Emit st2.generic.actiontrigger when action/wf is requested/scheduled/running

[shusugmt]

SUMMARY

It is better for uses to have choice that st2.generic.actiontrigger be emitted not only on action complete, but when an action or workflow is transitioned into requested/scheduled/running state.

ISSUE TYPE

• Feature Idea

Detail / Background / Motivation

While I was trying to implement a Slack notification at both start and end of the workflow, I noticed that st2.generic.actiontrigger is only emitted when the workflow reaches LIVEACTION_COMPLETED_STATES, which makes me hard to implement a notification for the start of the workflow.

My idea is to use st2.generic.actiontrigger and write a rule that hook state=running|succeeded by criteria, then run a Slack sendMessage action. I think this is the best approach and design because the target workflow that will be notified on start/end is completely separated from any of the notification code. So notification part is like an aspect and we can weave that into any workflow you like by writing a rule. I can clearly keep a separation of responsibility principle. Some examples:

• All those configuration parameters needed for notification like tokens, channels, etc does not exist in the workflow code itself
• The notification rules can even be placed in a different pack and separated from the release cycle of those core workflows (which are tend to be more important than notifications since they do real business logic)
• If you want to weave notification, then you don't need to modify the target workflow. All you need is to write a rule. This makes us easy to add notification to the exchange pack workflows.

This is fairly easy to implement, but an impact to performance needs to be considered. So I think it is better to have a new config parameter and make this feature opt-in, like this.

[Kami]

Thanks for the feedback - I think that's a reasonable feature request (and putting it behind a feature flag / config option is also a good idea).

[cognifloyd]

I believe this is complete with #4315 and #4330.

[Kami]

Yep - thank you.