How do I detect if a pool is down in an iRule?

Not that you don't have valid questions, because they're good ones, but wouldn't it be easier to just check to see if the pool is down prior to sending the request to it? If all you're looking to do is redirect when no members in the pool are available, something like this would work:

when HTTP_REQUEST {
  if { [active_members your_pool] < 1 } {
    HTTP::redirect "http://somedomain.com/somepage.html"
  } else {
    pool your_pool
  }
}

I know it doesn't answer your questions (which I'd love to do, when I get a minute to look into them), but I would think it would give you the desired behavior, no?

Colin