Invoke Lambda with Step Functions - AWS Step Functions

Invoke Lambda with Step Functions

Step Functions can control certain AWS services directly from the Amazon States Language (ASL). For more information about working with AWS Step Functions and its integrations, see the following:

How the Optimized Lambda integration is different than the Lambda AWS SDK integration
  • The Payload field of the response is parsed from escaped Json to Json.

  • If the response contains the field FunctionError or an exception is raised within the Lambda function, the task fails.

For more information about managing state input, output, and results, see Input and Output Processing in Step Functions.

Supported AWS Lambda APIs:


Parameters in Step Functions are expressed in PascalCase, even if the native service API is in camelCase. For example, you could use the Step Functions API action startSyncExecution and specify its parameter as StateMachineArn.

The following includes a Task state that invokes a Lambda function.

{ "StartAt":"CallLambda", "States":{ "CallLambda":{ "Type":"Task", "Resource":"arn:aws:states:::lambda:invoke", "Parameters":{ "FunctionName":"arn:aws:lambda:us-east-1:123456789012:function:MyFunction" }, "End":true } } }

The following includes a Task state that implements the callback service integration pattern.

{ "StartAt":"GetManualReview", "States":{ "GetManualReview":{ "Type":"Task", "Resource":"arn:aws:states:::lambda:invoke.waitForTaskToken", "Parameters":{ "FunctionName":"arn:aws:lambda:us-east-1:123456789012:function:get-model-review-decision", "Payload":{ "model.$":"$.new_model", "token.$":"$$.Task.Token" }, "Qualifier":"prod-v1" }, "End":true } } }

When you invoke a Lambda function, the execution will wait for the function to complete. If you invoke the Lambda function with a callback task, the heartbeat timeout doesn't start counting until after the Lambda function has completed executing and returned a result. As long as the Lambda function executes, the heartbeat timeout is not enforced.

It is also possible to call Lambda asynchronously using the InvocationType parameter, as seen in the following example:


For asynchronous invocations of Lambda functions, the heartbeat timeout period starts immediately.

{ "Comment": "A Hello World example of the Amazon States Language using Pass states", "StartAt": "Hello", "States": { "Hello": { "Type": "Task", "Resource": "arn:aws:states:::lambda:invoke", "Parameters": { "FunctionName": "arn:aws:lambda:us-east-1:123456789012:function:echo", "InvocationType": "Event" }, "End": true } } }

When the Task result is returned, the function output is nested inside a dictionary of metadata. For example:

{ "ExecutedVersion":"$LATEST", "Payload":"FUNCTION OUTPUT", "SdkHttpMetadata":{ "HttpHeaders":{ "Connection":"keep-alive", "Content-Length":"4", "Content-Type":"application/json", "Date":"Fri, 26 Mar 2021 07:42:02 GMT", "X-Amz-Executed-Version":"$LATEST", "x-amzn-Remapped-Content-Length":"0", "x-amzn-RequestId":"0101aa0101-1111-111a-aa55-1010aaa1010", "X-Amzn-Trace-Id":"root=1-1a1a000a2a2-fe0101aa10ab;sampled=0" }, "HttpStatusCode":200 }, "SdkResponseMetadata":{ "RequestId":"6b3bebdb-9251-453a-ae45-512d9e2bf4d3" }, "StatusCode":200 }

Alternatively, you can invoke a Lambda function by specifying a function ARN directly in the "Resource" field. When you invoke a Lambda function in this way, you can't specify .waitForTaskToken, and the task result contains only the function output.

{ "StartAt":"CallFunction", "States":{ "CallFunction": { "Type":"Task", "Resource":"arn:aws:lambda:us-east-1:123456789012:function:HelloFunction", "End": true } } }

You can invoke a specific Lambda function version or alias by specifying those options in the ARN in the Resource field. See the following in the Lambda documentation:

For information about how to configure IAM permissions when using Step Functions with other AWS services, see IAM Policies for integrated services.