Thank you. I feel kind of silly about this but I feel like I've had a hard time understanding when an org should, or could use something like this. I have seen them mentioned but every time it's explained it's explained with more abstract language on top of it that confuses me. I keep hearing "it manages business processes" but then it fails to mention if this means like, a human being's process within an org, or something coupled with an application of some sort that has business processes in the application? Does this type of thing replace sort of what Jira does, make a ticket and then pass it off to the next team or whatever? Do you ship it with the app for on-premise deployments of a software product? I have a hard time seeing the big picture with things like this sometimes. Then I hear workflow orchestrator and I think, oh okay so like ansible, but for, work...flows? But what is a workflow really exactly?
This could also be used to kill off systems like SharePoint in many businesses and that would be great.
Seriously, its workflow engine has race conditions, randomly fails and has no transaction management. But there are few alternatives. I don't know why there hasn't been any real contender. You would need a full suite to challange it though.
Yep! The one thing I would change though is that it's common for workflows to be started by an event. So in your example, the first step would be UserService.signupUser, that emits a sign-up event, that starts a workflow that sends the email.
Without the workflow/orchestration, we're effectively coupling the EmailService to the UserService, and it's that type of coupling that reduces reusability and isolation.
Thank you very much for your reply!
I wonder if the flow can start from Workflow not from UserService.
E.g.,
1. Browser requests with UserSignup event (or API gateway receives it, do not call UserService but emits event)
2. Workflow receives the event, then calls UserService.signupUser activity
3. UserService creates a user then return the call back to Workflow
4. Workflow resolves the call(singupUser) then calls EmailService.sendEmail
5. EmailService.sendEmail sends an email then calls back to Workflow
6. Workflow resolves the call(sendEmail) then the flow is completed
The difference is that Every workflows will be defined inside Workflow and Services won't serve requests directly, which I believe this gives a complete view to the flow.
However there must be something that I'm missing here since what I'm describing seems like an anti pattern.
It's certainly acceptable to start workflows explicitly! However it wouldn't be a good fit for the user signup process.
In the above example, the user just wants to signup. They don't care about receiving a welcome email or being subscribed to a mailing list or anything else, they just want to register an account. That's a pretty good use case for just `POST /signup`, that hits the user service and spits out an event that the user has signed up.
Starting a new workflow when that event is published makes sense in this case.
An example when a workflow is started explicitly could be something like doing a fire system test. You could:
1. shoot off a command that starts the FireSystemTestWorkflow
2. the workflow sends a bunch of commands to test sensors and sirens
3. those things publish events that they're functioning correctly
4. the workflow waits for all of these events to come back
5. the workflow publishes a FireSystemTestedSuccessfully event
The nice side of this is that the workflow can respond if a sensor or siren fails and does what's called a "compensating action", ie: compensates for the deviation of the successful path by performing a corrective action like sending a command to start the device or notify a technician.
Wow. Thanks for the extra explanation about when the different approach can benefit.
I love you. Will definitely give bus-workflow a thorough shot.
And a very last question if you could spare a bit more time..
Again the user signup & event flow,
When Workflow calls EmailService.sendEmail (given that the communication is via RPC and EmailService.sendEmail is an async operation that will resolve if the email was sent successfully), should Workflow wait for the sendEmail operation to resolve and complete the flow?
Or should EmailService dispatches an event EmailSent so that Workflow can complete the flow?
This is a bit off the topic but I've been sticking with RPC style call rather than Events but still don't know yet what the best practice is.
