Task state - Amazon Step Functions
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Task state

A Task state ("Type": "Task") represents a single unit of work performed by a state machine. A task performs work by using an activity or an Amazon Lambda function, by integrating with other supported Amazon Web Services, or by invoking a third-party API, such as Stripe.

The Amazon States Language represents tasks by setting a state's type to Task and by providing the task with the Amazon Resource Name (ARN) of the activity, Lambda function, or the third-party API endpoint. The following Task state definition invokes a Lambda function named HelloFunction.

"Lambda Invoke": { "Type": "Task", "Resource": "arn:aws-cn:states:::lambda:invoke", "Parameters": { "Payload.$": "$", "FunctionName": "arn:aws-cn:lambda:us-west-2:123456789012:function:HelloFunction:$LATEST" }, "End": true }

Task types

Step Functions supports the following task types that you can specify in a Task state definition:

You specify a task type by providing its ARN in the Resource field of a Task state definition. The following example shows the syntax of the Resource field. All Task types except the one that invokes an third-party API, use the following syntax. For information about syntax of the HTTP Task, see Call third-party APIs.

In your Task state definition, replace the italicized text in the following syntax with the Amazon resource-specific information.

arn:partition:service:region:account:task_type:name

The following list explains the individual components in this syntax:

  • partition is the Amazon Step Functions partition to use, most commonly aws.

  • service indicates the Amazon Web Service used to execute the task, and can be one of the following values:

    • states for an activity.

    • lambda for a Lambda function. If you integrate with other Amazon Web Services, for example, Amazon SNS or Amazon DynamoDB, use sns or dynamodb.

  • region is the Amazon Region code in which the Step Functions activity or state machine type, Lambda function, or any other Amazon resource has been created.

  • account is the Amazon Web Services account ID in which you've defined the resource.

  • task_type is the type of task to run. It can be one of the following values:

  • name is the registered resource name (activity name, Lambda function name, or service API action).

Note

Step Functions doesn't support referencing ARNs across partitions or regions. For example, aws-cn can't invoke tasks in the aws partition, and the other way around.

The following sections provide more detail about each task type.

Activity

Activities represent workers (processes or threads), implemented and hosted by you, that perform a specific task. They are supported only by Standard Workflows, not Express Workflows.

Activity Resource ARNs use the following syntax.

arn:partition:states:region:account:activity:name
Note

You must create activities with Step Functions (using a CreateActivity, API action, or the Step Functions console) before their first use.

For more information about creating an activity and implementing workers, see Activities.

Lambda functions

Lambda tasks execute a function using Amazon Lambda. To specify a Lambda function, use the ARN of the Lambda function in the Resource field.

Depending on the type of integration (Optimized integration or Amazon SDK integration) you use for specifying a Lambda function, the syntax of your Lambda function's Resource field varies.

The following Resource field syntax is an example of an optimized integration with a Lambda function.

"arn:aws-cn:states:::lambda:invoke"

The following Resource field syntax is an example of an Amazon SDK integration with a Lambda function.

"arn:aws-cn:states:::aws-sdk:lambda:invoke"

The following Task state definition shows an example of an optimized integration with a Lambda function named HelloWorld.

"LambdaState": { "Type": "Task", "Resource": "arn:aws-cn:states:::lambda:invoke", "OutputPath": "$.Payload", "Parameters": { "Payload.$": "$", "FunctionName": "arn:aws-cn:lambda:us-east-1:function:HelloWorld:$LATEST" }, "Next": "NextState" }

After the Lambda function specified in the Resource field completes, its output is sent to the state identified in the Next field ("NextState").

A supported Amazon Web Service

When you reference a connected resource, Step Functions directly calls the API actions of a supported service. Specify the service and action in the Resource field.

Connected service Resource ARNs use the following syntax.

arn:partition:states:region:account:servicename:APIname
Note

To create a synchronous connection to a connected resource, append .sync to the APIname entry in the ARN. For more information, see Working with other services.

For example:

{ "StartAt": "BATCH_JOB", "States": { "BATCH_JOB": { "Type": "Task", "Resource": "arn:aws-cn:states:::batch:submitJob.sync", "Parameters": { "JobDefinition": "preprocessing", "JobName": "PreprocessingBatchJob", "JobQueue": "SecondaryQueue", "Parameters.$": "$.batchjob.parameters", "RetryStrategy": { "attempts": 5 } }, "End": true } } }

Task state fields

In addition to the common state fields, Task states have the following fields.

Resource (Required)

A URI, especially an ARN that uniquely identifies the specific task to execute.

Parameters (Optional)

Used to pass information to the API actions of connected resources. The parameters can use a mix of static JSON and JsonPath. For more information, see Pass parameters to a service API.

Credentials (Optional)

Specifies a target role the state machine's execution role must assume before invoking the specified Resource. Alternatively, you can also specify a JSONPath value or an intrinsic function that resolves to an IAM role ARN at runtime based on the execution input. If you specify a JSONPath value, you must prefix it with the $. notation.

For examples of using this field in the Task state, see . For an example of using this field to access a cross-account Amazon resource from your state machine, see Tutorial: Accessing cross-account Amazon resources.

Note

This field is supported by the Task types that use Lambda functions and a supported Amazon service.

ResultPath (Optional)

Specifies where (in the input) to place the results of executing the task that's specified in Resource. The input is then filtered as specified by the OutputPath field (if present) before being used as the state's output. For more information, see Input and Output Processing.

ResultSelector (Optional)

Pass a collection of key value pairs, where the values are static or selected from the result. For more information, see ResultSelector.

Retry (Optional)

An array of objects, called Retriers, that define a retry policy if the state encounters runtime errors. For more information, see State machine examples using Retry and using Catch.

Catch (Optional)

An array of objects, called Catchers, that define a fallback state. This state is executed if the state encounters runtime errors and its retry policy is exhausted or isn't defined. For more information, see Fallback States.

TimeoutSeconds (Optional)

Specifies the maximum time an activity or a task can run before it times out with the States.Timeout error and fails. The timeout value must be positive, non-zero integer. The default value is 99999999.

The timeout count begins after a task starts, for example, when ActivityStarted or LambdaFunctionStarted events are logged in the execution event history. For Activities, the count begins when GetActivityTask receives a token and ActivityStarted is logged in the execution event history.

When a task starts, Step Functions waits for a success or failure response from the task or activity worker within the specified TimeoutSeconds duration. If the task or activity worker fails to respond within this time, Step Functions marks the workflow execution as failed.

TimeoutSecondsPath (Optional)

If you want to provide a timeout value dynamically from the state input using a reference path, use TimeoutSecondsPath. When resolved, the reference path must select fields whose values are positive integers.

Note

A Task state cannot include both TimeoutSeconds and TimeoutSecondsPath.

HeartbeatSeconds (Optional)

Determines the frequency of heartbeat signals an activity worker sends during the execution of a task. Heartbeats indicate that a task is still running and it needs more time to complete. Heartbeats prevent an activity or task from timing out within the TimeoutSeconds duration.

HeartbeatSeconds must be a positive, non-zero integer value less than the TimeoutSeconds field value. The default value is 99999999. If more time than the specified seconds elapses between heartbeats from the task, the Task state fails with a States.Timeout error.

For Activities, the count begins when GetActivityTask receives a token and ActivityStarted is logged in the execution event history.

HeartbeatSecondsPath (Optional)

If you want to provide a heartbeat value dynamically from the state input using a reference path, use HeartbeatSecondsPath. When resolved, the reference path must select fields whose values are positive integers.

Note

A Task state cannot include both HeartbeatSeconds and HeartbeatSecondsPath.

A Task state must set either the End field to true if the state ends the execution, or must provide a state in the Next field that is run when the Task state is complete.

Task state definition examples

The following examples show how you can specify the Task state definition based on your requirement.

Task state timeouts and heartbeat intervals

It's a good practice to set a timeout value and a heartbeat interval for long-running activities. This can be done by specifying the timeout and heartbeat values, or by setting them dynamically.

Static timeout and heartbeat notification example

When HelloWorld completes, the next state (here called NextState) will be run.

If this task fails to complete within 300 seconds, or doesn't send heartbeat notifications in intervals of 60 seconds, the task is marked as failed.

"ActivityState": { "Type": "Task", "Resource": "arn:aws-cn:states:us-east-1:123456789012:activity:HelloWorld", "TimeoutSeconds": 300, "HeartbeatSeconds": 60, "Next": "NextState" }

Dynamic task timeout and heartbeat notification example

In this example, when the Amazon Glue job completes, the next state will be run.

If this task fails to complete within the interval set dynamically by the Amazon Glue job, the task is marked as failed.

"GlueJobTask": { "Type": "Task", "Resource": "arn:aws-cn:states:::glue:startJobRun.sync", "Parameters": { "JobName": "myGlueJob" }, "TimeoutSecondsPath": "$.params.maxTime", "Next": "NextState" }