Then, I don't understand
Falko, I can't realize what is going on. As I said I have 2 wordpress (wp1 & wp2) running on backend servers and one server acting as primary (wp), balancing requests.
As you know wordpress has a login procedure with session and cookie. My primary server is balancing between backend servers and is keeping the session!!
Now my browser is logged on wp1. If page is reloaded then I will be in wp2 and also logged. It's easy to see the alive session because I can access to site admin (link) whatever I were wp1 or wp2. If I log out then in both WP's there's no site admin link but login link
Still more. Let's try
I'm going to stop wp2 (now I'm on it) server while I'm logged: Ok, wp jumps to wp1 with the session alive because wp2 is down. 1 minute and wp2 will be up, then wp should to jump to wp2 and the session should be there.... Ok, wp2 is up and I wp is switching between wp1 & wp2 with the session.
Let's try with wp1. Session logged. wp1 down, working with wp2. 1 minute later wp1 is up and wp is switching between 2 backend servers with the session still alive.
How do you explain that?