DOP-C02 Monitoring and Logging Practice Question
A company runs an internal REST API on Amazon API Gateway backed by AWS Lambda. The operations team wants a single CloudWatch alarm that fires when the API's overall error rate exceeds 5% during any 5-minute period, without creating one alarm per resource. The API is deployed as a REST API (not HTTP API). Which approach should a DevOps engineer take?
⚠ Common exam trap
The trap here is assuming API Gateway exposes a ready-made percentage error metric, when in fact you must compute the ratio yourself with metric math.
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
✓
Create a CloudWatch metric math alarm using the expression m1/m2 where m1 is the sum of the 4XXError and 5XXError metrics and m2 is the Count metric for the stage, all with period 300 and statistic Sum.
API Gateway publishes 4XXError, 5XXError, and Count per stage. A metric math alarm can sum the error metrics and divide by Count at a five-minute period, producing a single stage-level error-rate alarm. Per-method alarms, X-Ray metrics, and log metric filters either fragment the view or do not directly yield a percentage.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable AWS X-Ray tracing on the stage and create a CloudWatch alarm on the X-Ray ErrorRate metric for the API.
Why it's wrong here
X-Ray publishes its own service metrics, but those are not the API Gateway error-rate metrics used for the 5% threshold, and enabling tracing changes sampling behavior rather than producing a stage-level alarm in one step. The team would still need a separate aggregation mechanism, so this does not satisfy the single-alarm requirement.
- ✓
Create a CloudWatch metric math alarm using the expression m1/m2 where m1 is the sum of the 4XXError and 5XXError metrics and m2 is the Count metric for the stage, all with period 300 and statistic Sum.
Why this is correct
Metric math lets a single alarm combine several API Gateway metrics. Summing 4XXError and 5XXError and dividing by Count at a 300-second period yields the stage-level error rate, so one alarm covers the whole API rather than one alarm per method or resource. This directly satisfies the 5% threshold requirement.
- ✗
Create one CloudWatch alarm per method with a 5% threshold and combine them into a composite alarm using an OR rule.
Why it's wrong here
Composite alarms can combine children, but the requirement is a single alarm on the overall API error rate, not a per-method set. This approach scales with the number of methods and still needs the rate math inside each child alarm, so it is more complex than necessary and does not aggregate at the stage level.
- ✗
Create a CloudWatch Logs metric filter on the API Gateway access logs and alarm on the resulting custom metric with a 5% threshold.
Why it's wrong here
Metric filters extract values from log events; they do not produce a ratio of errors to total requests natively. Access logging must also be enabled first, and deriving a true percentage would still require metric math or two metrics. This is a valid pattern for counts, but not the cleanest way to alarm on a rate.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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.