I had a look at the link. I do not really understand what it does (I work in IT, many years as a sysadmin) but it suspiciously looks like my code on a day I thought I had a revolutionary idea.
Then a few weeks later I have to look at it again and try to rediscover that revolutionary idea while the family is waiting for the lights to work again.
It's basically: query the database for the list of nodes, then tell the LB which of those nodes you want to send traffic to. Something you come up with in 5min if you ever need it.
Debugging I guess? If you have more logic in your LB/routing, you may want to process all of it as usual, but skip the random selection part and talk to a specific server for a single request. Or it could be used for pull-style monitoring over the same LB as traffic (GET /stats/i-0001234). Or some weird cluster selection... like HP uses numbers in the domain, for example www8.hp.com
Then a few weeks later I have to look at it again and try to rediscover that revolutionary idea while the family is waiting for the lights to work again.