Creating a Step Functions state machine that uses Lambda - AWS Step Functions

Creating a Step Functions state machine that uses Lambda

In this tutorial, you will create a single-step workflow using AWS Step Functions to invoke an AWS Lambda function.


Step Functions is based on state machines and tasks. In Step Functions, a workflow is called a state machine, which is a series of event-driven steps. Each step in a workflow is called a state. A Task state represents a unit of work that another AWS service, such as AWS Lambda, performs. A Task state can call any AWS service or API.

For more information, see:

Lambda is well-suited for Task states, because Lambda functions are serverless and easy to write. You can write code in the AWS Management Console or your favorite editor. AWS handles the details of providing a computing environment for your function and running it.

Step 1: Create a Lambda function

Your Lambda function receives event data and returns a greeting message.


Ensure that your Lambda function is under the same AWS account and AWS Region as your state machine.

  1. Open the Lambda console and choose Create function.

  2. On the Create function page, choose Author from scratch.

  3. For Function name, enter HelloFunction.

  4. Keep the default selections for all other options, and then choose Create function.

  5. After your Lambda function is created, copy the function's Amazon Resource Name (ARN) displayed in the upper-right corner of the page. To copy the ARN, click 
                                        copy Amazon Resource Name
                                    . The following is an example ARN:

  6. Copy the following code for the Lambda function into the Code source section of the HelloFunction page.

    export const handler = async(event, context, callback) => { callback(null, "Hello from " + event.who + "!"); };

    This code assembles a greeting using the who field of the input data, which is provided by the event object passed into your function. You add input data for this function later, when you start a new execution. The callback method returns the assembled greeting from your function.

  7. Choose Deploy.

Step 2: Test the Lambda function

Test your Lambda function to see it in operation.

  1. Choose Test.

  2. For Event name, enter HelloEvent.

  3. Replace the Event JSON data with the following.

    { "who": "AWS Step Functions" }

    The "who" entry corresponds to the event.who field in your Lambda function, completing the greeting. You will input the same input data when you run your state machine.

  4. Choose Save and then choose Test.

  5. To review the test results, under Execution result, expand Details.

Step 3: Create a state machine

Use the Step Functions console to create a state machine that invokes the Lambda function that you created in Step 1.

  1. Open the Step Functions console and choose Create state machine.


    Make sure that your state machine is under the same AWS account and Region as the Lambda function you created earlier.

  2. In the Choose a template dialog box, select Blank.

  3. Choose Select. This opens Workflow Studio in Design mode.

  4. In the States browser on the left, make sure you've chosen the Actions tab. Then, do the following:

    1. Drag and drop the AWS Lambda Invoke API into the empty state labelled Drag first state here.

                                    States browser
  5. In the Inspector panel on the right, configure the Lambda function:

    1. In the API Parameters section, choose the Lambda function that you created earlier in the Function name dropdown list.

    2. Keep the default selection in the Payload dropdown list.

  6. (Optional) Choose Definition to view the state machine's Amazon States Language (ASL) definition, which is automatically generated based on your selections in the Actions tab and Inspector panel.

  7. Specify a name for your state machine. To do this, choose the edit icon next to the default state machine name of MyStateMachine. Then, in State machine settings, specify a name in the State machine name box.

    For example, enter the name LambdaStateMachine.


    State machine, execution, and activity names must be 1–80 characters in length, must be unique for your account and AWS Region, and must not contain any of the following:

    • Whitespace

    • Wildcard characters (? *)

    • Bracket characters (< > { } [ ])

    • Special characters (: ; , \ | ^ ~ $ # % & ` ")

    • Control characters (\\u0000 - \\u001f or \\u007f - \\u009f).

    If your state machine is of type Express, you can provide the same name to multiple executions of the state machine. Step Functions generates a unique execution ARN for each Express state machine execution, even if multiple executions have the same name.

    Step Functions allows you to create state machine, execution, and activity names that contain non-ASCII characters. These non-ASCII names don't work with Amazon CloudWatch. To ensure that you can track CloudWatch metrics, choose a name that uses only ASCII characters.

  8. (Optional) In State machine settings, specify other workflow settings, such as state machine type and its execution role.

    For this tutorial, keep all the default selections in State machine settings.

  9. Choose Create.

  10. In the Confirm role creation dialog box, choose Confirm to continue.

    You can also choose View role settings to go back to State machine settings.


    If you delete the IAM role that Step Functions creates, Step Functions can't recreate it later. Similarly, if you modify the role (for example, by removing Step Functions from the principals in the IAM policy), Step Functions can't restore its original settings later.

Step 4: Run the state machine

After you create your state machine, you can run it.

  1. On the State machines page, choose LambdaStateMachine.

  2. Choose Start execution.

    The Start execution dialog box is displayed.

  3. (Optional) To identify your execution, you can specify a name for it in the Name box. By default, Step Functions generates a unique execution name automatically.


    Step Functions allows you to create state machine, execution, and activity names that contain non-ASCII characters. These non-ASCII names don't work with Amazon CloudWatch. To ensure that you can track CloudWatch metrics, choose a name that uses only ASCII characters.

  4. In the Input area, replace the example execution data with the following.

    { "who" : "AWS Step Functions" }

    "who" is the key name that your Lambda function uses to get the name of the person to greet.

  5. Choose Start Execution.

    Your state machine's execution starts, and a new page showing your running execution is displayed.

  6. The Step Functions console directs you to a page that's titled with your execution ID. This page is known as the Execution Details page. On this page, you can review the execution results as the execution progresses or after it's complete.

    To review the execution results, choose individual states on the Graph view, and then choose the individual tabs on the Step details pane to view each state's details including input, output, and definition respectively. For details about the execution information you can view on the Execution Details page, see Execution Details page – Interface overview.

                            The Output tab of the Step details pane displaying the output returned from the state machine execution.

You can also pass payloads while invoking Lambda from a state machine. For more information and examples about invoking Lambda by passing payload in the Parameters field, see Invoke Lambda with Step Functions.