We put almost all of our Drupal sites behind the excellent Varnish HTTP accelerator, and it gives us a massive performance boost for most site visitors. However it seems to have a tendency to crash without warning and occasionally just dies, leaving our sites down.
We workaround this issue by using another piece of useful kit, called Monit, that keeps an eye on processes on your server and restarts them if necessary.
Installing and configuring Monit is really simple (these instructions are for a Debian based server):
Installation is simple:
apt-get install monit...