Quick Answer
The answer is HTTPCode_Target_5XX_Count, because this CloudWatch metric specifically tracks HTTP 5xx status codes returned directly by the backend targets, such as EC2 instances, while HTTPCode_ELB_5XX_Count isolates errors generated by the Application Load Balancer itself, such as when it cannot establish a connection to an unhealthy target. To differentiate between ALB 5xx errors and target errors, you compare these two metrics: a spike in the target metric points to application-level failures like timeouts or internal server errors, whereas a spike in the ELB metric indicates infrastructure issues like insufficient capacity or misconfigured security groups. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this concept tests your ability to troubleshoot load balancer error sources without relying on application logs, and a common trap is confusing UnhealthyHostCount, which only flags health check failures, not specific error codes. A reliable memory tip is to remember that “Target” in the metric name means the error comes from the target, while “ELB” means the load balancer itself is the source.
This DOP-C02 practice question tests your understanding of monitoring and logging. 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 DevOps engineer manages a production environment with EC2 instances behind an Application Load Balancer (ALB). The application logs show intermittent 5xx errors from the ALB. The engineer needs to identify whether the errors originate from the targets or the ALB itself. Which CloudWatch metric should be examined to differentiate between these two sources?
TargetResponseTime
Why wrong: This measures response time, not errors.
UnhealthyHostCount
Why wrong: This indicates health check failures, not HTTP error codes.
HTTPCode_Target_5XX_Count
This metric counts 5xx responses from targets, distinguishing from ALB-originated 5xx.
RequestCount
Why wrong: This is total requests, not error-specific.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
HTTPCode_Target_5XX_Count
Option B is correct because HTTPCode_Target_5XX_Count indicates errors from the target (EC2 instances), while HTTPCode_ELB_5XX_Count indicates errors from the ALB. Option A is wrong because RequestCount is total requests. Option C is wrong because TargetResponseTime measures latency. Option D is wrong because UnhealthyHostCount indicates unhealthy targets, not specific error codes.
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
For each option: why learners choose it and why it is or isn't the right answer here.
TargetResponseTime
Why it's wrong here
This measures response time, not errors.
UnhealthyHostCount
Why it's wrong here
This indicates health check failures, not HTTP error codes.
HTTPCode_Target_5XX_Count
RequestCount
Why it's wrong here
This is total requests, not error-specific.
Common exam traps
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
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.
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
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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 DOP-C02 NAT questions on configuration and troubleshooting.
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FAQ
Monitoring and Logging — This question tests Monitoring and Logging — Static NAT maps one inside address to one outside address..
The correct answer is: HTTPCode_Target_5XX_Count — Option B is correct because HTTPCode_Target_5XX_Count indicates errors from the target (EC2 instances), while HTTPCode_ELB_5XX_Count indicates errors from the ALB. Option A is wrong because RequestCount is total requests. Option C is wrong because TargetResponseTime measures latency. Option D is wrong because UnhealthyHostCount indicates unhealthy targets, not specific error codes.
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 DOP-C02 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
This DOP-C02 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 DOP-C02 exam.
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