Cloud events to be publlished when workflow status change

[fjtirado]

Possible workflow status are defined in the specifcation. However, there is not information of the content of the cloud event that very likely any implementation might publish when status is changed.

What would you like to be added:
Common content of the cloud events to be published when a status is changed

Why is this needed:
To make it possible users of any implementation to rely on the common content when listening to a status phase change event.

[fjtirado]

The first thing (my guess) that we should decide is between:

1. Publishing a different event type per status phase: started, aborted, complete...
2. Publishing the same event type (StatusChangeEvent) and include the old and the new status, preferably as cloud event attributes
3. Other ;)

It is easier to consume different event types by another workflow (you just put the type on the event task) while using attributes requires filtering of those attributes (if they are cloud event attributes, there wont be need to deserialize the data to perform the filter, at least theoretically)

Regardless the decision on that question, my bet is that, besides the status itself, we should include the workflow name plus the current input and context (if context is large, the event will be potentially huge, I guess that we can let implementors to leave that configurable)

[cdavernas]

I'd definitly go for your first suggestion, which makes routing/processing easier and more compliant with the Cloud Event Spec: the payload of the events should be opaque to those concerns.

If required, though, we could also add a Workflow/Task Status Changed event, used by "lazy" consumers to reflect status changes (it would be a kind of duplicate of other events, but with a simplistic payload limited to status).

As for the events types, I'd recommend using the following:

Type	Description
io.serverlessworkflow.workflows.started.v1	Notifies about the start of a workflow instance.
io.serverlessworkflow.workflows.suspended.v1	Notifies about suspending a workflow instance execution.
io.serverlessworkflow.workflows.resumed.v1	Notifies about resuming a workflow instance execution.
io.serverlessworkflow.workflows.cancelled.v1	Notifies about the cancellation of a workflow instance execution.
io.serverlessworkflow.workflows.faulted.v1	Notifies about a workflow instance being faulted.
io.serverlessworkflow.workflows.completed.v1	Notifies about the completion of a workflow instance execution.
io.serverlessworkflow.workflows.correlation-started.v1	Notifies about a workflow instance starting to correlate events.
io.serverlessworkflow.workflows.correlation-completed.v1	Notifies about a workflow instance completing an event correlation.
io.serverlessworkflow.tasks.started.v1	Notifies about the start of a task.
io.serverlessworkflow.tasks.suspended.v1	Notifies about suspending a task's execution.
io.serverlessworkflow.tasks.resumed.v1	Notifies about resuming a task's execution.
io.serverlessworkflow.tasks.cancelled.v1	Notifies about the cancellation of a task's execution.
io.serverlessworkflow.tasks.faulted.v1	Notifies about a task being faulted.
io.serverlessworkflow.tasks.completed.v1	Notifies about the completion of a task's execution.

[fjtirado]

@cdavernas Ill open PR to incorporate your proposal to the spec, thanks a lot!!!

[cdavernas]

@fjtirado Are you still on it? Otherwise I can do it if you prefer ;)

[fjtirado]

@cdavernas Hi, please go ahead, thanks a lot!