# Step Functions
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The Step Functions (`stepFunctions`) action starts an AWS Step Functions state machine.

## Requirements
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This rule action has the following requirements:
+ An IAM role that AWS IoT can assume to perform the `states:StartExecution` operation. For more information, see [Granting an AWS IoT rule the access it requires](iot-create-role.md).

  In the AWS IoT console, you can choose or create a role to allow AWS IoT to perform this rule action.

## Parameters
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When you create an AWS IoT rule with this action, you must specify the following information:

`stateMachineName`  
The name of the Step Functions state machine to start.  
Supports [substitution templates](iot-substitution-templates.md): API and AWS CLI only

`executionNamePrefix`  
(Optional) The name given to the state machine execution consists of this prefix followed by a UUID. Step Functions creates a unique name for each state machine execution if one is not provided.  
Supports [substitution templates](iot-substitution-templates.md): Yes

`roleArn`  
The ARN of the role that grants AWS IoT permission to start the state machine. For more information, see [Requirements](#stepfunctions-rule-action-requirements).  
Supports [substitution templates](iot-substitution-templates.md): No

## Examples
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The following JSON example defines a Step Functions action in an AWS IoT rule.

```
{
    "topicRulePayload": {
        "sql": "SELECT * FROM 'some/topic'",
        "ruleDisabled": false,
        "awsIotSqlVersion": "2016-03-23",
        "actions": [
            {
                "stepFunctions": {
                    "stateMachineName": "myStateMachine",
                    "executionNamePrefix": "myExecution",
                    "roleArn": "arn:aws:iam::123456789012:role/aws_iot_step_functions"
                }
            }
        ]
    }
}
```

## See also
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+ [What is AWS Step Functions?](https://docs.aws.amazon.com/step-functions/latest/dg/) in the *AWS Step Functions Developer Guide*