redirect to new path

In that case, you could try something like this:

when HTTP_REQUEST {
     Check the requested path with wildcard matching
    switch -glob [HTTP::path] {     
        "/site1/online/*"  {
             Trim the "/site1" from the front of the path
            HTTP::path [string range [HTTP::path] 6 end]

             Update the pool
            pool 192.168.111.90
        }
    }
}