Can AWS Step Function describe this kind of dataflow?

Question

dataflow

It can not be described with Parallel State in AWS Step Function.

B and C should be in parallel.

C sends messages to both D and E.

D and E should be in parallel.

which ones need to run in parallel? – Horatiu Jeflea Sep 26 '19 at 18:46 — Horatiu Jeflea, Sep 26 '19 at 18:46
@HoratiuJeflea B in parallel with C, D in parallel with E – Tauta Sep 26 '19 at 20:36 — Tauta, Sep 26 '19 at 20:36
@LostJon I want to invokes both successors. – Tauta Sep 26 '19 at 20:37 — Tauta, Sep 26 '19 at 20:37

score 2 · Answer 1 · answered Sep 27 '19 at 09:46

{
    "StartAt": "A",
    "States": {
        "A": {
            "Type": "Pass",
            "Next": "Parallel State 1"
        },
        "Parallel State 1": {
            "Type": "Parallel",
            "Branches": [{
                    "StartAt": "B",
                    "States": {
                        "B": {
                            "Type": "Pass",
                            "End": true
                        }
                    }
                },
                {
                    "StartAt": "C",
                    "States": {
                        "C": {
                            "Type": "Pass",
                            "End": true
                        }
                    }
                }
            ],
            "Next": "Parallel State 2"
        },
        "Parallel State 2": {
            "Type": "Parallel",
            "Branches": [{
                    "StartAt": "D",
                    "States": {
                        "D": {
                            "Type": "Pass",
                            "End": true
                        }
                    }
                },
                {
                    "StartAt": "E",
                    "States": {
                        "E": {
                            "Type": "Pass",
                            "End": true
                        }
                    }
                }
            ],
            "Next": "F"
        },
        "F": {
            "Type": "Pass",
            "End": true
        }
    }
}

vaquar khan · Answer 2 · 2019-09-27T13:08:07.270

Answer is No , inside step function no state can set multiple states (invokes both successors)to its Next task. As per AWS step function cannot start State Machine as StartAt by providing multiple State names.

You can tweak your logic and use The Parallel state and achive same ,If you share your usecase may be help to solve problems.

How to specify multiple result path values in AWS Step Functions

A Parallel state provides each branch with a copy of its own input data (subject to modification by the InputPath field). It generates output that is an array with one element for each branch, containing the output from that branch.

https://aws.amazon.com/blogs/aws/new-step-functions-support-for-dynamic-parallelism/

Example of state function

{
  "Comment": "An example of the Amazon States Language using a choice state.",
  "StartAt": "FirstState",
  "States": {
    "FirstState": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:REGION:ACCOUNT_ID:function:FUNCTION_NAME",
      "Next": "ChoiceState"
    },
    "ChoiceState": {
      "Type" : "Choice",
      "Choices": [
        {
          "Variable": "$.foo",
          "NumericEquals": 1,
          "Next": "FirstMatchState"
        },
        {
          "Variable": "$.foo",
          "NumericEquals": 2,
          "Next": "SecondMatchState"
        }
      ],
      "Default": "DefaultState"
    },

    "FirstMatchState": {
      "Type" : "Task",
      "Resource": "arn:aws:lambda:REGION:ACCOUNT_ID:function:OnFirstMatch",
      "Next": "NextState"
    },

    "SecondMatchState": {
      "Type" : "Task",
      "Resource": "arn:aws:lambda:REGION:ACCOUNT_ID:function:OnSecondMatch",
      "Next": "NextState"
    },

    "DefaultState": {
      "Type": "Fail",
      "Error": "DefaultStateError",
      "Cause": "No Matches!"
    },

    "NextState": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:REGION:ACCOUNT_ID:function:FUNCTION_NAME",
      "End": true
    }
  }
}

score 0 · Answer 3 · answered Sep 27 '19 at 18:58

As I answered in How to simplify complex parallel branch interdependencies for Step Functions, what you asked is better to be modeled as DAG but not state machine.

Depends on your use case, you might be able to workaround it (just as @horatiu-jeflea 's answer), but it's a workaround (not the straightforward way) anyway.

Can AWS Step Function describe this kind of dataflow?

3 Answers3