DVA-C02 Troubleshooting and Optimization Practice Question
An API backed by Lambda returns high p95 latency after deployment. Which two telemetry sources are most useful first?
⚠ Common exam trap
The trap here is that candidates often overlook the combination of CloudWatch metrics and X-Ray traces, mistakenly thinking that only one telemetry source (like CloudWatch logs) is sufficient, or they confuse billing data with performance monitoring.
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
✓
CloudWatch Lambda duration/init duration/logs
CloudWatch Lambda duration and init duration metrics directly measure the time your function spends executing and initializing, which are the primary drivers of p95 latency. Logs can reveal cold starts, timeouts, or inefficient code paths that cause high latency. These are the most immediate telemetry sources to identify performance bottlenecks in the Lambda function itself.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AWS Billing console only
Why it's wrong here
The AWS Billing console primarily provides cost and usage reports, focusing on financial aspects rather than operational performance. While high latency might indirectly influence costs by increasing resource consumption, it offers no direct metrics or diagnostic tools to identify the root causes of p95 latency within an API Gateway or Lambda function. Therefore, it is unsuitable for performance troubleshooting.
- ✓
CloudWatch Lambda duration/init duration/logs
Why this is correct
CloudWatch provides critical metrics like `Duration` and `Init Duration` for Lambda functions, directly revealing execution and cold start times. Analyzing the p95 percentile of these metrics pinpoints specific latency bottlenecks. Furthermore, detailed CloudWatch Logs offer granular insights into the function's internal execution flow, external service calls, and potential code-level inefficiencies contributing to high latency.
- ✗
S3 Inventory reports
Why it's wrong here
S3 Inventory reports are designed for auditing and managing objects within Amazon S3 buckets, providing lists of objects, their metadata, and encryption status. These reports are entirely unrelated to the performance of API Gateway or Lambda functions. They offer no insights into request latency, execution duration, or any other metrics pertinent to diagnosing high p95 latency in an API backend.
- ✓
X-Ray traces across API Gateway and Lambda
Why this is correct
AWS X-Ray delivers end-to-end visibility by tracing requests across distributed components, including API Gateway and Lambda. It visualizes the entire request path, highlighting latency contributions from each segment, such as database calls or external API integrations. This comprehensive tracing is invaluable for identifying the exact bottlenecks responsible for high p95 latency across the entire transaction flow.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-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 DVA-C02 exam.