Tasks for AWS Step Functions¶

---

cdk-constructs: Stable

AWS Step Functions is a web service that enables you to coordinate the components of distributed applications and microservices using visual workflows. You build applications from individual components that each perform a discrete function, or task, allowing you to scale and change applications quickly.

A Task state represents a single unit of work performed by a state machine. All work in your state machine is performed by tasks.

This module is part of the AWS Cloud Development Kit project.

Table Of Contents¶

Task¶

A Task state represents a single unit of work performed by a state machine. In the CDK, the exact work to be done is determined by a class that implements IStepFunctionsTask.

AWS Step Functions integrates with some AWS services so that you can call API actions, and coordinate executions directly from the Amazon States Language in Step Functions. You can directly call and pass parameters to the APIs of those services.

Paths¶

In the Amazon States Language, a path is a string beginning with $ that you can use to identify components within JSON text.

Learn more about input and output processing in Step Functions here

InputPath¶

Both InputPath and Parameters fields provide a way to manipulate JSON as it moves through your workflow. AWS Step Functions applies the InputPath field first, and then the Parameters field. You can first filter your raw input to a selection you want using InputPath, and then apply Parameters to manipulate that input further, or add new values. If you don’t specify an InputPath, a default value of $ will be used.

The following example provides the field named input as the input to the Task state that runs a Lambda function.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
submit_job = tasks.LambdaInvoke(self, "Invoke Handler",
    lambda_function=fn,
    input_path="$.input"
)

OutputPath¶

Tasks also allow you to select a portion of the state output to pass to the next state. This enables you to filter out unwanted information, and pass only the portion of the JSON that you care about. If you don’t specify an OutputPath, a default value of $ will be used. This passes the entire JSON node to the next state.

The response from a Lambda function includes the response from the function as well as other metadata.

The following example assigns the output from the Task to a field named result

# Example automatically generated. See https://github.com/aws/jsii/issues/826
submit_job = tasks.LambdaInvoke(self, "Invoke Handler",
    lambda_function=fn,
    output_path="$.Payload.result"
)

ResultSelector¶

You can use ResultSelector to manipulate the raw result of a Task, Map or Parallel state before it is passed to ResultPath. For service integrations, the raw result contains metadata in addition to the response payload. You can use ResultSelector to construct a JSON payload that becomes the effective result using static values or references to the raw result or context object.

The following example extracts the output payload of a Lambda function Task and combines it with some static values and the state name from the context object.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke Handler",
    lambda_function=fn,
    result_selector={
        "lambda_output": sfn.JsonPath.string_at("$.Payload"),
        "invoke_request_id": sfn.JsonPath.string_at("$.SdkResponseMetadata.RequestId"),
        "static_value": {
            "foo": "bar"
        },
        "state_name": sfn.JsonPath.string_at("$.State.Name")
    }
)

ResultPath¶

The output of a state can be a copy of its input, the result it produces (for example, output from a Task state’s Lambda function), or a combination of its input and result. Use ResultPath to control which combination of these is passed to the state output. If you don’t specify an ResultPath, a default value of $ will be used.

The following example adds the item from calling DynamoDB’s getItem API to the state input and passes it to the next state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.DynamoPutItem(self, "PutItem",
    item={
        "MessageId": tasks.DynamoAttributeValue.from_string("message-id")
    },
    table=my_table,
    result_path="$.Item"
)

⚠️ The OutputPath is computed after applying ResultPath. All service integrations return metadata as part of their response. When using ResultPath, it’s not possible to merge a subset of the task output to the input.

Task parameters from the state JSON¶

Most tasks take parameters. Parameter values can either be static, supplied directly in the workflow definition (by specifying their values), or a value available at runtime in the state machine’s execution (either as its input or an output of a prior state). Parameter values available at runtime can be specified via the JsonPath class, using methods such as JsonPath.stringAt().

The following example provides the field named input as the input to the Lambda function and invokes it asynchronously.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
submit_job = tasks.LambdaInvoke(self, "Invoke Handler",
    lambda_function=fn,
    payload=sfn.TaskInput.from_json_path_at("$.input"),
    invocation_type=tasks.LambdaInvocationType.EVENT
)

You can also use intrinsic functions with JsonPath.stringAt(). Here is an example of starting an Athena query that is dynamically created using the task input:

# Example automatically generated. See https://github.com/aws/jsii/issues/826
start_query_execution_job = tasks.AthenaStartQueryExecution(self, "Athena Start Query",
    query_string=sfn.JsonPath.string_at("States.Format('select contacts where year={};', $.year)"),
    query_execution_context={
        "database_name": "interactions"
    },
    result_configuration={
        "encryption_configuration": {
            "encryption_option": tasks.EncryptionOption.S3_MANAGED
        },
        "output_location": {
            "bucket_name": "mybucket",
            "object_key": "myprefix"
        }
    },
    integration_pattern=sfn.IntegrationPattern.RUN_JOB
)

Each service integration has its own set of parameters that can be supplied.

Evaluate Expression¶

Use the EvaluateExpression to perform simple operations referencing state paths. The expression referenced in the task will be evaluated in a Lambda function (eval()). This allows you to not have to write Lambda code for simple operations.

Example: convert a wait time from milliseconds to seconds, concat this in a message and wait:

# Example automatically generated. See https://github.com/aws/jsii/issues/826
convert_to_seconds = tasks.EvaluateExpression(self, "Convert to seconds",
    expression="$.waitMilliseconds / 1000",
    result_path="$.waitSeconds"
)

create_message = tasks.EvaluateExpression(self, "Create message",
    # Note: this is a string inside a string.
    expression="`Now waiting ${$.waitSeconds} seconds...`",
    runtime=lambda_.Runtime.NODEJS_14_X,
    result_path="$.message"
)

publish_message = tasks.SnsPublish(self, "Publish message",
    topic=sns.Topic(self, "cool-topic"),
    message=sfn.TaskInput.from_json_path_at("$.message"),
    result_path="$.sns"
)

wait = sfn.Wait(self, "Wait",
    time=sfn.WaitTime.seconds_path("$.waitSeconds")
)

sfn.StateMachine(self, "StateMachine",
    definition=convert_to_seconds.next(create_message).next(publish_message).next(wait)
)

The EvaluateExpression supports a runtime prop to specify the Lambda runtime to use to evaluate the expression. Currently, only runtimes of the Node.js family are supported.

API Gateway¶

Step Functions supports API Gateway through the service integration pattern.

HTTP APIs are designed for low-latency, cost-effective integrations with AWS services, including AWS Lambda, and HTTP endpoints. HTTP APIs support OIDC and OAuth 2.0 authorization, and come with built-in support for CORS and automatic deployments. Previous-generation REST APIs currently offer more features. More details can be found here.

Call REST API Endpoint¶

The CallApiGatewayRestApiEndpoint calls the REST API endpoint.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_stepfunctions as sfn
import ??? as tasks


rest_api = apigateway.RestApi(stack, "MyRestApi")

invoke_task = tasks.CallApiGatewayRestApiEndpoint(stack, "Call REST API",
    api=rest_api,
    stage_name="prod",
    method=HttpMethod.GET
)

Call HTTP API Endpoint¶

The CallApiGatewayHttpApiEndpoint calls the HTTP API endpoint.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_stepfunctions as sfn
import ??? as tasks


http_api = apigatewayv2.HttpApi(stack, "MyHttpApi")

invoke_task = tasks.CallApiGatewayHttpApiEndpoint(stack, "Call HTTP API",
    api_id=http_api.api_id,
    api_stack=cdk.Stack.of(http_api),
    method=HttpMethod.GET
)

AWS SDK¶

Step Functions supports calling AWS service’s API actions through the service integration pattern.

You can use Step Functions’ AWS SDK integrations to call any of the over two hundred AWS services directly from your state machine, giving you access to over nine thousand API actions.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
get_object = tasks.CallAwsService(self, "GetObject",
    service="s3",
    action="getObject",
    parameters={
        "Bucket": my_bucket.bucket_name,
        "Key": sfn.JsonPath.string_at("$.key")
    },
    iam_resources=[my_bucket.arn_for_objects("*")]
)

Use camelCase for actions and PascalCase for parameter names.

The task automatically adds an IAM statement to the state machine role’s policy based on the service and action called. The resources for this statement must be specified in iamResources.

Use the iamAction prop to manually specify the IAM action name in the case where the IAM action name does not match with the API service/action name:

# Example automatically generated. See https://github.com/aws/jsii/issues/826
list_buckets = tasks.CallAwsService(self, "ListBuckets",
    service="s3",
    action="ListBuckets",
    iam_resources=["*"],
    iam_action="s3:ListAllMyBuckets"
)

Athena¶

Step Functions supports Athena through the service integration pattern.

StartQueryExecution¶

The StartQueryExecution API runs the SQL query statement.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
start_query_execution_job = tasks.AthenaStartQueryExecution(self, "Start Athena Query",
    query_string=sfn.JsonPath.string_at("$.queryString"),
    query_execution_context={
        "database_name": "mydatabase"
    },
    result_configuration={
        "encryption_configuration": {
            "encryption_option": tasks.EncryptionOption.S3_MANAGED
        },
        "output_location": {
            "bucket_name": "query-results-bucket",
            "object_key": "folder"
        }
    }
)

GetQueryExecution¶

The GetQueryExecution API gets information about a single execution of a query.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
get_query_execution_job = tasks.AthenaGetQueryExecution(self, "Get Query Execution",
    query_execution_id=sfn.JsonPath.string_at("$.QueryExecutionId")
)

GetQueryResults¶

The GetQueryResults API that streams the results of a single query execution specified by QueryExecutionId from S3.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
get_query_results_job = tasks.AthenaGetQueryResults(self, "Get Query Results",
    query_execution_id=sfn.JsonPath.string_at("$.QueryExecutionId")
)

StopQueryExecution¶

The StopQueryExecution API that stops a query execution.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
stop_query_execution_job = tasks.AthenaStopQueryExecution(self, "Stop Query Execution",
    query_execution_id=sfn.JsonPath.string_at("$.QueryExecutionId")
)

Batch¶

Step Functions supports Batch through the service integration pattern.

SubmitJob¶

The SubmitJob API submits an AWS Batch job from a job definition.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
task = tasks.BatchSubmitJob(self, "Submit Job",
    job_definition_arn=batch_job_definition_arn,
    job_name="MyJob",
    job_queue_arn=batch_queue_arn
)

CodeBuild¶

Step Functions supports CodeBuild through the service integration pattern.

StartBuild¶

StartBuild starts a CodeBuild Project by Project Name.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_codebuild as codebuild


codebuild_project = codebuild.Project(self, "Project",
    project_name="MyTestProject",
    build_spec=codebuild.BuildSpec.from_object({
        "version": "0.2",
        "phases": {
            "build": {
                "commands": ["echo "Hello, CodeBuild!""
                ]
            }
        }
    })
)

task = tasks.CodeBuildStartBuild(self, "Task",
    project=codebuild_project,
    integration_pattern=sfn.IntegrationPattern.RUN_JOB,
    environment_variables_override={
        "ZONE": BuildEnvironmentVariable(
            type=codebuild.BuildEnvironmentVariableType.PLAINTEXT,
            value=sfn.JsonPath.string_at("$.envVariables.zone")
        )
    }
)

DynamoDB¶

You can call DynamoDB APIs from a Task state. Read more about calling DynamoDB APIs here

GetItem¶

The GetItem operation returns a set of attributes for the item with the given primary key.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.DynamoGetItem(self, "Get Item",
    key={"message_id": tasks.DynamoAttributeValue.from_string("message-007")},
    table=my_table
)

PutItem¶

The PutItem operation creates a new item, or replaces an old item with a new item.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.DynamoPutItem(self, "PutItem",
    item={
        "MessageId": tasks.DynamoAttributeValue.from_string("message-007"),
        "Text": tasks.DynamoAttributeValue.from_string(sfn.JsonPath.string_at("$.bar")),
        "TotalCount": tasks.DynamoAttributeValue.from_number(10)
    },
    table=my_table
)

DeleteItem¶

The DeleteItem operation deletes a single item in a table by primary key.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.DynamoDeleteItem(self, "DeleteItem",
    key={"MessageId": tasks.DynamoAttributeValue.from_string("message-007")},
    table=my_table,
    result_path=sfn.JsonPath.DISCARD
)

UpdateItem¶

The UpdateItem operation edits an existing item’s attributes, or adds a new item to the table if it does not already exist.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.DynamoUpdateItem(self, "UpdateItem",
    key={
        "MessageId": tasks.DynamoAttributeValue.from_string("message-007")
    },
    table=my_table,
    expression_attribute_values={
        ":val": tasks.DynamoAttributeValue.number_from_string(sfn.JsonPath.string_at("$.Item.TotalCount.N")),
        ":rand": tasks.DynamoAttributeValue.from_number(20)
    },
    update_expression="SET TotalCount = :val + :rand"
)

ECS¶

Step Functions supports ECS/Fargate through the service integration pattern.

RunTask¶

RunTask starts a new task using the specified task definition.

EC2¶

The EC2 launch type allows you to run your containerized applications on a cluster of Amazon EC2 instances that you manage.

When a task that uses the EC2 launch type is launched, Amazon ECS must determine where to place the task based on the requirements specified in the task definition, such as CPU and memory. Similarly, when you scale down the task count, Amazon ECS must determine which tasks to terminate. You can apply task placement strategies and constraints to customize how Amazon ECS places and terminates tasks. Learn more about task placement

The latest ACTIVE revision of the passed task definition is used for running the task.

The following example runs a job from a task definition on EC2

# Example automatically generated. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_ecs as ecs


vpc = ec2.Vpc.from_lookup(self, "Vpc",
    is_default=True
)

cluster = ecs.Cluster(self, "Ec2Cluster", vpc=vpc)
cluster.add_capacity("DefaultAutoScalingGroup",
    instance_type=ec2.InstanceType("t2.micro"),
    vpc_subnets=SubnetSelection(subnet_type=ec2.SubnetType.PUBLIC)
)

task_definition = ecs.TaskDefinition(self, "TD",
    compatibility=ecs.Compatibility.EC2
)

task_definition.add_container("TheContainer",
    image=ecs.ContainerImage.from_registry("foo/bar"),
    memory_limit_mi_b=256
)

run_task = tasks.EcsRunTask(self, "Run",
    integration_pattern=sfn.IntegrationPattern.RUN_JOB,
    cluster=cluster,
    task_definition=task_definition,
    launch_target=tasks.EcsEc2LaunchTarget(
        placement_strategies=[
            ecs.PlacementStrategy.spread_across_instances(),
            ecs.PlacementStrategy.packed_by_cpu(),
            ecs.PlacementStrategy.randomly()
        ],
        placement_constraints=[
            ecs.PlacementConstraint.member_of("blieptuut")
        ]
    )
)

Fargate¶

AWS Fargate is a serverless compute engine for containers that works with Amazon Elastic Container Service (ECS). Fargate makes it easy for you to focus on building your applications. Fargate removes the need to provision and manage servers, lets you specify and pay for resources per application, and improves security through application isolation by design. Learn more about Fargate

The Fargate launch type allows you to run your containerized applications without the need to provision and manage the backend infrastructure. Just register your task definition and Fargate launches the container for you. The latest ACTIVE revision of the passed task definition is used for running the task. Learn more about Fargate Versioning

The following example runs a job from a task definition on Fargate

# Example automatically generated. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_ecs as ecs


vpc = ec2.Vpc.from_lookup(self, "Vpc",
    is_default=True
)

cluster = ecs.Cluster(self, "FargateCluster", vpc=vpc)

task_definition = ecs.TaskDefinition(self, "TD",
    memory_mi_b="512",
    cpu="256",
    compatibility=ecs.Compatibility.FARGATE
)

container_definition = task_definition.add_container("TheContainer",
    image=ecs.ContainerImage.from_registry("foo/bar"),
    memory_limit_mi_b=256
)

run_task = tasks.EcsRunTask(self, "RunFargate",
    integration_pattern=sfn.IntegrationPattern.RUN_JOB,
    cluster=cluster,
    task_definition=task_definition,
    assign_public_ip=True,
    container_overrides=[ContainerOverride(
        container_definition=container_definition,
        environment=[TaskEnvironmentVariable(name="SOME_KEY", value=sfn.JsonPath.string_at("$.SomeKey"))]
    )],
    launch_target=tasks.EcsFargateLaunchTarget()
)

EMR¶

Step Functions supports Amazon EMR through the service integration pattern. The service integration APIs correspond to Amazon EMR APIs but differ in the parameters that are used.

Read more about the differences when using these service integrations.

Create Cluster¶

Creates and starts running a cluster (job flow). Corresponds to the runJobFlow API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
cluster_role = iam.Role(self, "ClusterRole",
    assumed_by=iam.ServicePrincipal("ec2.amazonaws.com")
)

service_role = iam.Role(self, "ServiceRole",
    assumed_by=iam.ServicePrincipal("elasticmapreduce.amazonaws.com")
)

auto_scaling_role = iam.Role(self, "AutoScalingRole",
    assumed_by=iam.ServicePrincipal("elasticmapreduce.amazonaws.com")
)

auto_scaling_role.assume_role_policy.add_statements(
    iam.PolicyStatement(
        effect=iam.Effect.ALLOW,
        principals=[
            iam.ServicePrincipal("application-autoscaling.amazonaws.com")
        ],
        actions=["sts:AssumeRole"
        ]
    ))

tasks.EmrCreateCluster(self, "Create Cluster",
    instances={},
    cluster_role=cluster_role,
    name=sfn.TaskInput.from_json_path_at("$.ClusterName").value,
    service_role=service_role,
    auto_scaling_role=auto_scaling_role
)

If you want to run multiple steps in parallel, you can specify the stepConcurrencyLevel property. The concurrency range is between 1 and 256 inclusive, where the default concurrency of 1 means no step concurrency is allowed. stepConcurrencyLevel requires the EMR release label to be 5.28.0 or above.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
tasks.EmrCreateCluster(self, "Create Cluster",
    # ...
    step_concurrency_level=10
)

Termination Protection¶

Locks a cluster (job flow) so the EC2 instances in the cluster cannot be terminated by user intervention, an API call, or a job-flow error.

Corresponds to the setTerminationProtection API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrSetClusterTerminationProtection(self, "Task",
    cluster_id="ClusterId",
    termination_protected=False
)

Terminate Cluster¶

Shuts down a cluster (job flow). Corresponds to the terminateJobFlows API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrTerminateCluster(self, "Task",
    cluster_id="ClusterId"
)

Add Step¶

Adds a new step to a running cluster. Corresponds to the addJobFlowSteps API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrAddStep(self, "Task",
    cluster_id="ClusterId",
    name="StepName",
    jar="Jar",
    action_on_failure=tasks.ActionOnFailure.CONTINUE
)

Cancel Step¶

Cancels a pending step in a running cluster. Corresponds to the cancelSteps API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrCancelStep(self, "Task",
    cluster_id="ClusterId",
    step_id="StepId"
)

Modify Instance Fleet¶

Modifies the target On-Demand and target Spot capacities for the instance fleet with the specified InstanceFleetName.

Corresponds to the modifyInstanceFleet API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrModifyInstanceFleetByName(self, "Task",
    cluster_id="ClusterId",
    instance_fleet_name="InstanceFleetName",
    target_on_demand_capacity=2,
    target_spot_capacity=0
)

Modify Instance Group¶

Modifies the number of nodes and configuration settings of an instance group.

Corresponds to the modifyInstanceGroups API in EMR.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.EmrModifyInstanceGroupByName(self, "Task",
    cluster_id="ClusterId",
    instance_group_name=sfn.JsonPath.string_at("$.InstanceGroupName"),
    instance_group={
        "instance_count": 1
    }
)

EKS¶

Step Functions supports Amazon EKS through the service integration pattern. The service integration APIs correspond to Amazon EKS APIs.

Read more about the differences when using these service integrations.

Call¶

Read and write Kubernetes resource objects via a Kubernetes API endpoint. Corresponds to the call API in Step Functions Connector.

The following code snippet includes a Task state that uses eks:call to list the pods.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_eks as eks
import aws_cdk.aws_stepfunctions as sfn
import aws_cdk.aws_stepfunctions_tasks as tasks


my_eks_cluster = eks.Cluster(self, "my sample cluster",
    version=eks.KubernetesVersion.V1_18,
    cluster_name="myEksCluster"
)

tasks.EksCall(stack, "Call a EKS Endpoint",
    cluster=my_eks_cluster,
    http_method=MethodType.GET,
    http_path="/api/v1/namespaces/default/pods"
)

EventBridge¶

Step Functions supports Amazon EventBridge through the service integration pattern. The service integration APIs correspond to Amazon EventBridge APIs.

Read more about the differences when using these service integrations.

Put Events¶

Send events to an EventBridge bus. Corresponds to the put-events API in Step Functions Connector.

The following code snippet includes a Task state that uses events:putevents to send an event to the default bus.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
import aws_cdk.aws_events as events
import aws_cdk.aws_stepfunctions as sfn
import aws_cdk.aws_stepfunctions_tasks as tasks


my_event_bus = events.EventBus(stack, "EventBus",
    event_bus_name="MyEventBus1"
)

tasks.EventBridgePutEvents(stack, "Send an event to EventBridge",
    entries=[EventBridgePutEventsEntry(
        detail=sfn.TaskInput.from_object({
            "Message": "Hello from Step Functions!"
        }),
        event_bus=my_event_bus,
        detail_type="MessageFromStepFunctions",
        source="step.functions"
    )]
)

Glue¶

Step Functions supports AWS Glue through the service integration pattern.

You can call the StartJobRun API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.GlueStartJobRun(self, "Task",
    glue_job_name="my-glue-job",
    arguments=sfn.TaskInput.from_object(
        key="value"
    ),
    timeout=cdk.Duration.minutes(30),
    notify_delay_after=cdk.Duration.minutes(5)
)

Glue DataBrew¶

Step Functions supports AWS Glue DataBrew through the service integration pattern.

You can call the StartJobRun API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.GlueDataBrewStartJobRun(self, "Task",
    name="databrew-job"
)

Lambda¶

Invoke a Lambda function.

You can specify the input to your Lambda function through the payload attribute. By default, Step Functions invokes Lambda function with the state input (JSON path ‘$’) as the input.

The following snippet invokes a Lambda Function with the state input as the payload by referencing the $ path.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke with state input",
    lambda_function=fn
)

When a function is invoked, the Lambda service sends these response elements back.

⚠️ The response from the Lambda function is in an attribute called Payload

The following snippet invokes a Lambda Function by referencing the $.Payload path to reference the output of a Lambda executed before it.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke with empty object as payload",
    lambda_function=fn,
    payload=sfn.TaskInput.from_object()
)

# use the output of fn as input
tasks.LambdaInvoke(self, "Invoke with payload field in the state input",
    lambda_function=fn,
    payload=sfn.TaskInput.from_json_path_at("$.Payload")
)

The following snippet invokes a Lambda and sets the task output to only include the Lambda function response.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke and set function response as task output",
    lambda_function=fn,
    output_path="$.Payload"
)

If you want to combine the input and the Lambda function response you can use the payloadResponseOnly property and specify the resultPath. This will put the Lambda function ARN directly in the “Resource” string, but it conflicts with the integrationPattern, invocationType, clientContext, and qualifier properties.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke and combine function response with task input",
    lambda_function=fn,
    payload_response_only=True,
    result_path="$.fn"
)

You can have Step Functions pause a task, and wait for an external process to return a task token. Read more about the callback pattern

To use the callback pattern, set the token property on the task. Call the Step Functions SendTaskSuccess or SendTaskFailure APIs with the token to indicate that the task has completed and the state machine should resume execution.

The following snippet invokes a Lambda with the task token as part of the input to the Lambda.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.LambdaInvoke(self, "Invoke with callback",
    lambda_function=fn,
    integration_pattern=sfn.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
    payload=sfn.TaskInput.from_object(
        token=sfn.JsonPath.task_token,
        input=sfn.JsonPath.string_at("$.someField")
    )
)

⚠️ The task will pause until it receives that task token back with a SendTaskSuccess or SendTaskFailure call. Learn more about Callback with the Task Token.

AWS Lambda can occasionally experience transient service errors. In this case, invoking Lambda results in a 500 error, such as ServiceException, AWSLambdaException, or SdkClientException. As a best practice, the LambdaInvoke task will retry on those errors with an interval of 2 seconds, a back-off rate of 2 and 6 maximum attempts. Set the retryOnServiceExceptions prop to false to disable this behavior.

SageMaker¶

Step Functions supports AWS SageMaker through the service integration pattern.

If your training job or model uses resources from AWS Marketplace, network isolation is required. To do so, set the enableNetworkIsolation property to true for SageMakerCreateModel or SageMakerCreateTrainingJob.

Create Training Job¶

You can call the CreateTrainingJob API from a Task state.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
tasks.SageMakerCreateTrainingJob(self, "TrainSagemaker",
    training_job_name=sfn.JsonPath.string_at("$.JobName"),
    algorithm_specification={
        "algorithm_name": "BlazingText",
        "training_input_mode": tasks.InputMode.FILE
    },
    input_data_config=[{
        "channel_name": "train",
        "data_source": {
            "s3_data_source": {
                "s3_data_type": tasks.S3DataType.S3_PREFIX,
                "s3_location": tasks.S3Location.from_json_expression("$.S3Bucket")
            }
        }
    }],
    output_data_config={
        "s3_output_location": tasks.S3Location.from_bucket(s3.Bucket.from_bucket_name(self, "Bucket", "mybucket"), "myoutputpath")
    },
    resource_config={
        "instance_count": 1,
        "instance_type": ec2.InstanceType(JsonPath.string_at("$.InstanceType")),
        "volume_size": cdk.Size.gibibytes(50)
    },  # optional: default is 1 instance of EC2 `M4.XLarge` with `10GB` volume
    stopping_condition={
        "max_runtime": cdk.Duration.hours(2)
    }
)

Create Transform Job¶

You can call the CreateTransformJob API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.SageMakerCreateTransformJob(self, "Batch Inference",
    transform_job_name="MyTransformJob",
    model_name="MyModelName",
    model_client_options={
        "invocations_max_retries": 3,  # default is 0
        "invocations_timeout": cdk.Duration.minutes(5)
    },
    transform_input={
        "transform_data_source": {
            "s3_data_source": {
                "s3_uri": "s3://inputbucket/train",
                "s3_data_type": tasks.S3DataType.S3_PREFIX
            }
        }
    },
    transform_output={
        "s3_output_path": "s3://outputbucket/TransformJobOutputPath"
    },
    transform_resources={
        "instance_count": 1,
        "instance_type": ec2.InstanceType.of(ec2.InstanceClass.M4, ec2.InstanceSize.XLARGE)
    }
)

Create Endpoint¶

You can call the CreateEndpoint API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.SageMakerCreateEndpoint(self, "SagemakerEndpoint",
    endpoint_name=sfn.JsonPath.string_at("$.EndpointName"),
    endpoint_config_name=sfn.JsonPath.string_at("$.EndpointConfigName")
)

Create Endpoint Config¶

You can call the CreateEndpointConfig API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.SageMakerCreateEndpointConfig(self, "SagemakerEndpointConfig",
    endpoint_config_name="MyEndpointConfig",
    production_variants=[{
        "initial_instance_count": 2,
        "instance_type": ec2.InstanceType.of(ec2.InstanceClass.M5, ec2.InstanceSize.XLARGE),
        "model_name": "MyModel",
        "variant_name": "awesome-variant"
    }]
)

Create Model¶

You can call the CreateModel API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.SageMakerCreateModel(self, "Sagemaker",
    model_name="MyModel",
    primary_container=tasks.ContainerDefinition(
        image=tasks.DockerImage.from_json_expression(sfn.JsonPath.string_at("$.Model.imageName")),
        mode=tasks.Mode.SINGLE_MODEL,
        model_s3_location=tasks.S3Location.from_json_expression("$.TrainingJob.ModelArtifacts.S3ModelArtifacts")
    )
)

Update Endpoint¶

You can call the UpdateEndpoint API from a Task state.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
tasks.SageMakerUpdateEndpoint(self, "SagemakerEndpoint",
    endpoint_name=sfn.JsonPath.string_at("$.Endpoint.Name"),
    endpoint_config_name=sfn.JsonPath.string_at("$.Endpoint.EndpointConfig")
)

SNS¶

Step Functions supports Amazon SNS through the service integration pattern.

You can call the Publish API from a Task state to publish to an SNS topic.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
topic = sns.Topic(self, "Topic")

# Use a field from the execution data as message.
task1 = tasks.SnsPublish(self, "Publish1",
    topic=topic,
    integration_pattern=sfn.IntegrationPattern.REQUEST_RESPONSE,
    message=sfn.TaskInput.from_data_at("$.state.message"),
    message_attributes={
        "place": {
            "value": sfn.JsonPath.string_at("$.place")
        },
        "pic": {
            # BINARY must be explicitly set
            "type": MessageAttributeDataType.BINARY,
            "value": sfn.JsonPath.string_at("$.pic")
        },
        "people": {
            "value": 4
        },
        "handles": {
            "value": ["@kslater", "@jjf", null, "@mfanning"]
        }
    }
)

# Combine a field from the execution data with
# a literal object.
task2 = tasks.SnsPublish(self, "Publish2",
    topic=topic,
    message=sfn.TaskInput.from_object(
        field1="somedata",
        field2=sfn.JsonPath.string_at("$.field2")
    )
)

Step Functions¶

Start Execution¶

You can manage AWS Step Functions executions.

AWS Step Functions supports it’s own StartExecution API as a service integration.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
# Define a state machine with one Pass state
child = sfn.StateMachine(self, "ChildStateMachine",
    definition=sfn.Chain.start(sfn.Pass(self, "PassState"))
)

# Include the state machine in a Task state with callback pattern
task = tasks.StepFunctionsStartExecution(self, "ChildTask",
    state_machine=child,
    integration_pattern=sfn.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
    input=sfn.TaskInput.from_object(
        token=sfn.JsonPath.task_token,
        foo="bar"
    ),
    name="MyExecutionName"
)

# Define a second state machine with the Task state above
sfn.StateMachine(self, "ParentStateMachine",
    definition=task
)

You can utilize Associate Workflow Executions via the associateWithParent property. This allows the Step Functions UI to link child executions from parent executions, making it easier to trace execution flow across state machines.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
task = tasks.StepFunctionsStartExecution(self, "ChildTask",
    state_machine=child,
    associate_with_parent=True
)

This will add the payload AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID.$: $$.Execution.Id to the inputproperty for you, which will pass the execution ID from the context object to the execution input. It requires input to be an object or not be set at all.

Invoke Activity¶

You can invoke a Step Functions Activity which enables you to have a task in your state machine where the work is performed by a worker that can be hosted on Amazon EC2, Amazon ECS, AWS Lambda, basically anywhere. Activities are a way to associate code running somewhere (known as an activity worker) with a specific task in a state machine.

When Step Functions reaches an activity task state, the workflow waits for an activity worker to poll for a task. An activity worker polls Step Functions by using GetActivityTask, and sending the ARN for the related activity.

After the activity worker completes its work, it can provide a report of its success or failure by using SendTaskSuccess or SendTaskFailure. These two calls use the taskToken provided by GetActivityTask to associate the result with that task.

The following example creates an activity and creates a task that invokes the activity.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
submit_job_activity = sfn.Activity(self, "SubmitJob")

tasks.StepFunctionsInvokeActivity(self, "Submit Job",
    activity=submit_job_activity
)

SQS¶

Step Functions supports Amazon SQS

You can call the SendMessage API from a Task state to send a message to an SQS queue.

# Example automatically generated. See https://github.com/aws/jsii/issues/826
queue = sqs.Queue(self, "Queue")

# Use a field from the execution data as message.
task1 = tasks.SqsSendMessage(self, "Send1",
    queue=queue,
    message_body=sfn.TaskInput.from_json_path_at("$.message")
)

# Combine a field from the execution data with
# a literal object.
task2 = tasks.SqsSendMessage(self, "Send2",
    queue=queue,
    message_body=sfn.TaskInput.from_object(
        field1="somedata",
        field2=sfn.JsonPath.string_at("$.field2")
    )
)