Multiple strategies for maintenance page

Your irule is just missing the LB::reselect command. Pool on its own is not enough as the pool has already been selected and tried in the LB_FAILED event.

Some of my configuration requires the same; if the primary pool is down it is necessary to send the traffic to a standby server in a different pool. I do it without a lot of checks in the irule, using standard config instead.

The pool is configured to do a reselect to a different member if a x number of the other members are down.

Then the irule only includes the LB failed event:

when LB_FAILED {
    LB::reselect pool web-noname_standby_pool
    persist none
}