Use UDP multicast to find other nodes.

config :peerage, via: Peerage.Via.Udp, serves: true
  ip: {0,0,0,0},
  port: 45_900,
  multicast_addr: {230,1,1,1}

Will both broadcast and receive node names via UDP on port 45900, and keep track of ones it’s seen in process state. It’s a GenServer, so we let Peerage know it needs to be run and supervised with serves: true.

Peerage.Server periodically calls poll(), which is a client function for the GenServer’s handle_call(:poll, _, state), which returns the seen node names from state.

Only one node can bind the socket, but you can test multiple nodes using docker, like this.

For more info on UDP in Elixir, see this scaleSmall post on multicast UDP in Elixir from 2015, especially the explation of gen_udp’s active: N mode.