AWS StepFunctionsLocal StepFunctions test with definition substitutions

Question

I have been looking into StepFunctionsLocal (SFL) to test. To get a project bootstrapped, I aws the SAM cli to generate a new project - which comes pre-packed with SFL tests and a make file to run everything.

However, it seems broken out of the box. When running the tests using directions in the README, I get this error:

InvalidDefinition: An error occurred (InvalidDefinition) when calling the CreateStateMachine operation: Invalid State Machine Definition: ''SCHEMA_VALIDATION_FAILED: Value is not a valid resource ARN at /States/Check Stock Value/Resource','SCHEMA_VALIDATION_FAILED: Value is not a valid resource ARN at /States/Sell Stock/Resource', 'SCHEMA_VALIDATION_FAILED: Value is not a valid resource ARN at /States/Buy Stock/Resource', 'SCHEMA_VALIDATION_FAILED: Value is not a valid resource ARN at /States/Record Transaction/Resource''

And, indeed, the state machine definition is provided as a file that uses DefinitionSubstitutions:

{
    "Comment": "A state machine that does mock stock trading.",
    "StartAt": "Check Stock Value",
    "States": {
        "Check Stock Value": {
            "Type": "Task",
            "Resource": "${StockCheckerFunctionArn}", <--
            "Retry": [
                {
                    "ErrorEquals": [
                        "States.TaskFailed"
                    ],
                    "IntervalSeconds": 15,
                    "MaxAttempts": 5,
                    "BackoffRate": 1.5
                }
            ],
            "Next": "Buy or Sell?"
        },
...

The CloudFormation template injects those values

StockTradingStateMachine:
    Type: AWS::Serverless::StateMachine # More info about State Machine Resource: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-resource-statemachine.html
    Properties:
      DefinitionUri: statemachine/stock_trader.asl.json
      DefinitionSubstitutions:
        StockCheckerFunctionArn: !GetAtt StockCheckerFunction.Arn <--

the makefile commands to run the test

run:
    docker run -p 8083:8083 -d \
    --mount type=bind,readonly,source=$(ROOT_DIR)/statemachine/test/MockConfigFile.json,destination=/home/StepFunctionsLocal/MockConfigFile.json \
    -e SFN_MOCK_CONFIG="/home/StepFunctionsLocal/MockConfigFile.json" \
    amazon/aws-stepfunctions-local

create:
    aws stepfunctions create-state-machine \
        --endpoint-url http://localhost:8083 \
        --definition file://statemachine/stock_trader.asl.json \
        --name "StockTradingLocalTesting" \
        --role-arn "arn:aws:iam::123456789012:role/DummyRole" \
        --no-cli-pager \
        --debug

happypathsellstocktest:
    aws stepfunctions start-execution \
        --endpoint http://localhost:8083 \
        --name HappyPathSellStockTest \
        --state-machine arn:aws:states:us-east-1:123456789012:stateMachine:StockTradingLocalTesting#HappyPathSellStockTest \
        --no-cli-pager

It appears that nothing provides the definition substitutions. I've come up dry when combing through the AWS docs for how to provide those substitutions through the API, maybe I just don't know what to look for. Any clues?

I did make an issue to fix the template: https://github.com/aws/aws-sam-cli-app-templates/issues/342

Answer 1

Unfortunately, DefinitionSubstitutions is a feature of the CloudFormation resource and not supported directly in the Step Functions API. You would need to parse and replace the substitution variables in your own code before you call Create State Machine in your test.