Maestro BPMN
Synopsis
Lightweight BPMN Interpreter in C#.Net
Goal
An architecture with a workflow engine means either all called services return to the engine to continue the current process (SOA) or services have knowledge of other services (microservice architecture) meaning you have interactions which are managed outside of the scope of the engine.
Primary goal is to have both business processes and service to service interactions defined with BPMN in a single place and executed by the relevant service.
Usual BPMN engines are heavy and offer BPMN features which are not needed by all services. They are not suitable to be deployed along with a lightweight service. This project aims to provide a lightweight dependancy making a service BPMN ready. This service only does what it is supposed to do leaving the interaction with other services to be decided by business processes.
Another issue with usual BPMN engines is dealing with process variables. Usual engines use process variables as a holder of inputs and outputs. Nodes map their variables from the process variables and map their outputs back to the process variables, introducing racing and state issues when multiple branches are sharing the same process variables.
[Current work in progress]
To avoid side effects, a node should take its inputs from a local context initialy built from the process variables, and return outputs which are used as local context for the next node. If the variable is not found in the local context, it will be resolved from the process variable inputs. For multibranch workflows, diverging gateways should clone the previous node outputs for each branch and converging gateways should merge or aggregate the sets of outputs.
Features
-
Start a BPMN workflow with custom handlers for any element.
-
Dispatch a BPMN workflow to be executed by another service.
-
A default implementation of InclusiveGateway element handling, waiting for all branch to reach before continuing. Known defect: if a branch has a conditional sequence, it is possible that it will never reach the gateway and the gateway will wait forever. Possible fix: premature endEvent from a conditional sequence could create a tree of unreachable branches connecting to an InclusiveGateway.
-
A default implementation of ScriptTask element handling running C# code via Roslyn Scripting
-
A default implementation of conditional sequence element handling evaluating a C# condition via Roslyn Scripting.
TODO
-
Dynamic load of BPMN to be sent (currently remote BPMN process is passed as a process variable)
-
Default Business rules handler (possibly with DMN support)
-
InclusiveGateway process variables merge/aggregate
-
Process/Parameters serialization
-
Swimlane support (send the swimlane to a target service to execute)
Examples
Demo BPMN workflow
Example 1: Running as local workflow
Result
Local workflow execution
using Maestro;
namespace WorkflowConsoleApp
{
class Program
{
static void Main(string[] args)
{
var p = new Process("flow.bpmn");
var processInstance = p.NewProcessInstance();
processInstance.SetDefaultHandlers();
processInstance.SetHandler("task", new MyTaskHandler());
processInstance.SetHandler("startEvent", new MyStartHandler());
var processVar = new Dictionary<string, object>() { { "processVar1", "value" }, { "processVar2", 50 } };
processInstance.Start(processVar);
Console.ReadLine();
}
private class MyStartHandler : INodeHandler
{
public void Execute(ProcessNode currentNode, ProcessNode previousNode)
{
Console.WriteLine("Custom Start Handler");
Console.WriteLine(currentNode.NodeName);
currentNode.Done();
}
}
private class MyTaskHandler : INodeHandler
{
public void Execute(ProcessNode currentNode, ProcessNode previousNode)
{
Console.WriteLine("Custom Task Handler");
Console.WriteLine(currentNode.NodeName);
currentNode.Done();
}
}
}
}
Example 2: Running as SOA/microservice workflow with remote BPMN execution
Using the demo BPMN flow. Custom Task handler is set to send this flow to be executed remotely
This flow contains a task to execute on a third service
Result
Initial workflow service
using Maestro;
namespace ZMQExample
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Main Workflow Component");
var p = new Process(File.OpenRead("flow.bpmn"));
var processInstance = p.NewProcessInstance();
processInstance.SetDefaultHandlers();
processInstance.SetHandler("task", new ZMQTaskHandler());
var processVar = new Dictionary<string, object>() { { "processVar1", "value" }, { "processVar2", 50 }, { "Task2BPMN", File.ReadAllText("microflow.bpmn") } };
processInstance.Start(processVar);
Console.ReadLine();
}
private class ZMQTaskHandler : INodeHandler
{
public void Execute(ProcessNode currentNode, ProcessNode previousNode)
{
string endpoint = "tcp://127.0.0.1:5555";
// Create
using (var context = new ZContext())
using (var requester = new ZSocket(context, ZSocketType.REQ))
{
// Connect
requester.Connect(endpoint);
string requestText;
//testing for NodeName because retrieving node variables is not yet implemented.
if (currentNode.InputParameters.ContainsKey("Task2BPMN") && currentNode.NodeName == "Task_2")
{
requestText = (string)currentNode.InputParameters["Task2BPMN"];
Console.WriteLine("Request {0}", "Remote BPMN start");
}
else
{
requestText = "Do some work";
Console.WriteLine("Request {0}", requestText);
}
requester.Send(new ZFrame(requestText));
using (ZFrame reply = requester.ReceiveFrame())
{
Console.WriteLine("Received: {0} ", reply.ReadString());
}
currentNode.Done();
}
}
}
}
}Remote Service receiving a workflow to execute
using Maestro;
namespace ZMQExampleService
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("BPMN worker server");
// Create
using (var context = new ZContext())
using (var responder = new ZSocket(context, ZSocketType.REP))
{
// Bind
responder.Bind("tcp://*:5555");
while (true)
{
// Receive
using (ZFrame request = responder.ReceiveFrame())
{
var flow = request.ReadString();
if (flow.StartsWith("<?xml")) //Just for demo purposes
{
var p = new Process(new MemoryStream(Encoding.UTF8.GetBytes(flow)));
var processInstance = p.NewProcessInstance();
processInstance.SetDefaultHandlers();
processInstance.SetHandler("task", new ZMQTaskHandler());
processInstance.Start(new Dictionary<string, object>());
}
responder.Send(new ZFrame("Work Done"));
}
}
}
}
private class ZMQTaskHandler : INodeHandler
{
public void Execute(ProcessNode currentNode, ProcessNode previousNode)
{
string endpoint = "tcp://127.0.0.1:5556";
using (var context = new ZContext())
using (var requester = new ZSocket(context, ZSocketType.REQ))
{
// Connect
requester.Connect(endpoint);
string requestText = "Do some work";
Console.WriteLine("Request {0}", requestText);
requester.Send(new ZFrame(requestText));
using (ZFrame reply = requester.ReceiveFrame())
{
Console.WriteLine("Received: {0} ", reply.ReadString());
}
currentNode.Done();
}
}
}
}
}Remote Service called by the previous service workflow
namespace ZMQExampleServiceWithoutMaestro
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("10 seconds worker server");
using (var context = new ZContext())
using (var responder = new ZSocket(context, ZSocketType.REP))
{
responder.Bind("tcp://*:5556");
while (true)
{
// Receive
using (ZFrame request = responder.ReceiveFrame())
{
Console.WriteLine("Received {0}", request.ReadString());
// Do some work
Thread.Sleep(10000);
Console.WriteLine("Sending Work Done");
responder.Send(new ZFrame("Work Done"));
}
}
}
}
}
}