The answer is to scale up the instance to db.r5.xlarge. This is correct because the CloudWatch metrics show CPU utilization at 90% and freeable memory below 100 MB, which means the current db.r5.large instance is resource-constrained and cannot handle the workload, even after ruling out query optimization. Scaling up provides more vCPUs and memory, directly addressing the bottleneck by giving the primary instance more capacity to process requests and cache data. On the AWS Certified Database Specialty DBS-C01 exam, this tests your understanding of vertical scaling versus horizontal scaling: a common trap is choosing to add a reader replica, which only helps with read traffic but does not relieve CPU or memory pressure on the single writer. Remember the mnemonic “High CPU, low RAM? Scale up the ham.” — when the primary instance is overloaded, increase its size before adding complexity.
DBS-C01 Monitoring and Troubleshooting Practice Question
This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. 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 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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Add a read replica instance to offload read traffic.
Why wrong: Read replicas can offload reads but the primary still handles writes and may remain overloaded. The issue is likely write-heavy or mixed workload.
B
Create additional indexes on frequently queried fields.
Why wrong: The team verified no query optimization is possible; creating indexes may not help and could even increase write overhead.
C
Increase the storage volume size to improve I/O performance.
Why wrong: Storage increase does not affect CPU or memory; the bottleneck is compute resources.
D
Scale up the instance to db.r5.xlarge.
A larger instance provides more CPU and memory, directly addressing the resource exhaustion.
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.
Option B is correct because the high CPU and low memory indicate the instance is overworked. Scaling up to a larger instance provides more CPU and memory resources. Option A is incorrect because adding a reader instance helps with read scaling but does not reduce CPU/memory pressure on the primary writer. Option C is incorrect because creating an index may improve query performance but the team already ruled out query optimization. Option D is incorrect because increasing storage does not directly affect CPU or memory.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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
Read replicas can offload reads but the primary still handles writes and may remain overloaded. The issue is likely write-heavy or mixed workload.
✗
Create additional indexes on frequently queried fields.
Why it's wrong here
The team verified no query optimization is possible; creating indexes may not help and could even increase write overhead.
✗
Increase the storage volume size to improve I/O performance.
Why it's wrong here
Storage increase does not affect CPU or memory; the bottleneck is compute resources.
✓
Scale up the instance to db.r5.xlarge.
Why this is correct
A larger instance provides more CPU and memory, directly addressing the resource exhaustion.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Monitoring and Troubleshooting — This question tests Monitoring and Troubleshooting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Scale up the instance to db.r5.xlarge. — Option B is correct because the high CPU and low memory indicate the instance is overworked. Scaling up to a larger instance provides more CPU and memory resources. Option A is incorrect because adding a reader instance helps with read scaling but does not reduce CPU/memory pressure on the primary writer. Option C is incorrect because creating an index may improve query performance but the team already ruled out query optimization. Option D is incorrect because increasing storage does not directly affect CPU or memory.
What should I do if I get this DBS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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