You don't need a proxy. Just using an intervening Firewall/Router should do the trick. Basically, if your Master is connecting to slaves across the Internet, the JNLP3 logic will have problems.
You should be able to replicate via:
Master <=> Firewall/Router <=> Internet <=> Firewall/Router <=> multiple slave machines.
Or, more simply:
Master <=> Network <=> Firewall/Router <=> Slaves.
The idea is that the Firewall/Router will NAT the IP addresses of the slaves to one IP address, and the Master, seeing multiple slaves connecting via the same IP address, will get confused.
Slave IP addresses:
NAT firewall / Router:
Private IP <=> Public IP
192.168.10.1 <=> 184.108.40.206 port 100
192.168.10.2 <=> 220.127.116.11 port 200
192.168.10.3 <=> 18.104.22.168 port 300
Converts all private IP addresses of the slave machines (behind the
firewall) to the publicly routeable IP address that firewall uses to connect to the Internet.
Or any other intervening network.
Will see three different slaves try to connect with the same IP address
(22.214.171.124) and different NAT ports.
Master will get confused.
I hope this helps.
I have slaves that are on a remote network, across the Internet, with an intervening Firewall/Router, and JNLP3 did not work. JNLP2 works fine with that configuration.
I'll create a simple test to replicate.