overleaf/services/document-updater/test/cluster_failover/js/test_pubsub_failover.js

let sendPings
const redis = require('@overleaf/redis-wrapper')
const rclient1 = redis.createClient({
  cluster: [
    {
      port: '7000',
      host: 'localhost',
    },
  ],
})

const rclient2 = redis.createClient({
  cluster: [
    {
      port: '7000',
      host: 'localhost',
    },
  ],
})

let counter = 0
const sendPing = function (cb) {
  if (cb == null) {
    cb = function () {}
  }
  return rclient1.publish('test-pubsub', counter, error => {
    if (error) {
      console.error('[SENDING ERROR]', error.message)
    }
    if (error == null) {
      counter += 1
    }
    return cb()
  })
}

let previous = null
rclient2.subscribe('test-pubsub')
rclient2.on('message', (channel, value) => {
  value = parseInt(value, 10)
  if (value % 10 === 0) {
    console.log('.')
  }
  if (previous != null && value !== previous + 1) {
    console.error(
      '[RECEIVING ERROR]',
      `Counter not in order. Got ${value}, expected ${previous + 1}`
    )
  }
  return (previous = value)
})

const PING_DELAY = 100
;(sendPings = () => sendPing(() => setTimeout(sendPings, PING_DELAY)))()