All of the Pies in this system are headless. I can log into the Pi with the development site using the Remote Desktop Protocol, and from that Pi I can log into the worker Pies using SSH.
All the Pies in the cluster use a static IP address. In a larger cluster it would probably be better to set up a DHCP server on the load balancer. The IP addresses used in the cluster are on the 192.168.1.xxx subnet.
For each worker Pi, I set up a 4GB SD card using the latest version of Raspbian. In raspi-config I set the following options: