So I opened my site yesterday night. Shock. 502 error. I tried all of my sites, and my sister's site (that I'm currently hosting on the same server) and all of them displayed the same message.
502 - Bad Gateway
ngix version ???
I wasn't shocked, but it was rather inconvenient because I was in the middle of posting my resolutions post for the year. The reason I wasn't shocked was because I've had the same error before, and it resolved itself. That time, I just logged in through FTP to check that the sever wasn't really down or something (it wasn't), refreshed the sites, and it worked again! This time around I tried reloading pages for about 15 minutes before I gave up and went to bed, thinking that the site should be back up and running in the morning. It was.
Still, I'd rather this didn't happen. Since I'm on a Shared server I don't have much control over the server settings myself, so I can't perform any of the many tweaks that users around the net have found to resolve this error. What can I do? Contact the host, obviously. Let's see what they have to say about this...
UPD: Problem solved, I think, see this post.