large) is insufficient for the workload. Scaling up to db.r5.xlarge provides additional CPU and memory resources, directly addressing the performance bottleneck. Option A (adding a read replica) offloads read traffic but does not reduce CPU/memory pressure on the primary writer. Option B (creating additional indexes) could improve query performance, but the team has verified that no query optimization is possible. Option C (increasing storage volume) improves I/O performance but does not directly affect CPU or memory usage.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add a read replica instance to offload read traffic.
Why it's wrong here
Adding a read replica helps distribute read traffic but does not reduce CPU or memory pressure on the primary writer, so it does not address the immediate bottleneck.
- ✗
Create additional indexes on frequently queried fields.
Why it's wrong here
Creating additional indexes could improve query performance, but the team has already verified that no query optimization is possible, so this is not a viable first step.
- ✗
Increase the storage volume size to improve I/O performance.
Why it's wrong here
Increasing storage volume size improves I/O performance but does not directly affect CPU utilization or freeable memory.
- ✓
Scale up the instance to db.r5.xlarge.
Why this is correct
Scaling up to a larger instance (db.r5.xlarge) provides more CPU and memory resources, directly addressing the high CPU and low memory issues.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.