send socket broadcast to other server with nginx

Question

i try to implement a user online list in my chat application. for the first i used one server instance, now im working with an nginx server and tree server instances. when i try to display my online users, i cant display via the sockets to other clients, that are on another server instance.

docker-compose.yml:

version : '3.2'

services:

  redis:
    image: redis:alpine
    ports:
      - "6379:6379"
    networks:
      - chatnetworks

  nginx:
    image: nginx:alpine
    volumes:
      - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro
    build:
      context: .
      dockerfile: ./DockerfileNginx 
    volumes_from:
      - nostromo
      - millennium_falcon
      - spaceship_enterprise
     
    ports:
      - "4001:4001"

    networks:
      - chatnetworks
    
  
   

  userdb:
    image: mongo:latest 
    container_name: mongodb
    volumes:
      - userdb:/data/db
    networks:
      - chatnetworks

  prometheus:
    image: prom/prometheus:latest
    container_name: prometheus
    ports:
      - 9090:9090
    volumes:
      - ./prometheus:/etc/prometheus
      - prometheus-data:/prometheus
    command: --web.enable-lifecycle  --config.file=/etc/prometheus/prometheus.yml
    networks:
      - chatnetworks

  grafana:
    image: grafana/grafana:latest 
    container_name: grafana
    restart: always 
    volumes: 
      - ./grafana/grafana.ini:/etc/grafana/grafana.ini
      - ./grafana/provisioning:/etc/grafana/provisioning
      - ./grafana/data:/var/lib/grafana
    user: "1000"
    ports:
      - 3000:3000
    networks:
      - chatnetworks

  nostromo:
    build:
      context: .
      dockerfile: ./Dockerfile 
    ports: 
      - '4000'
    restart: 'on-failure'
    networks:
      - chatnetworks  
    depends_on: 
      - redis
   
    environment: 
      - APPID=Nostromo


  millennium_falcon:
    build:
      context: .
      dockerfile: ./Dockerfile 
    ports: 
      - '4000'
    restart: 'on-failure'
    networks:
      - chatnetworks  
    depends_on: 
      - redis
 
    environment: 
      - APPID=Millennium_Falcon


  spaceship_enterprise:
    build:
      context: .
      dockerfile: ./Dockerfile 
    ports: 
      - '4000'
    restart: 'on-failure'
    networks:
      - chatnetworks  
    depends_on: 
      - redis
    environment: 
      - APPID=RaumschiffEnterprise


volumes:
  userdb:
  prometheus-data:
 
networks:
  chatnetworks:

server.js (part):

ocket.on('user-connected',(userName_)=>{
        //console.log(userName_ + " joined " +socket.id)
        
        //save the time when a user connected
        startTime = new Date()
        

        
        //push username and socket.id into array to display users in chat client
        arrayUsers.push({
            socket_id: socket.id,
            userName_socket: userName_,
            startTime_: startTime 
        })
        
        //console.log(arrayUsers.length)
        //console.log(arrayUsers.startTime_)

        

        //increment metric
        useravailable.inc(1)
   
        console.log(arrayUsers)
        
        //client message for users that a new user joined
        socket.broadcast.emit('user-connected',userName_)
        
        //update online-users list
        socket.emit('online-users',arrayUsers)
        socket.broadcast.emit('online-users',arrayUsers)

    })

index.html (part, client):

socket.on('online-users',(arrayUsers)=>{
 
    let arrayUserNamesOnline=[]
    arrayUsers.forEach(elem=>{
        arrayUserNamesOnline.push(elem.userName_socket)
        
    })


    alert("users online: " +arrayUserNamesOnline)

    appendUser(arrayUserNamesOnline)
    //arrayUserNamesOnline.splice(0,arrayUserNamesOnline.length)

})

function appendUser(arrayUserNamesOnline){

    userArea.removeChild(userArea.lastElementChild)
    
    let mainDiv = document.createElement('div')

    var markup=`
        <h4>${arrayUserNamesOnline}</h4>
        
        
    `
    mainDiv.innerHTML=markup
    userArea.appendChild(mainDiv)
    
}

is there a way to make the arrayUsers array for every server instance available, i think the problem is that my clients are connecting to the different servers, so i need to interconnect them, but i dont know how i can make the array changeable for every server container.