When I was recently talking about load-balancers, and automatically adding back-ends, not just removing bad ones that go offline, I obviously spent a while looking over some.
There are several dedicated load-balancers packaged for Debian GNU/Linux, including:
In addition to actual dedicated load-balancers there are things that can be coerced into running in that way: apache2, varnish, squid, nginx, & etc.
Of the load-balancers I was immediately drawn to both pen and pound, because they have command line tools ("penctl" and "poundctl" respectively) for adding/removing/updating the running configuration.
Pen I've been using for a couple of days now, and although it suffers from some security issues I'm confident they will be resolved in the near future. (#741370)
My only outstanding task is to juggle some hosts around and stress-test the pair of them a little more before deciding on a winner.
In other news I kinda regret the whole blogspam.net API. I'd have had a far simpler life if I'd just ran the damn thing as a DNSBL in the first place. (That's essentially how it operates on the whole anyway. Submit spammy comments for long enough and you're just blacklisted, thereafter.)