maintenance

You can always get the number of active members in the current pool with the active_members command. Something like this should work for you...

when HTTP_REQUEST {
  if { 0 == [active_members [LB::server pool]] } {
    HTTP::redirect "http://backup_domain/maintenance.html"
  }
}

Then, just disable all members in the pool and the active_members count will go to zero and the redirect will occur.

Keep in mind, that you could also embed a HTML page directly in the iRule and return that with a HTTP::respond. See the "Custom Reporting with iRules" tech tip I wrote a while back...

http://devcentral.f5.com/Default.aspx?tabid=63&articleType=ArticleView&articleId=66

Click here

The only gotcha is that you can't store any images on the BIG-IP, the response will have to be the entire content.

-Joe