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Difficulty: MediumInstrumenting Distributed Tracing with AWS X-Ray

A developer has a serverless application consisting of Amazon API Gateway, an AWS Lambda function, and an Amazon DynamoDB table. The developer enables active tracing on both the API Gateway stage and the Lambda function. However, when inspecting the AWS X-Ray service map, the developer notices that downstream DynamoDB service calls are missing from the trace path. Which of the following actions is required to ensure that DynamoDB calls are included in the distributed trace?

  1. Instrument the AWS SDK client inside the Lambda function code using the AWS X-Ray SDK to capture downstream calls.Answer
  2. B
    Rely solely on the active tracing setting in the Lambda function configuration, as this automatically instruments all downstream AWS SDK clients.
  3. C
    Hardcode an IAM user access key and secret key with AWS X-Ray write permissions directly in the Lambda function initialization code.
  4. D
    Increase the Amazon SQS visibility timeout of the downstream queue to allow the X-Ray daemon more time to buffer trace segments.

Answer

Instrument the AWS SDK client inside the Lambda function code using the AWS X-Ray SDK to capture downstream calls.
The correct answer is to instrument the AWS SDK client inside the Lambda function code using the AWS X-Ray SDK. Enabling active tracing on Lambda only enables tracing of the function invocation itself. To trace downstream calls to other AWS resources, the AWS SDK client must be explicitly instrumented using the AWS X-Ray SDK so that the trace context is passed and recorded.

Step-by-Step Solution

1
Identify the missing segment in the distributed trace.
The AWS X-Ray service map shows the API Gateway and Lambda function, but not the calls made from the Lambda function to DynamoDB.
Although active tracing is enabled on the Lambda function, the Lambda runtime only records the inbound request unless the client libraries are instrumented to propagate the tracing header.
2
Add the AWS X-Ray SDK to the project dependencies and instrument the AWS SDK client.
The AWS SDK client is wrapped or instrumented (e.g., using the AWS X-Ray SDK's capture helper) before initializing the DynamoDB client.
This wrapping automatically records downstream metadata, latency, and HTTP status code details for each DynamoDB call and associates them with the parent tracing segment.
3
Deploy the Lambda function and test the API integration.
The updated traces now include the DynamoDB node on the service map and the corresponding subsegments in the trace details.
The instrumented SDK automatically extracts the tracing header from the Lambda environment and passes it along to the DynamoDB endpoint.

Key Concept

Instrumenting AWS SDK clients in code is required to trace downstream service calls in AWS X-Ray.
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Topics

Instrumenting Distributed Tracing with AWS X-Ray

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