Thanks! This could be a solution. But to be honest, I was actually hoping that the automatic redirection could be done with something as simple as an entry in iptables.

Incidentally, what do you think about dynamic favicons [1]? They're a fairly simple feature to implement, but a useful one. In your case, they'd let otherwise-useless favicons be status indicators themselves (which makes sense for anyone opening/refreshing a tab anyway) if they so chose.

Plus, it'd let your users promote their branding (upvote/downvote icons in that specific case) which is a win-win.

At minimum, some custom title text ('[user's main offering] is up'/'down' etc) would make a lot of sense, but I really think the favicons are simple enough (both to implement and to understand) and visible enough to be worth it too - it'd allow for at-a-glance uptime information [2].

[1] http://www.reddit.com/r/ideasfortheadmins/comments/36w2s3/ha...

[2] http://i.imgur.com/Ifyn1PF.png