SO_REUSEPORT

server.rb

require "socket"

PORT = 1234
server = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM)

# NOTE: Commentting out this line will prevent multiple processes to run at
# once on the same port.
server.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEPORT, true)

server.bind(Addrinfo.tcp("", PORT))
server.listen(0)

loop do
  client, addr = server.accept
  data = client.recv(1024)
  client.send(data, 0)
  client.close
end