Simple server distributes 'action' messages between all connected clients.

redux-socket-server.js

import SocketIO from 'socket.io'

const io = SocketIO(3030)

const history = []

io.on('connection', (socket) => {
  // Replay actions on new clients  
  socket.on('init', (_) => history.forEach(action => socket.emit('action', action)))
  
  socket.on('action', (action) => {
    // Persist actions in memory
    history.push(action)
    socket.broadcast.emit('action', action)
  })
})