I believe that I set an encryption key for communication between agents as well as use the local certs for RPC over HTTPS.
They join on their private IP.
Jacob Blain Christen

This is a misstatement. I intended to do such but didn’t complete the work. For this to be true one would need to setup an encryption key for secure intra-node Serf communications as well as the HTTPS listener port for secure RPC over HTTPS.