Can i bring a webpage (node) up/down using irules?

Agree with all comments above, however to answer the question regarding an iRule to perform this function, there a command LB::DOWN which marks the currently selected pool member down, however the result of this is that the monitor is immediately fired and if all is well will bring the node back up again immediately.

We do what Arie suggested above, and change the contents of a file /platform/mode.jsp from "normal" to "maintenance" (for a hard shutdown) and "transition" (for a soft shutdown);-

ltm monitor http bpweb_http_mode.jsp {
    defaults-from http
    interval 5
    recv "normal"
    recv-disable "transition"
    send "GET /platform/mode.jsp\r\n\r\n"
    time-until-up 0
    timeout 16
}