I'm configuring my server to run node.js as a daemon. I've setup Upstart to handle startup and shutdown of node, which works wonderfully. The next step is to make sure that node.js is restarted if it dies. A few of the guides have suggested using Monit (or Fugue) to monitor the process (in Monit's case by doing an HTTP request to the server and waiting for a response).
I'm happy to use something like Monit or Fugue, but I'm not sure why one wouldn't (or couldn't) just use Upstart's respawn feature. I assume Upstart will monitor the PID of the launched process and just kick it off again if it dies. What does Monit or Fugue give you that Upstart doesn't?
Given that Upstart just checks the PID, a tool like Monit that makes an actual request will provide you an answer of app sanity more faithfully. A process may happily be running but stuck in some way such that it is not serving requests.