WebSocket NGINX/NODEJS stickiness Issue - node.js

Question

I'm writing web socket project, everything is working like expected(locally), I using:
NGINX as a WebSockets Proxy
NODEJS as a backend server
WS as websocket module: ws
NGINX configuration:
map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}
upstream backend_cluster {
server 127.0.0.1:5050;
}
# Only retry if there was a communication error, not a timeout.
proxy_next_upstream error;
server {
access_log /code/logs/access.log;
error_log /code/logs/error.log info;
listen 80;
listen 443 ssl;
server_name mydomain;
root html;
ssl_certificate /code/certs/sslCert.crt;
ssl_certificate_key /code/certs/sslKey.key;
ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2; # basically same as apache [all -SSLv2]
ssl_ciphers HIGH:MEDIUM:!aNULL:!MD5;
location /websocket/ws {
proxy_pass http://backend_cluster;
proxy_http_version 1.1;
proxy_redirect off ;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
}
}
Like I mentioned this is working just fine locally and in one machine in development environments, the issue I'm worry about is when we will go to production, in production environments will have more that one nodejs server.
In production the configuration for nginx will be something like:
upstream backend_cluster {
server domain1:5050;
server domain2:5050;
}
So I don't know how NGINX solves the issue for stickiness, meaning how I know that after the 'HANDSHAKE/upgrade' is done in one server, how it will know to continue working with the same server, is there a way to tell NGINX to stick to the same server?
I hope I make my self clear.
Thanks in advanced

Answer 1

Use this configuration:
upstream backend_cluster {
ip_hash;
server domain1:5050;
server domain2:5050;
}

Answer 2

clody69's answer is pretty standard. However I prefer using the following configuration for 2 reasons :
Users connecting from the same public IP should be connecting to 2 different servers if needed. ip_hash enforces 1 server per public IP.
If user 1 is maxing out server 1's performance I want him/her to be able to use the application smoothly if he/she opens another tab. ip_hash doesn't allow that.
upstream backend_cluster {
hash $content_type;
server domain1:5050;
server domain2:5050;
}