The answer is that the CloudWatch agent is not installed or configured on the EC2 instances. This is the most likely cause because custom metrics require the CloudWatch agent to collect system-level and application-level data and then push it to the CloudWatch service; without the agent running and properly configured, no custom metrics can be sent regardless of other settings. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of the agent’s role as the mandatory data plane component, often tripping candidates who focus solely on IAM permissions or the metric namespace. A common trap is assuming that correct IAM roles alone are sufficient, but the agent must be both installed and actively running on the instance. Remember the memory tip: “No agent, no data” — the agent is the bridge between your EC2 instance and CloudWatch for custom metrics.
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An application running on Amazon EC2 instances sends custom metrics to CloudWatch. The team notices that some metrics are not appearing. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CloudWatch agent is not installed or configured on the EC2 instances.
Option A is correct because the CloudWatch agent must be installed and configured to send custom metrics. Option B is wrong because IAM permissions are required but the agent also needs to be installed. Option C is wrong because the agent needs to be running. Option D is wrong because the metric namespace is configured in the agent, not in CloudWatch.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The custom metric namespace is not pre-registered in CloudWatch.
Why it's wrong here
Namespaces are created automatically when metrics are published.
✗
The EC2 instances are in a private subnet without a NAT gateway.
Why it's wrong here
The agent can use VPC endpoints to reach CloudWatch without internet.
✗
The IAM role attached to the EC2 instance lacks permissions to publish metrics.
Why it's wrong here
This is a common issue, but the agent must also be properly configured.
✓
The CloudWatch agent is not installed or configured on the EC2 instances.
Why this is correct
Custom metrics require the CloudWatch agent or direct API calls.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Monitoring and Logging — This question tests Monitoring and Logging — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The CloudWatch agent is not installed or configured on the EC2 instances. — Option A is correct because the CloudWatch agent must be installed and configured to send custom metrics. Option B is wrong because IAM permissions are required but the agent also needs to be installed. Option C is wrong because the agent needs to be running. Option D is wrong because the metric namespace is configured in the agent, not in CloudWatch.
What should I do if I get this DOP-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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