DOP-C02 Monitoring and Logging Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  TargetResponseTime

  Why it's wrong here

  TargetResponseTime is a latency metric that measures the time elapsed from when the load balancer sends a request to a target until it receives the complete response header/body, typically reported as average or percentile. It does not capture status codes or error counts, so it cannot tell you how many requests returned 5xx errors from the origin. Even if response times spike, this metric alone gives no visibility into error frequency or error categories.

• ✗

  UnhealthyHostCount

  Why it's wrong here

  UnhealthyHostCount reports the number of targets that have failed the configured health check thresholds (e.g., consecutive failed ping requests), indicating hosts that are currently out of rotation. While an unhealthy target may generate failed requests, this metric is a count of hosts based on health-check signals, not a sum of HTTP 5xx responses received by the ALB. A target can return 5xx errors during its lifetime while still being marked healthy, so UnhealthyHostCount is not a valid proxy for HTTP error counts.

• ✓

  HTTPCode_Target_5XX_Count

  Why this is correct

  HTTPCode_Target_5XX_Count is the correct choice because it represents the number of HTTP responses with a 5xx status code that were returned by registered targets (e.g., EC2 instances) to the Application Load Balancer. This metric excludes 5xx errors generated by the ALB itself, such as 502 Bad Gateway or 503 Service Unavailable from the load balancer when no healthy targets exist. By checking this metric with a Sum statistic, the engineer can directly quantify application-level server errors and distinguish them from load-balancer-level failures.

• ✗

  RequestCount

  Why it's wrong here

  RequestCount simply increments for every request processed by the ALB regardless of the HTTP status code returned, so it includes successful 2xx, client errors 4xx, and server errors 5xx alike. It is a volume metric useful for understanding traffic load or calculating an error rate when paired with error-specific metrics, but it cannot by itself identify how many 5xx errors occurred. A sudden increase in RequestCount might correlate with an increase in absolute error count, but without a status-code filter it provides no definitive error information.

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