Tonight's issue had nothing to do with cloudflare.
The message being presented to all visitors was:
Website currently unavailable
The website you are trying to access is currently unavailable. Please try again at a later time.
If you are the site owner, here is a help resource to help resolve the issue.
This means cloudflare was unable to connect to our server, in this case because we were down.
I was notified of the problem but was unable to connect for some hours to diagnose, after finally gaining access it appears the server ran out of memory and as a result lost network connectivity sporadically, even when it was returning pings it was unable to accept http connections due to the memory issue.
I am still going through the logs to determine the root cause of the problem - moodle.org receives hundreds of hits every minute so looking for anomalies is fairly time consuming, especially when even I am unable to access the server.
I will post a follow up later today, its currently 4am and my immediate goal is to get the server back up and running.
Thank you for your patience.