Merge Step Functions and Lambda Traces

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This page describes how to merge your AWS Step Functions traces with related AWS Lambda traces or nested Step Functions traces. These instructions assume that you have already instrumented these AWS Step Functions and Lambda functions to send traces to Datadog.

Merge Step Functions traces with downstream Lambda traces

Requirements

Node.js (layer v112+) or Python (layer v95+) runtimes.

Setup

In your serverless.yaml file, set mergeStepFunctionAndLambdaTraces to true. For example:

custom:
  datadog:
    site: <DATADOG_SITE>
    apiKeySecretArn: <DATADOG_API_KEY_SECRET_ARN>
    forwarderArn: <FORWARDER_ARN>
    enableStepFunctionsTracing: true
    propagateUpstreamTrace: true
    mergeStepFunctionAndLambdaTraces: true

Run the following datadog-ci command:

datadog-ci stepfunctions instrument \
 --step-function <STEP_FUNCTION_ARN> \
 --forwarder <FORWARDER_ARN> \
 --env <ENVIRONMENT> \
 --propagate-upstream-trace \
 --merge-step-function-and-lambda-traces

The merge-step-function-and-lambda-traces flag lets you inject Step Functions context into downstream Lambda and Step Functions invocations.

On the Lambda Task, set the Parameters key as follows:

"Parameters": {
  "Payload.$": "States.JsonMerge($$, $, false)",
  ...
}

The JsonMerge intrinsic function merges the Step Functions context object ($$) with the original Lambda’s input payload ($). Fields of the original payload overwrite the Step Functions context object if their keys are the same.

Example:

"Lambda Read From DynamoDB": {
  "Type": "Task",
  "Resource": "arn:aws:states:::lambda:invoke",
  "Parameters": {
    "Payload.$": "States.JsonMerge($$, $, false)",
    "FunctionName": "${lambdaArn}"
  },
  "End": true
}

Alternatively, if you have business logic defined in the payload, you can also use the following format:

"Lambda Read From DynamoDB": {
  "Type": "Task",
  "Resource": "arn:aws:states:::lambda:invoke",
  "Parameters": {
    "Payload": {
      ...
      "Execution.$": "$$.Execution",
      "State.$": "$$.State",
      "StateMachine.$": "$$.StateMachine"
    },
    "FunctionName": "${lambdaArn}"
  },
  "End": true
}

Merge upstream Lambda traces with Step Functions traces

Requirements

For Node.js: Datadog Lambda Library for Node.js layer v112+ or dd-trace-js v3.58.0, v4.37.0, v5.13.0.

For Python: Datadog Lambda Library for Python layer 99+ or dd-trace-py v2.13.0.

Setup

If the layer or tracer version requirements are fulfilled, no further setup is required.

To ensure proper trace merging, provide input to the Step Functions Start Execution command, even if the input is an empty JSON object.

Merge Step Functions traces with nested Step Functions traces

To link your Step Function traces to nested Step Function traces, configure your task according to the following example:

"Step Functions StartExecution": {
  "Type": "Task",
  "Resource": "arn:aws:states:::states:startExecution",
  "Parameters": {
    "StateMachineArn": "${stateMachineArn}",
    "Input": {
      "StatePayload": "Hello from Step Functions!",
      "CONTEXT": {
        "Execution.$": "$$.Execution",
        "State.$": "$$.State",
        "StateMachine.$": "$$.StateMachine"
      }
    }
  },
  "End": true
}

Merge Lambda -> Step Functions -> Lambda

This capability is not supported.