Maintence

I might suggest you use a class/datagroup. That way you can dynamically update the class with hosts/uris that are offline and then you don't have to change the rule.

IE:

when HTTP_REQUEST {
   if { [matchclass [HTTP::host] equals $::offline_hosts] or \
        [matchclass [HTTP::uri] starts_with $::offline_uris] } {
      HTTP::redirect http://www.domain.com/offline
   }
}

You can then manage the offline_hosts and/or offline_uris datagroups via the GUI or iControl and it will dynamically take effect.

You can also use priorities to specify that this rule always runs first.

To do that, you add a priority statement with a number between 1-1000.

If you add the statement before the when statement, then that is the default priority for all subsequent when statements. IE:

priority 250
when HTTP_REQUEST {
}

You can alternatively specify the priority after the event name in the when statement. In this case, the priority is changed only on that event. IE:

when HTTP_REQUEST priority 250 {
}

This will make sure the this rule event runs before any other rule event with higher numbered priority. The default priority is 500.