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. 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, 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:

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":"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":"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. However, it is 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:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "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 on how to configure IAM when using Step Functions with other AWS services, see IAM Policies for integrated services.