Invoke Synchronous Express Workflows - AWS Step Functions

Invoke Synchronous Express Workflows

This sample project demonstrates how to invoke Synchronous Express Workflows through Amazon API Gateway to manage an employee database. This sample project creates the following:

  • Three state machines.

  • An Amazon API Gateway HTTPS API that is called by a state machine.

  • An Amazon DynamoDB table.

  • Related AWS Identity and Access Management (IAM) roles

In this project, Step Functions uses API Gateway endpoints to start Step Functions Synchronous Express Workflows. These then use DynamoDB to search for, add, and remove employees in an employee database.

For more information about Step Functions Synchronous Express Workflows, see Synchronous and Asynchronous Express Workflows.

Note

This sample project may incur charges.

For new AWS users, a free usage tier is available. On this tier, services are free below a certain level of usage. For more information about AWS costs and the Free Tier, see Step Functions Pricing.

Create the State Machine and Provision Resources

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

  2. Choose Sample Projects, and then choose Invoke Synchronous Express Workflows through API Gateway.

    The state machine Code and Visual Workflow are displayed.

    
            Training model workflow.
  3. Choose Next.

    The Deploy resources page is displayed, listing the resources that will be created. For this sample project, the resources include:

    • Three state machines

    • A DynamoDB table

    • An API Gateway HTTPS API

    • Related IAM roles

  4. Choose Deploy Resources.

    Note

    It can take up to 10 minutes for these resources and related IAM permissions to be created. While the Deploy resources page is displayed, you can open the Stack ID link to see which resources are being provisioned.

Start a New Execution

  1. Open the Step Functions console.

  2. On the State machines page, choose the state machine that was created by the sample project, and then choose Start execution.

  3. On the New execution page, enter an execution name (optional), and then choose Start Execution.

  4. (Optional) To help identify your execution, you can specify an ID for it in the Enter an execution name box. If you don't enter an ID, Step Functions generates a unique ID automatically.

    Note

    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.

  5. (Optional) Go to the newly created state machine on the Step Functions Dashboard, and then choose New execution.

  6. When an execution is complete, you can select states on the Visual workflow and browse the Input and Output under Step details.

Example State Machine Code

The state machine in this sample project integrates with API Gateway and DynamoDB by using API Gateway to invoke a Synchronous Express Workflow, which then updates or reads from the employee database using DynamoDB.

Browse through this example state machine to see how Step Functions reads from DynamoDB to retrieve employee information.

To understand more about how to invoke Step Functions using API Gateway, see the following.

For more information about how AWS Step Functions can control other AWS services, see Using AWS Step Functions with other services.

{ "Comment": "This state machine returns an employee entry from DynamoDB", "StartAt": "Read From DynamoDB", "States": { "Read From DynamoDB": { "Type": "Task", "Resource": "arn:aws:states:::dynamodb:getItem", "Parameters": { "TableName": "StepFunctionsSample-SynchronousExpressWorkflowAKIAIOSFODNN7EXAMPLE-DynamoDBTable-ANPAJ2UCCR6DPCEXAMPLE", "Key": { "EmployeeId": {"S.$": "$.employee"} } }, "Retry": [ { "ErrorEquals": [ "DynamoDB.AmazonDynamoDBException" ], "IntervalSeconds": 3, "MaxAttempts": 2, "BackoffRate": 1.5 } ], "Next": "Is Get Successful" }, "Is Get Successful": { "Type": "Choice", "Choices": [ { "Variable": "$.Item", "IsPresent": true, "Next": "Succeed Execution" } ], "Default": "Fail Execution" }, "Succeed Execution": { "Type": "Pass", "Parameters" : { "employee.$": "$.Item.EmployeeId.S", "jobTitle.$": "$.Item.JobTitle.S" }, "End": true }, "Fail Execution": { "Type": "Fail", "Error": "EmployeeDoesNotExist" } } }

For information about how to configure IAM when using Step Functions with other AWS services, see IAM Policies for Integrated Services.

IAM Examples

These example AWS Identity and Access Management (IAM) policies generated by the sample project include the least privilege necessary to execute the state machine and related resources. We recommend that you include only those permissions that are necessary in your IAM policies.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "logs:CreateLogDelivery", "logs:GetLogDelivery", "logs:UpdateLogDelivery", "logs:DeleteLogDelivery", "logs:ListLogDeliveries", "logs:PutResourcePolicy", "logs:DescribeResourcePolicies", "logs:DescribeLogGroups" ], "Resource": "*" } ] }
{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "dynamodb:GetItem", "dynamodb:PutItem", "dynamodb:UpdateItem", "dynamodb:DeleteItem" ], "Resource": [ "arn:aws:dynamodb:us-east-1:111122223333:table/Write" ] } ] }

For information about how to configure IAM when using Step Functions with other AWS services, see IAM Policies for Integrated Services.