Is there a callback for when a flow starts? I see there are callbacks for on_completion and on_failure

Hey jack - there isn't right now; could you describe what you would use such a callback for vs. introducing a few additional lines at the beginning of your flow function?

We are using the

on_completion

and

on_failure

callback to point to a function

send_slack_message

We wanted the same functionality for

on_start

, but since it doesn't exist yet, I've added these lines at the top of the flow to manually call

send_slack_message

using the same signature as when the callback happens.

context = get_run_context()
    send_slack_message(context.flow, context.flow_run, context.flow_run.state)

It would be tidier for this use case if the

on_start

callback worked. It seems odd to call a callback manually. With prefect v1 we used the same callback for any state change. Then we got slack messages for retries as well.