Our web server stopped functioning around 12:20PM today (August 28th 2015).
I was unable to login to the machine to assess what was happening. Whatever it was saturated disk I/O and ftp which is on the same machine continued to function but ssh and vnc did not.
The logs did not provide any useful details to isolate the cause. I have not seen this behavior in this machine previously.
There were a number of recent updates. Also I added two more gigabytes of RAM for a total of ten instead of eight.