Discourse Server Suddenly Refusing SSL Connections

Today it appears my discourse install stopped allowing SSL connections…
I found out while troubleshooting this page I was getting from cloudflare…

Somewhere in the middle of the day Cloudflare started to display a 521 error for our Discourse forums. However they were still accessible via the source IP. So the host was up in the strict sense, at least to requests from my own browser.

Up until today I’ve had the site configured with “Full SSL” in cloudflare, I had to back this down to “flexible”. Once I did that, the forums were reachable again.

Discourse has been set to https only from day 1.
I’ve toggled between full SSL and flexible and have been able to repeat the problem.

Any ideas what might be causing this, or how I could go about looking at logs to see if connections from cloudflare were being rejected by my Discourse server?

I just realized that when I was able to pull up the site earlier via IP, that was a http connection.
When I try ssl\443, I get connection refused.

Is “Flexible SSL” the one where Cloudflare doesn’t care about the validity of the cert the origin presents? If so, it seems likely that whatever cert you had installed on the origin expired. This isn’t really a Discourse problem, though; you might get more specialised advice as how Cloudflare is failing via their support team, or their support forum (which, as it happens, runs Discourse too).