Invoke an Amazon Lambda function with Step Functions

Learn how to use Step Functions to invoke Lambda functions either synchronously or asynchronously as part of an event-driven serverless application.

Step Functions can control certain Amazon services directly from Using Amazon States Language to define Step Functions workflows (ASL). To learn more, see Integrating other services and Passing parameters to a service API in Step Functions.

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

Supported Amazon Lambda APIs:

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

{  
   "StartAt":"CallLambda",
   "States":{  
      "CallLambda":{  
         "Type":"Task",
         "Resource":"arn:aws-cn:states:::lambda:invoke",
         "Parameters":{  
            "FunctionName":"arn:aws-cn: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-cn:states:::lambda:invoke.waitForTaskToken",
         "Parameters":{  
            "FunctionName":"arn:aws-cn: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:

{

  "Comment": "A Hello World example of the Amazon States Language using Pass states",
  "StartAt": "Hello",
  "States": {
    "Hello": {
      "Type": "Task",
      "Resource": "arn:aws-cn:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "arn:aws-cn: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-cn: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 Amazon services, see How Step Functions generates IAM policies for integrated services.