SSL certs are attached to domain not IP so as long as all back end nodes have the same domain you can install the same SSL cert on each back end node. You can't install a SSL cert on a node balancer sadly, also you have to set up the balancer to operate in TCP mode so you can't get the X-Forwarded-For HTTP header to get the IP of the user (just a warning most people don't notice this until they've already set it up).
