Is there any way to know if a Lambda was invoked by a step function?

Question

Is there any way for a lambda function to know if it was invoked inside a step function? Without requiring the developer to pass arguments inside the step function from step to step. I checked the context and it does not provide such information.

I would imagine that aws would provide some kind of unique identifier for step functions which would be passed to lambda functions.

Answer 1

There is no default way to do so. Step Functions by itself does not pass any event details when invoking a Lambda function.

As you mentioned, you can pass input via the InputPath, ResultPath and OutputPath from step to step. Alternatively, you can declare Parameters in your state machine:

{
     "StartAt": "HelloWorld",
     "States": {
         "Echo": {
             "Type": "Task",
             "Resource": "arn:aws:lambda:us-east-1:1234567890:function:echo",
             "Parameters": {"invocation_type": "StepFunction"},
             "End": true
          }
     }
}

The above function will be invoked with {"invocation_type": "StepFunction"} event.