FRED's webserver has been down for a number of short (~3 minute) periods all day today. Beginning with a few incidents on friday and a few over the weekend, escalating to 24 such incidents today (so far). Apache simply spawns gradually more and more child processes until it exhausts memory on the server, at which point it fails to respond to a probe from FRED's auto-restart monitor. At that point the monitor restarts Apache, and all is well until the next time it fills the available memory.
I may wave a dead chicken over some Apache settings, but since this is suddenly happening with no config changes or significant change in traffic on the site, I'm tempted to just spin up a new EC2 instance and see if that helps. Maybe the current instance is just going bad in some impenetrable way?