Merge Step Functions and Lambda Traces

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.

Datadog recommends using JSONata to define your Step Function payloads for the most complete end-to-end tracing experience. If you are using JSONPath to define your Step Function payloads, see the below sections for supported configurations.

Merge upstream traces with Step Functions and downstream Lambda traces

Requirements

Node.js (layer v116+) or Python (layer v103+) runtimes.

Your State Machine Definition must be using JSONata as the query language. This can be enabled by setting "QueryLanguage": "JSONata" at the top-level of the State Machine Definition.

Setup

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

"Arguments": {
  "Payload": "{% ($execInput := $states.context.Execution.Input; $hasDatadogTraceId := $exists($execInput._datadog.`x-datadog-trace-id`); $hasDatadogRootExecutionId := $exists($execInput._datadog.RootExecutionId); $ddTraceContext := $hasDatadogTraceId ? {'x-datadog-trace-id': $execInput._datadog.`x-datadog-trace-id`, 'x-datadog-tags': $execInput._datadog.`x-datadog-tags`} : {'RootExecutionId': $hasDatadogRootExecutionId ? $execInput._datadog.RootExecutionId : $states.context.Execution.Id}; $sfnContext := $merge([$states.context, {'Execution': $sift($states.context.Execution, function($v, $k) { $k != 'Input' })}]); $merge([$states.input, {'_datadog': $merge([$sfnContext, $ddTraceContext, {'serverless-version': 'v1'}])}])) %}",
  ...
}

The JSONata expression merges the upstream service’s context with the current Step Functions context object and the Lambda state’s input payload.

Alternatively, if you have business logic defined in the payload, you can replace $states.input at the end of the JSONata expression with your intended value for the Payload key.

Merge upstream traces with Step Functions and nested Step Functions traces

Requirements

Your State Machine Definition must be using JSONata as the query language. This can be enabled by setting "QueryLanguage": "JSONata" at the top-level of the State Machine Definition.

Setup

On the Step Functions Task, set the _datadog field in the Input key as follows:

"Arguments": {
  "Input": {
    "_datadog": "{% ($execInput := $states.context.Execution.Input; $hasDatadogTraceId := $exists($execInput._datadog.`x-datadog-trace-id`); $hasDatadogRootExecutionId := $exists($execInput._datadog.RootExecutionId); $ddTraceContext := $hasDatadogTraceId ? {'x-datadog-trace-id': $execInput._datadog.`x-datadog-trace-id`, 'x-datadog-tags': $execInput._datadog.`x-datadog-tags`} : {'RootExecutionId': $hasDatadogRootExecutionId ?  $execInput._datadog.RootExecutionId : $states.context.Execution.Id}; $sfnContext := $merge([$states.context, {'Execution': $sift($states.context.Execution, function($v, $k) { $k != 'Input' })}]); $merge([$sfnContext, $ddTraceContext, {'serverless-version': 'v1'}])) %}",
    ...
  }
}

Merge Step Functions traces with downstream Lambda traces

Requirements

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

Setup

  1. If you have not already, install the Datadog Serverless Framework Plugin v5.40.0+:

    serverless plugin install --name serverless-plugin-datadog

  2. Ensure you have deployed the Datadog Lambda Forwarder, a Lambda function that ships logs from AWS to Datadog, and that you are using v3.130.0+. You might need to update your Forwarder.

    Take note of your Forwarder’s ARN.

  3. Add the following to your serverless.yml:

    custom:
  datadog:
    site: <DATADOG_SITE>
    apiKeySecretArn: <DATADOG_API_KEY_SECRET_ARN>
    forwarderArn: <FORWARDER_ARN>
    enableStepFunctionsTracing: true
    propagateUpstreamTrace: true
    mergeStepFunctionAndLambdaTraces: true
    • Replace <DATADOG_SITE> with datadoghq.com (ensure the correct SITE is selected on the right).
    • Replace <DATADOG_API_KEY_SECRET_ARN> with the ARN of the AWS secret where your Datadog API key is securely stored. The key needs to be stored as a plaintext string (not a JSON blob). The secretsmanager:GetSecretValue permission is required. For quick testing, you can instead use apiKey and set the Datadog API key in plaintext.
    • Replace <FORWARDER_ARN> with the ARN of your Datadog Lambda Forwarder. This step configures the log stream subscription for the Forwarder. Ensure that the Step Function log group name begins with “/aws/vendedlogs/states/”. If it does not, you will need to set it up manually.

    For additional settings, see Datadog Serverless Framework Plugin - Configuration parameters.

  1. If you have not already, install the Datadog CLI v2.18.0+.

    npm install -g @datadog/datadog-ci

  2. Ensure you have deployed the Datadog Lambda Forwarder, a Lambda function that ships logs from AWS to Datadog, and that you are using v3.130.0+. You may need to update your Forwarder.

    Take note of your Forwarder’s ARN.

  3. Instrument your Step Function.

    datadog-ci stepfunctions instrument \
 --step-function <STEP_FUNCTION_ARN> \
 --forwarder <FORWARDER_ARN> \
 --env <ENVIRONMENT> \
 --propagate-upstream-trace \
 --merge-step-function-and-lambda-traces
    • Replace <STEP_FUNCTION_ARN> with the ARN of your Step Function. Repeat the --step-function flag for each Step Function you wish to instrument.
    • Replace <FORWARDER_ARN> with the ARN of your Datadog Lambda Forwarder, as noted previously. This step configures the log stream subscription for the Forwarder. Ensure that the Step Function log group name begins with “/aws/vendedlogs/states/”. If it does not, you will need to set it up manually.
    • Replace <ENVIRONMENT> with the environment tag you would like to apply to your Step Functions.

    For more information about the datadog-ci stepfunctions command, see the Datadog CLI documentation.

Modify your Lambda task payload or Step Function task input.

Example:

from aws_cdk import (
    aws_lambda,
    aws_stepfunctions as sfn,
    aws_stepfunctions_tasks as tasks,
)
from datadog_cdk_constructs_v2 import DatadogStepFunctions, DatadogLambda

lambda_function = aws_lambda.Function(...)
lambda_task = tasks.LambdaInvoke(
    self,
    "MyLambdaTask",
    lambda_function=lambda_function,
    payload=sfn.TaskInput.from_object(
        DatadogStepFunctions.build_lambda_payload_to_merge_traces(
            {"custom-key": "custom-value"}
        )
    ),
)

child_state_machine = sfn.StateMachine(...)
invoke_child_state_machine_task = tasks.StepFunctionsStartExecution(
    self,
    "InvokeChildStateMachineTask",
    state_machine=child_state_machine,
    input=sfn.TaskInput.from_object(
        DatadogStepFunctions.build_step_function_task_input_to_merge_traces(
            {"custom-key": "custom-value"}
        )
    ),
)

state_machine = sfn.StateMachine(
    self,
    "CdkPythonTestStateMachine",
    definition_body=sfn.DefinitionBody.from_chainable(
        lambda_task.next(invoke_child_state_machine_task)
    ),
)

datadog_lambda = DatadogLambda(...)
datadog_lambda.add_lambda_functions([lambda_function])

datadog_sfn = DatadogStepFunctions(...)
datadog_sfn.add_state_machines([child_state_machine, state_machine])

For additional code examples in TypeScript and Go, see CDK Examples for Instrumenting AWS Step Functions.

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
}

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