heartbeat.js

const cluster = require('cluster');
const minions = ['alpha', 'beta'];
const tHeartBeat = 1000
const tCheck = 1000
const tTimeout = 3000

if (cluster.isMaster) {
  for (let id of minions) cluster.fork({id});

  let lastHeartbeat = {}
  cluster.on('message', (worker, {id}) => {
    console.log(`receive heartbeat from ${id}`)
    // record last heartbeat time
    lastHeartbeat[id] = Date.now();
  })

  // health check scheduler
  setInterval(_ => {
    let now = Date.now()
    console.log('check', lastHeartbeat)
    for(let id of minions){
      if(lastHeartbeat[id] + tTimeout < now){
        console.log(`worker ${id} is dead`)
      }
    }
  }, tCheck)

} else {
  let id = process.env.id
  console.log(`minion ${id} started`)
  let startTime = Date.now()
  setInterval(_ => {
    if(id !== minions[0] || Date.now() < startTime + 3000) process.send({id})
  }, tHeartBeat);
}