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SimpleWorkflowFramework.NET

SimpleWorkflowFramework.NET is a helper library to simplify writing code for Amazon Web Services (AWS) Simple Workflow Framework (SWF) in C#. Currently, AWS hasn't released a Flow framework for the C# language, so developers have to write their own event handling logic if they wish to use SWF from C#.

As part of trying to understand the semantics of SWF, I ended up writing a library that generalizes the common code and greatly simplifies writing simple workflows. SimpleWorkflowFramework.NET is the result.

As of today, the events we callback on are:

  • WorkflowExecutionStarted
  • WorkflowExecutionContinuedAsNew
  • WorkflowExecutionCancelRequested
  • ActivityTaskCompleted
  • ActivityTaskFailed
  • ActivityTaskTimedOut
  • ScheduleActivityTaskFailed
  • ChildWorkflowExecutionStarted
  • ChildWorkflowExecutionCompleted
  • ChildWorkflowExecutionFailed
  • ChildWorkflowExecutionTerminated
  • ChildWorkflowExecutionTimedOut
  • StartChildWorkflowExecutionFailed
  • TimerStarted
  • TimerFired
  • TimerCanceled

Features not yet implemented:

  • Signals

To implement a workflow to receive event callbacks, you will need to implement the IWorkflowDecisionMaker interface or inherit WorkflowBase which contains a default implementation for handling the common case workflows.

Below I outline a simple use case based on the canonical Amazon workflow example:

[Customer Order Workflow]                                                                                     
               +--------------+                                                 +------------+          		 
(start)   =>   | Verify Order |   =>   < Verify Customer Child Workflow>   =>   | Ship Order |   => (end)	 
               +--------------+                                                 +------------+				 
			                                         ^															 
												   /   \														 
      .-------------------------------------------       -----------------------------------------------.	 
     /                                                                                                   \	 
               +-------------------------+        +----------------+        +--------------------+          	 
(start)   =>   | Verify Customer Address |   =>   | Check Fraud DB |   =>   | Charge Credit Card |   => (end) 
               +-------------------------+        +----------------+        +--------------------+			 
[Verify Customer Workflow]

In order to run the code you will need an AWS account and the following workflows and activities need to be registered:

Workflows

  • CustomerOrderWorkflow
  • VerifyCustomerWorkflow
Common properties for the workflows
  • Version: 1.0
  • TaskList: DeciderTaskList-Default
  • Default Timeouts: 60 seconds
  • Child Policy: Terminate

Activities

  • ChargeCreditCard
  • CheckFraudDB
  • ShipOrder
  • VerifyCustomerAddress
  • VerifyOrder
Common properties for the workflows
  • Version: 1.0
  • TaskList: ActivityTaskList-Default
  • Default Timeouts: 60 seconds

Once the activities and workflows are registered, we need to define a dictionary in our code to let event processor know which workflows we want it handle and call back on:

// Define the workflows that we know of that event processor will be handling
var workflows = new Dictionary<string, Type>
    {
        {"CustomerOrderWorkflow", typeof (CustomerOrderWorkflow)},
        {"VerifyCustomerWorkflow", typeof (VerifyCustomerWorkflow)}
    };

Then wait for a decision and call the events processor to handle the event:

var workflowProcessor = new WorkflowEventsProcessor(decisionTask, workflows);
var decisionRequest = workflowProcessor.Decide();

And here's the definition for a workflow:

public class CustomerOrderWorkflow : WorkflowBase
{
    public CustomerOrderWorkflow()
    {
        WorkflowSteps = new ISetupContext[]
        {
            // An activity
            new WorkflowActivitySetupContext
                {
                    ActivityName = "VerifyOrder",
                    ActivityVersion = "1.0",
                    ActivityId = Guid.NewGuid().ToString(),
                    Control = "",
                    Input = "",
                    ScheduleToCloseTimeout = "60",
                    TaskList = "ActivityTaskList-Default",
                    ScheduleToStartTimeout = "60",
                    StartToCloseTimeout = "60",
                    HeartbeatTimeout = "NONE"
                },

            // Followed by a child workflow
            new WorkflowSetupContext
                {
                    TagList = new List<string>(),
                    WorkflowName = "VerifyCustomerWorkflow",
                    WorkflowVersion = "1.0",
                    WorkflowId = Guid.NewGuid().ToString(),
                    Control = "",
                    Input = "",
                    ExecutionStartToCloseTimeout = "600",
                    TaskList = "DeciderTaskList-Default",
                    TaskStartToCloseTimeout = "60",
                    ChildPolicy = "TERMINATE",
                },

            // Followed by another activity
            new WorkflowActivitySetupContext
                {
                    ActivityName = "ShipOrder",
                    ActivityVersion = "1.0",
                    ActivityId = Guid.NewGuid().ToString(),
                    Control = "",
                    Input = "",
                    ScheduleToCloseTimeout = "60",
                    TaskList = "ActivityTaskList-Default",
                    ScheduleToStartTimeout = "60",
                    StartToCloseTimeout = "60",
                    HeartbeatTimeout = "NONE"
                }
        };
    }
}

For detailed information, please refer to the code as that is really the best guide.

NuGet Package Information

A NuGet package is also available for this library. More information at https://nuget.org/packages/SimpleWorkflowFramework.NET/

Contributors:

  • Shawn Debnath
  • Michael Teper
  • Matt Strom

There's a lot that can be done to improve this library and make other's lives easier and this project could definitely use some help. I encourage folks to clone the repository, make improvements, be it code, features, documentation, tests ... anything. You can either send me a pull request or a diff/patch and I can add you as a collaborator. I will also be glad to add your name to the list of contributors.

If you would like to discuss a topic, feel free to email me at the link on https://github.com/sdebnath.