I looked into the sample - it seems this is like calling pulumi via the cmdline. but how would I know when pulumi actually starts to update? if I send my notification "saying update in progress, service down" before calling pulumi, then the notification is sent a lot earlier than need be because first pulumi does all the preparatory work (in my case that's not insignificant because a number of docker images are built) and only then it actually hits the cloud resources.