Awesome here. Let me suggest you that instead of

def set_routine
  @routine = Routine.find_by(id: params[:id])
end

You do something like:

def set_routine
  @routine = Routine.find(params[:id])
end

.find_by returns nil when it doesn't found nothing and then you could face NoMethodError for NilClass.

.find raises an exception and you can better handle that with a notification or message or something.