We kind of got off topic, I was arguing that if you were concerned about internal systems being down (including your monitoring/alerting) something like pager d

We kind of got off topic, I was arguing that if you were concerned about internal systems being down (including your monitoring/alerting) something like pager duty would be fine as a backup. Even at huge scale that backup doesn’t need to watch everything. I don’t think it’s particularly relevant to this issue with fb. I suspect they didn’t need a monitoring system to know things were going badly.