This isn't the first spam/DDOS attack on HN, although it's one of the more severe. This is basic stuff for any kind of user-driven forum, going back to the BBS days. You are going to have periodic problems with trolls and spammers so you need to have some sort of mitigation process in place. That doesn't need to be some sort of top-heavy new technology, it can be as simple as the ability to add a few new scripting rules or wildcard matches on a few minutes notice, or hit the pause button on new account creation.