Instrumenting Node.js Code in AWS Lambda

In Node.js, you can have Lambda emit subsegments to X-Ray to show you information about downstream calls to other AWS services made by your function. To do so, you first need to include the the AWS X-Ray SDK for Node.js in your deployment package. In addition, wrap your AWS SDK require statement in the following manner.

const AWSXRay = require('aws-xray-sdk-core')
const AWS = AWSXRay.captureAWS(require('aws-sdk'))

Then, use the AWS variable defined in the preceding example to initialize any service client that you want to trace with X-Ray, for example:

const s3 = new AWS.S3()

After following these steps, any call made from your function using s3Client results in an X-Ray subsegment that represents that call. As an example, you can run the Node.js function following to see how the trace looks in X-Ray.

Example index.js

const AWSXRay = require('aws-xray-sdk-core')
const AWS = AWSXRay.captureAWS(require('aws-sdk'))
const s3 = new AWS.S3()

exports.handler = async function(event) {
  return s3.listBuckets().promise()
}

Following is what a trace emitted by the code preceding looks like.