What kind of Host Application to use?

What kind of Host Application to use?

• Joe Au

  The expense reporting application shows a good example of using WCF to host your workflow runtime seperate from the client application.

  There is a ton of information about WCF on the web. Check out MSDN and www.windowscommunication.net for examples and articles.

  I think it is a bad idea to host the workflow service in a windows forms or console application on a server. Workflow works really well in those hosts if they are on a client and being interacted with. Neither of these works well on an unattended server. You want a windows service for that. with .NET these services are not any harder to write than a console application, just a bit harder to debug sometimes. In the case of workflow, it shouldn't be an issue.

  Matt

  
  
  

• DotNetDevelop

  One set of interfaces is for the WCF service contract, while one is for the local WF services. there is then an implementation of each. The local services provide the connectivity to the workflow, while the WCF services perform the routing logic and call the local services to raise events to the workflow.

  the IndigoUtil project has a WCF extension that gets executed at startup and shutdown of the WCF service host. This makes sure the WF runtime is running and available. Then the WCF service code can access the instance of the runtime through this extension.

  Matt

  
  
  

• GregWold

  I try to understand the ExpenseReporting example (please correct me if I'm wrong):

  There are 8 projects in the solution:

  • ExpenseActivities: The Custom Activities library
  • ExpenseApplication: Windows Forms app, communicating with the Host
  • ExpenseContracts: The Business Logic layer
  • ExpenseHost: The Host for the Workflow Runtime
  • ExpenseLocalServices
  • ExpenseWorkflows: The Workflow itself
  • IndigoUtil
  • ManagerApplication: Windows Forms app, communicating with the Host

  Could someone explain the communication in this example. There are 2 interfaces, one in the ExpenseContracts project called "IExpenseService.cs", and the other one in the ExpenseLocalServices project called "IExpenseLocalService.cs".

  Why are there 2 interfaces Where is the difference between them Is there any particular reason why "IExpenseService.cs" is in the ExpenseContracts project What is the IndigoUtil project used for

  I could use some help on that please.

  -------------------------------------------

  I thought about my application, and think that I will implement a Windows Service as a host for the workflow runtime environment. This service will be able to communicate with a website, using some communication method (which I dont know by now).

  There are also projects for the custom activities library and the workflows itself.

  I'll start off trying to implement this service and get the runtime running. Afterwards I start building activities and workflows. Hope I works...

  Thanks

  
  

• Pratish

  Following on to Matt's post above, you can check out the expense reporting application which hosts the workflow inside a WCF service. It's currently set up as a console app, but you could convert it to a Windows service pretty easily. You wouldn't host the workflow inside your ASP.NET application, but you would use the ASP.NET ordering application to start the workflow by calling into the service. In the sample, a Windows application calls the service, but you can do the same thing from a web application.
  
  You can get that sample here:
  
  http://www.windowsworkflow.net/default.aspx tabindex=4&tabid=49
  
  
  

• Mabbus

  So you say, that I need to bring my web application up again, in order to continue the workflow. This is a problem...

  I need following:

  • There is a asp.net website where orders are made.
  • After the order is submitted, the workflow starts.
  • The first thing to do, is clearance of the order by human intervention, using the asp.net website.
  • Then there are several escalations to check for the order. e.g. if a order does not reach a previously defined state in a user defined amount of time, emails are sent to the according persons, and the workflow goes on.
  • Then after the order has been completely configurated, and reached the internal closed status the workflow end.

  This means that the Workflow has to run, even if the webapplication is down. Do you have any suggestions, how to host the runtime for such a scenario

  Are there more examples for hosting the runtime engine in an asp.net application And are these capable of more than just printing out "Hello World"

  Thanks

  
  

• prjuanl

  If you use ASP.Net, you need to use the persistence service to make sure your workflow instance doesn't get lost with a process recycle. You also have to take into consideration that while the workflow instance will be reloaded when the timer is up, you need to write some code to actually execute it using the RunWorkflow method of the manualworkflowscheduler. You might try registering for the workflowloaded event on the runtime on application start and then put some logic in the event handler to run the workflow if a delay has elapsed.

  Matt

  
  
  

• doubletree

  Host the runtime in the windows service, and not in the ASP.NET application. Use remoting or services to communicate between the two. See the other post on this thread for a link to an example of using WCF to communicate between a client application and "remote" host for the workflow runtime.

  Matt

  
  
  

• Michael Goffioul

  The point in using the persistence service is evident to me. This way I can save the actual workflow to the database, and reload it. What kind of instance does the evaluation of the timer, when the asp.net website is down

  In your post you say, that I need to write some code for executing it, after a reload from the database. Which I could do by registring for the workflowLoaded event on the runtime application start. Did I get that right

  I thought about following: What about a Windows Forms Application which runs on the server, where the web app is hosted. If someone on the web app makes a order, the windows forms app starts a workflow for this particular order, and manages it. In case of shutdown it needs to reload the workflows using the persistence service. Also I would have an app in which you can see the status of all running workflows (when they were started, how long they are idle, ....) What do you think

   

  
  

• ATAMAN

  Does anyone has good examples/tutorials on creating such a service. I am new to this topic, and therefore would appreciate having a bit of a guidline.

  But to make that clear, you guys would suggest following:

  • Host Application: Windows Communication Foundation Service hosting the WorkflowRuntime; starting and managing the workflows, as well as persistence and so on
  • Client Application: Asp.net Ordering Web Application
  • Communication between them: WCF

  Are there also some good informations about the communication between the host and the client

  Is it a bad idea to host the workflow runtime engine in a console or windows forms application, for using it in my app (as described above)

  Thanks

  
  

• KrazyKiwi

  Matt,
  
  Using this architecture, is it true to say that the relationship then becomes client to host to runtime Which means that communications between workflow and client apps becomes somewhat problematic. Can you use ExternalDataExchange in this case ExternalDataExchange usually communicates with the host, doesn't it
  
  
  

• Greg3055

  Thanks guys for your quick and helpful reply. I try to get my basic application setup working today. Hopefully.

  I'll write some if I got problems or if I get it working.

  
  

• Bursteg

  Communication with the host becomes different, but not necessarily problematic. You can wrap local communications (externaldataexchange) with WCF or remoting. The differences include:

  1) Having to manage/map from WCF requests to workflow events. Not usually to hard as you can have your request type be part of the event arguments and simply wrap it up and pass it in. You have to manage the workflow instance ID which you have a number of options for doing, including putting it right in the request message as is done on the expense reporting application.

  2) Having to communicate from the server to the client. This area provides for a few options. You can update some common data store (in memory or persistent) and have the client poll that (or use sql dependencies in sql 2005). You can also use duplex contracts in WCF to call back to the client, or have the client host a service as well that you call from the runtime host.

  There are other options depending on your workflow and architecture choices. In the future there will be WCF activities that might make some of this easier, but we'll have to wait a while for those.

  Matt

  
  
  

• Paul Dettorre

  Hi Matt

  Thanks for explaining. But I still have some trouble understanding.

  The IndigoUtil is a WCF extension. It allows me to access the instance of the runtime. Also it starts and stops the runtime on start or stop. I think I understood that.

  But the 2 interfaces are still somewhat unclear to me. I try to develop an application using such interfaces, but I dont really know where to start, or what to implement. It confuses me. Maybe you could give me a little step by step explanation on what I have to do to communicate between:

  • WorkflowHost: Windows Service
  • Workflow
  • WorkflowClient: ASP.NET Application

  I need these 3 to communicate with each other. But I just dont know where to start, or what to use for.

  Thank you

  
  

• roy_wang

  The persistence service itself is checking the database for timers. So if you host in ASP.NET and your application is not running, nothing is checking until the app comes back up.

  You are right, you can register for the workflow loaded event which will let you know when a workflow has been loaded from the persistence store.

  I would not create a windows forms app on the server, but you could create a windows service that exposes an interface via remoting or web services. You could have one service interface to interact and start the workflow or raise events to it and another interface that allows a remote or local winform app to query for all the details you would like to have. The service gives you the benefits of being able to have your workflow runtime loaded at startup and have control over starting and stopping it from the services admin tool. It also allows you to run as a particular identity.

  The real issue is that when you run workflows in ASP.NET, you typically use the ManualWorkflowScheduler service because you want to use the app thread for running workflows. With a Windows service, you generally use the DefaultWorkflowSchedulerService which runs things asynchronously. You'll need to keep this in mind as you develop your local services, the service interface for your workflow host, and the application itself.

  Matt

  
  
  
• What kind of Host Application to use?