HA Backend rule help

[planetinse]

I want to check http response on Server "A"
If i get a 200 response there I would like customer to proceed
to Server "B" - if Server B is down - throw a 503 error page.
likewise if Server "A" responds 503 i want to throw 503 page

so its basically two servers need to respond OK for the routing to happen.

how can i make a rule like that?