penbw (pen backend watcher) is a small addon for pen, a high-availability load balancer for TCP. penbw monitors and blacklists a (http-)backend automatically in case of a failure. pen itself is able to detect if a backend is down and will blacklist it on the fly. But if, for example, the backend is still accepting connections and simply sending back bogus or nothing, pen will not detect that, as pen doesn't care about application-level protocols. By contrast, penbw will be effective in such a situation.
