Comment by zaneb for Ceilometer (in the past, now it's actually Aodh) calls whatever URL you ask it to. The URL that the Heat autoscaling resources provide (via the signal_url attribute) is for the resource signal API.

Yes, IIRC just change the alarm to OS::Aodh::Alarm and the attribute from alarm_url to signal_url to do it the modern way. I think there's enough backward compatibility code that the example will work as is for now too.