Request Syntax Request Parameters Response Syntax Response Elements Errors See Also

StartExecution

Starts a state machine execution.

A qualified state machine ARN can either refer to a Distributed Map state defined within a state machine, a version ARN, or an alias ARN.

The following are some examples of qualified and unqualified state machine ARNs:

The following qualified state machine ARN refers to a Distributed Map state with a label mapStateLabel in a state machine named myStateMachine.

arn:partition:states:region:account-id:stateMachine:myStateMachine/mapStateLabel

Note
If you provide a qualified state machine ARN that refers to a Distributed Map state, the request fails with ValidationException.
The following qualified state machine ARN refers to an alias named PROD.

arn:<partition>:states:<region>:<account-id>:stateMachine:<myStateMachine:PROD>

Note
If you provide a qualified state machine ARN that refers to a version ARN or an alias ARN, the request starts execution for that version or alias.
The following unqualified state machine ARN refers to a state machine named myStateMachine.

arn:<partition>:states:<region>:<account-id>:stateMachine:<myStateMachine>

If you start an execution with an unqualified state machine ARN, Step Functions uses the latest revision of the state machine for the execution.

To start executions of a state machine version, call StartExecution and provide the version ARN or the ARN of an alias that points to the version.

Note

StartExecution is idempotent for STANDARD workflows. For a STANDARD workflow, if you call StartExecution with the same name and input as a running execution, the call succeeds and return the same response as the original request. If the execution is closed or if the input is different, it returns a 400 ExecutionAlreadyExists error. You can reuse names after 90 days.

StartExecution isn't idempotent for EXPRESS workflows.

Request Syntax


{
   "input": "string",
   "name": "string",
   "stateMachineArn": "string",
   "traceHeader": "string"
}

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.

input

The string that contains the JSON input data for the execution, for example:

"input": "{\"first_name\" : \"test\"}"

Note

If you don't include any JSON input data, you still must include the two braces, for example: "input": "{}"

Length constraints apply to the payload size, and are expressed as bytes in UTF-8 encoding.

Type: String

Length Constraints: Maximum length of 262144.

Required: No

name

Optional name of the execution. This name must be unique for your Amazon account, Region, and state machine for 90 days. For more information, see Limits Related to State Machine Executions in the Amazon Step Functions Developer Guide.

If you don't provide a name for the execution, Step Functions automatically generates a universally unique identifier (UUID) as the execution name.

A name must not contain:

white space
brackets < > { } [ ]
wildcard characters ? *
special characters " # % \ ^ | ~ ` $ & , ; : /
control characters (U+0000-001F, U+007F-009F)

To enable logging with CloudWatch Logs, the name should only contain 0-9, A-Z, a-z, - and _.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 80.

Required: No

stateMachineArn

The Amazon Resource Name (ARN) of the state machine to execute.

The stateMachineArn parameter accepts one of the following inputs:

An unqualified state machine ARN – Refers to a state machine ARN that isn't qualified with a version or alias ARN. The following is an example of an unqualified state machine ARN.

arn:<partition>:states:<region>:<account-id>:stateMachine:<myStateMachine>

Step Functions doesn't associate state machine executions that you start with an unqualified ARN with a version. This is true even if that version uses the same revision that the execution used.
A state machine version ARN – Refers to a version ARN, which is a combination of state machine ARN and the version number separated by a colon (:). The following is an example of the ARN for version 10.

arn:<partition>:states:<region>:<account-id>:stateMachine:<myStateMachine>:10

Step Functions doesn't associate executions that you start with a version ARN with any aliases that point to that version.
A state machine alias ARN – Refers to an alias ARN, which is a combination of state machine ARN and the alias name separated by a colon (:). The following is an example of the ARN for an alias named PROD.

arn:<partition>:states:<region>:<account-id>:stateMachine:<myStateMachine:PROD>

Step Functions associates executions that you start with an alias ARN with that alias and the state machine version used for that execution.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 256.

Required: Yes

traceHeader

Passes the Amazon X-Ray trace header. The trace header can also be passed in the request payload.

Type: String

Length Constraints: Minimum length of 0. Maximum length of 256.

Pattern: \p{ASCII}*

Required: No

Response Syntax


{
   "executionArn": "string",
   "startDate": number
}

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

executionArn

The Amazon Resource Name (ARN) that identifies the execution.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 256.

startDate

The date the execution is started.

Type: Timestamp

Errors

For information about the errors that are common to all actions, see Common Errors.

ExecutionAlreadyExists

The execution has the same name as another execution (but a different input).

Note

Executions with the same name and input are considered idempotent.

HTTP Status Code: 400

ExecutionLimitExceeded

The maximum number of running executions has been reached. Running executions must end or be stopped before a new execution can be started.

HTTP Status Code: 400

InvalidArn

The provided Amazon Resource Name (ARN) is not valid.

HTTP Status Code: 400

InvalidExecutionInput

The provided JSON input data is not valid.

HTTP Status Code: 400

InvalidName

The provided name is not valid.

HTTP Status Code: 400

StateMachineDeleting

The specified state machine is being deleted.

HTTP Status Code: 400

StateMachineDoesNotExist

The specified state machine does not exist.

HTTP Status Code: 400

ValidationException

The input does not satisfy the constraints specified by an Amazon service.

HTTP Status Code: 400