I have manage my own Ubuntu server (12.04.4 LTS with Nginx) over at DigitalOcean and when I ran the upgrade command tonight (sudo apt-get upgrade) everything went offline.
Instead of websites, I was getting an 502 bad gateway error.
Turns out, PHP updated and fixed a security issue, that then took my websites offline as the server didn’t have access to PHP, or something like that.
It’s all outlined in this StackOverflow question.
The solution is really easy, finding it was the troublesome part.
Hopefully this helps someone who runs into the same issue and is in a panic because their sites are down.