I’m developing an intranet site using asp.net mvc4 to manage some of our data. One important feature of this site is to trigger import/export jobs. These jobs can take anywhere between 5 minutes to 1 hour. Users of the site need to be able to determine whether a job is currently running as well as the status of prior jobs. Many jobs will often include warning messages concerning duplicate data and these warnings need to be visible on the site.
My plan is to implement these long running processes as a WCF Workflow Service that the asp.net site will interact with. I’ve got much of the business logic implemented via activities and have tested it using a simple console application. I should note I’m using a correlation handle in order to partition the service based on specific “Projects” on the site.
My problem is how do I go by querying the status of an active job (if one exists) as well as the warning messages of previous jobs. I suspect the best way to do this would be to use the AppFabric tracking service and have my asp.net query a SQL monitoring store and report back on the current status. After setting up AppFabric and adding custom tracking messages, I ran into a few issues. My first issue is that I cannot figure out how to filter out workflow instances that were not using the correct correlation handle as I’d like to show only workflows for a specific project. The other issue is that the tracking database can be delayed quite a bit which causes issues for me trying to determine if a workflow is currently running.
Another possible solution could be to have the workflow explicitly update a database with its current status and any error messages. I’m leaning towards this solution but could use some expert advice.
TL;DR: I need to know the best way to query the execution status and any warning messages of a WCF Workflow service.
As you want to query workflow status and messages even after the workflow is finished I would start by creating a table where you can convert the correlation values a client send to the related workflow ID. I would create a custom activity to do that and drop it right after the receive that creates the workflow.
Next I would create a regular WCF service the client app uses to query the status. This WCF service can query the WF persistence store to see if a given workflow is still running. If so the active bookmarks column will tell you what SOAP messages the workflow is currently waiting for.
As far as messages go you can either use the AppFabric tracking infrastructure to store and retrieve them or you could create a custom activity and store them in your own database. It really depends if you are also interested in the standard WF tracking messages generated.
Update on cheking for running workflow instances:
There are several downsides to adding an IsRunning message to your workflow. For one you would need to make sure one branch keeps looping and waiting for the message but stops as soon as the other real workflow branch is done. Certainly possible but it complicates the workflow and is a possible source of errors. And as it is not part of the business problem it really has no place in the workflow as far as I am concerned. It also means that you will have to load a workflow from disk and persist it back just to tell you that it is there. If it was finished you will need to wait for a fault to indicate there was no workflow instance. And that usually means you get a timeout exception after, by default, 60 seconds. Add throttling to that and you request might be queued because there are too many other workflow instances or SOAP request being processed. So a timeout might mean that a workflow instance exists but is unreachable due to system constraints. Instead I would opt for the simple thing and check if the record in the instance store is still available. The additional info from the active bookmarks column will tell you what the workflow is waiting on, information I have used in the past to dynamically update the UI by enabling/disabling UI elements.