I have 3 apache servers in a cluster using HAProxy. Currently I allow all traffic on the backend IPs between the 3 servers - I thought about only allowing internal packets on the HTTP ports (and the memcached ports) - is this going over the top? Does the security benefit outway the performance impact (is there one?). I understand strengthening the private firewalls between the nodes would only be beneficial if one of the servers was penetrated from the frontend, thereby hindering what an attacker could do internally.
What do you do?