|Pathologically Eclectic Rubbish Lister|
This is great solution if you can afford this kind of deployment. I'm really happy user of mod_perl, but this time I didn't really had machines for deployment at all :-)
All I had where 12 machines dedicated to be web kiosks. This is why I'm trying to avoid disk activity. Besides short bursts of CPU activity, which can be controlled by shard size, I won't affect normal usage of machine which are dual core anyway, so I can use only one core if that becomes problem.
In fact, i went so far to require only core perl modules so I can depend only on perl which is standard on Debian installs anyway since packet manager uses it) and ssh (for which I use dropbear).
I also noticed that automatic deployment of new version and restart is somewhat of challenge if you do it by hand, so Sack can push code update to nodes (using cpio over ssh since I don't really have scp or rsync) and re-exec itself.
Which was nice, but re-exec required me to re-feed data onto each node on restart. This is also nice way to get recovery for nodes or some kind of load migration (if one set of machines becomes busy I should be able to move shards to other machines or increase shard size of idle machines). None of that exists yet, unfortunately.
I have looked into messaging solutions, but my preference is to have queue locally (nodes are part of intranet network) and although they do have Internet connectivity, I would love them not to leave intranet.