AWS DVA-C02 Drill: Lambda Logging - Capturing Invocation IDs Correctly

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in which Lambda object holds the unique request ID. In production-grade Lambda observability, knowing you must extract the AWS request ID from the context object rather than the event payload is essential to reliably correlate logs. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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InnoTech Solutions is developing a serverless payment processing system using AWS Lambda functions triggered by API Gateway. The lead developer wants to improve troubleshooting by logging key lifecycle events during each Lambda invocation. Crucially, each log entry must include a unique identifier to tie the logs back to a specific invocation.

The Requirement:

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Implement a logging solution that includes the unique request identifier for every Lambda invocation. The identifier should reliably associate all logs with the precise function execution.

The Options

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• A) Obtain the request identifier from the AWS request ID field in the context object. Configure the application to write logs to standard output.
• B) Obtain the request identifier from the AWS request ID field in the event object. Configure the application to write logs to a file.
• C) Obtain the request identifier from the AWS request ID field in the event object. Configure the application to write logs to standard output.
• D) Obtain the request identifier from the AWS request ID field in the context object. Configure the application to write logs to a file.

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leave a comment:

Correct Answer

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A.

Quick Insight: The Developer Imperative

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• The AWS Lambda runtime injects a unique request ID with each invocation into the context object, not the event. This ID should be logged to standard output, as Lambda automatically routes stdout/stderr logs to Amazon CloudWatch Logs.
• Writing logs to a file within Lambda is discouraged, as the execution environment is ephemeral and temporary files are not durable or centralized for aggregation.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option A

The Winning Logic

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The AWS Lambda runtime provides a context object to every handler invocation, which contains an awsRequestId property that uniquely identifies that specific function invocation. Logging this identifier allows developers to trace all logs related to a single transaction or request.

• The event object contains the input event data but does not include the Lambda request ID.
• Logging must be sent to standard output (stdout or stderr) so that Lambda can capture and forward the logs automatically to CloudWatch.
• Writing logs to a file inside Lambda is unreliable since the ephemeral file system is not retained across invocations and not monitored by CloudWatch by default.

Adopting this approach enables seamless correlation of logs with distributed tracing and monitoring tools like AWS X-Ray and CloudWatch Logs.

The Trap (Distractor Analysis):

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• Why not B or C? The Lambda request ID is not part of the event input. Attempting to get it from event results in undefined or missing identifiers.
• Why not D? Logging to a file inside Lambda won’t be automatically aggregated and adds unnecessary operational complexity since Lambda functions do not maintain persistent storage.

The Technical Blueprint

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Code Snippet Example for DVA-C02 Developers

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exports.handler = async (event, context) => {
  const requestId = context.awsRequestId;  // Correct source of the request ID

  // Log key event with request ID included
  console.log(`Request ID: ${requestId} - Processing started`);

  // Function logic here...

  console.log(`Request ID: ${requestId} - Processing completed`);
  return { statusCode: 200, body: 'Success' };
};

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the exam, always retrieve the invocation ID from the context object and write logs to standard output in Lambda.”

Real World

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“In production, centralized logging and monitoring tools (like CloudWatch Logs, X-Ray) rely on this pattern to provide observability across distributed systems.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.