This project shows how to use the Map state for AWS Step Functions to process data in parallel workflows. The project uses AWS CDK for deploying the infrastructure. Please edit the config.json file to configure the resources as required.

This project creates an AWS Step Functions state machine that will read a list of items from a DynamoDB table, and then pass it to the Map state of the statemachine. The Map state processes the items from the list in parallel. For this project for every item, a virtually empty Lambda Function is invoked. The function simply logs the value passed to it.

The resources deployed in this project are in the file lib/stpfnc-stack.ts. The stack creates a DynamoDB table, a Lambda function, and a State Machine. The state machine reads from the DynamoDB table, gets a list of items, and invokes the Lambda function for each of the items.

The utils folder has the load-ddb.py file to load the created DynamoDB table with sample list of items. The folder has two sample JSON files with list of items that you can use to load the table, and test the state machine's map state.

This is the state machine created by this project.

1. An AWS Account
2. AWS CDK installed and setup. Please note AWS CDK is constantly improved with new versions released frequently. This project is deployed and tested with AWS CDK Version 2.92.0.

Please note that this stack is likely to incur cost (it is not free!). Remeber to destroy the stack as shown below. You should be familiar with use cdk commands and ensure that the region you are using is cdk bootstrapped.

To install, clone the respository and deploy using default AWS credentials:

cdk deploy 

If you prefer to specify your AWS profile for the account/region:

cdk deploy --profile <your profile name here>

A successful deployment will result in the State Machine ARN and Name being printed to the console (it will have the AWS Account Number and Region specific to your deployment:

Outputs:
StpfncStack.StateMachineArn = arn:aws:states:us-east-1:xx22yy12zz76:stateMachine:TestStateMachine3C216BE3-cNqHpgOztjDN
StpfncStack.StateMachineName = TestStateMachine3C216BE3-cNqHpgOztjDN
Stack ARN:
arn:aws:cloudformation:us-east-1:xx22yy12zz7:stack/StpfncStack/47730ab0-8353-11ee-995c-0aa42affc2ab

1. Once the stack is created, before starting the State Machine execution, you will need to load the list of items in the DynamoDB table. The project provides sample data and Python script to load in the DynamoDB table. There two sample lists: simplelist.json and listofdicts.json. The first is simple list of three subjects - Computer Science, Economics, and Mathematics. The second list is a list of dictionaries, each dictionary has the topic and name keys.

cd utils
python load-ddb.py --config ../config.json --profile <your-aws-profile> --json simplelist.json

The command above loads the simple list into the DynamoDB table. When you explore items in the DDB table, here is what the loaded simple list looks like:

2. You can start the execution of the state machine from the Step Functions console or the command line. Here is how to start an execution from the command line (using the State Machine ARN from the output of the cdk deploy):

aws stepfunctions start-execution --state-machine-arn arn:aws:states:us-east-1:xx22yy12zz76:stateMachine:TestStateMachine3C216BE3-cNqHpgOztjDN --input {} --profile <your-aws-profile>

The command above will return (NOT wait for execution to finish) with an executionArn. 3. You can either use the executionArn to use the describe-execution to get the status of the State Machine execution. Or you can use the console. Here is what you would see on successful execution:

Here is a screenshot from the console of a successful run - it shows the Graph view plus details on the LambdaInvoke section - since it was selected prior to taking the screenshot:

4. On the right hand side you can see the Input to the LambdaInvoke step, and if you go click on the Log group - you can see the output of the event passed to the Lambda function:

You can see that the Lambda function was invoked three separate times - once for each of the 3 items in the list. Take a look at the timestamps of each invocation - what do you notice? They are about 2 seconds apart. This is because the State Machine as a Wait State of 2 seconds, and a Concurrency of 1 (see default values in config.json). The invocations are 2 seconds apart because given single concurrency the State Machine invokes Lambda one at a time, and the Map state has 2 second wait. The state machine goes through the Map state and then invokes the Lambda second and third time 2 seconds apart.

1. Set the maxConcurrency in the config.json to 3 or higher. Deploy the stack again to change the configuration of the State Machine. Execute and observe results. With the concurrency 3 or higher - the Lambda function will be invoked 3 times almost at the same time in parallel (you can see it in the timestamps of the log or the timing in the Events console below Graph view).

2. Try loading the DDB table with the listofdicts.json. Run the state machine. And observe the items that get passed to the Lambda function. You will observe a DynanmoDB M passed with the individual key-value pairs passed along.

3. Increase the waitDurationSeconds to 25 seconds, with the timeoutDurationSeconds to be at 20. Deploy the stack again to update the configuration. Now when you run the state machine - it should fail due to a timeout.

After you are done, to destroy the stack:

cdk destroy

• Dynamo DB table has a removal policy of DESTROY applied since this is for learning/testing. If you intend to use this code for production please change the removal policy for resources as needed.