Workflows

This package implements a workflow interpreter based on the Amazon States Language specification.

Installation

This package can be installed by adding workflows to your list of dependencies in mix.exs:

def deps do
  [
    {:workflows, "~> 0.1.0"}
  ]
end

Usage

Workflows implements an Amazon States Language interpreter using event-sourcing, this has the added benefit that workflows can be suspended and later recovered.

Workflows are created by parsing a map with the workflow definition that conforms to the Amazon States Language specification.

workflow_definition = %{
  "StartAt" => "Start",
  "States" => %{
    "Start" => %{
      "Type" => "Wait",
      "Seconds" => 10,
      "Next" => "End"
    },
    "End" => %{
      "Type" => "Succeed"
    }
  }
}
{:ok, workflow} = Workflows.parse(workflow_definition)

You can then start the workflow by calling the Workflows.start function and passing a context (a map containing data that is shared between all states), and the arguments passed to the initial state. The function returns {:continue, execution, events} if the workflow execution has to stop to wait for an external command, or {:succeed, result, events} if the workflow executes to termination.

ctx = %{"environment" => "staging"}
args = %{"user" => "alfred@example.org"}
{:continue, execution, events} = Workflows.start(workflow, ctx, args)
IO.inspect events

The interpreter does not execute side effects like waiting for a timer or executing a task, instead it returns an event (for example, Event.WaitStarted or Event.TaskStarted) and pauses the execution. To resume execution, you should call the Workflows.resume function with a Command containing the side effect result (for example, the result of a Task).

wait_event = events |> get_wait_event()
finish_wait = Workflows.Command.finish_waiting(wait_event)
{:succeed, result, events} = Workflows.resume(execution, finish_wait)

You can restore a workflow execution state from its events with the Workflows.recover function.

{:continue, execution, new_events} = Workflows.recover(workflow, events)

License

This repo is licensed under Apache 2.0.