Add conditional logic to your Step Functions workflow

1. Open the Amazon SNS console and create a Standard topic type. For information about creating a topic, see Create an Amazon SNS topic in the Amazon Simple Notification Service Developer Guide.

2. Specify the topic name as TaskTokenTopic.

3. Make sure to copy the topic ARN and save it in a text file. You’ll need the topic ARN while specifying the service integration for the Wait for human approval state. The following is an example topic ARN:

   arn:aws-cn:sns:us-west-2:123456789012:TaskTokenTopic

4. Create an email-based subscription for the topic and then confirm your subscription. For information about subscribing to a topic, see Create a subscription to the topic in the Amazon Simple Notification Service Developer Guide.

1. In a new tab or window, open the Lambda console and create a Node.js Lambda function titled callback-human-approval. For information about creating a Lambda function using the console, see Create a Lambda function in the console in the Amazon Lambda Developer Guide.

2. On the callback-human-approval page, replace the existing code in the Code source area with the following code.

   // Lambda function that will automatically approve any task 
   // in a message published to an Amazon SNS topic
   
   console.log('Loading function');
   const AWS = require('aws-sdk');
   const resultMessage = "Successful";
   
   export const handler = async (event) => {
       const stepfunctions = new AWS.StepFunctions();
       
       let message = JSON.parse(event.Records[0].Sns.Message);
       let taskToken = message.TaskToken;
       
       console.log('Message received from SNS:', message); 
       console.log('Task token: ', taskToken);
       
       // Return task token to Step Functions
       
       let params = {
           output: JSON.stringify(resultMessage),
           taskToken: taskToken
       };
       
       console.log('JSON Returned to Step Functions: ', params);
       let myResult = await stepfunctions.sendTaskSuccess(params).promise();
       console.log('State machine - callback completed..');
       
       return myResult;
       
   };

3. Keep this window open and perform the steps in the next section for further actions.

1. In the Function overview section of the callback-human-approval Lambda function, choose Add trigger.

2. From the drop-down list of triggers, choose SNS as the trigger.

3. For SNS topic, start typing the name of the Amazon SNS topic you created in Step 1 of this tutorial, and choose it from the dropdown list that appears.

4. Choose Add.

5. Keep this window open and perform the steps in the next section for further actions.

1. On the callback-human-approval page, choose the Configuration tab, and then choose Permissions.

2. Under Execution role, choose the Role name to navigate to the Amazon Identity and Access Management console’s Roles page.

3. To add the required permission, choose Add permissions, and then choose Attach policies.

4. In the search box, type AWSStepFunctions and then press Enter.

5. Choose AWSStepFunctionsFullAccess and then scroll down to choose Attach policies. This adds the policy containing the necessary permission for the callback-human-approval Lambda function role.

To add if-else condition logic using the Choice state

1. Open the Step Functions console window containing the workflow prototype you created in Create a state machine.

2. Choose the Credit applied >= 5000? state and in the Configuration tab, specify the conditional logic as follows:

   1. Under Choice Rules, choose the Edit icon in the Rule #1 tile to define the first choice rule.

   2. Choose Add conditions.

   3. In the Conditions for rule #1 dialog box, for Variable, enter $.

   4. For Operator, choose is less than.

   5. For Value, choose Number constant, and then enter 5000 in the field next to the Value dropdown list.

   6. Choose Save conditions.

   7. For the Then next state is: dropdown list, choose Auto-approve limit.

   8. Choose Add new choice rule, and then define the second choice rule when the credit amount is greater than or equal to 5000 by repeating substeps 2.b through 2.f. For Operator, choose is greater than or equal to.

   9. For the Then next state is: dropdown list, choose Wait for human approval.

   10. In the Default rule box, choose the Edit icon to define the default choice rule, and then choose Wait for human approval from the Default state dropdown list. You define the Default rule to specify the next state to transition to if none of the Choice state conditions evaluate to true or false.

3. Configure the Wait for human approval state as follows:

   1. In the Configuration tab, for Topic, start typing the name of the Amazon SNS topic, TaskTokenTopic, and choose the name as it appears in the dropdown list.

   2. For Message, choose Enter message from the dropdown list. In the Message field, you specify the message you want to publish to the Amazon SNS topic. For this tutorial, you publish a task token as the message.

      A task token lets you pause a Standard type Step Functions workflow until an external process is complete and the task token is returned. When you specify a Task state as a callback task by specifying the .waitForTaskToken service integration pattern, a task token is generated and placed in the Context object when the task is started. The Context object is an internal JSON structure that is available during an execution, and contains information about your state machine and its execution. For more information about Context objects, see Accessing execution data from the Context object in Step Functions .

   3. In the box that appears, enter the following as message:

      {
        "TaskToken.$": "$$.Task.Token"
      }

   4. Choose the Wait for callback checkbox.

   5. Choose Done in the dialog box that appears.

4. Keep this window open and proceed to the next topic.