how I can wait explicitly for an output if it's not a straight dependency o a resource? https://gist.github.com/MattBlack85/8fc884341cbc85d9dc0252286fb3c938 at line 37 I need the elastic IP value that I have to inject into the instance init script

you’ll want to flip it the other way:

user_data=api_ip.id.apply(lambda x: rendered % ('foo', x))