ok this worked:

$ curl -sL https://deb.nodesource.com/setup_4.x | sudo -E bash -
$ sudo apt-get install -y git nodejs build-essential nginx
$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
$ echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list
$ sudo apt-get update
$ sudo apt-get install mongodb-org
$ mongo
use nodebb
db.createUser( { user: "nodebb", pwd: "<Enter in a secure password>", roles: [ "readWrite" ] } )
exit
$ sudo nano /etc/mongodb.conf //uncomment auth = true
$ sudo service mongodb restart
$ sudo nano /etc/nginx/conf.d/yourdomain.com.conf

// copy & paste & edit server_name:

server {
listen 80;

server_name domain.com; location / { proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header Host $http_host; proxy_set_header X-NginX-Proxy true; proxy_pass http://io_nodes; proxy_redirect off; # Socket.IO Support proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "upgrade"; }

}

upstream io_nodes {
ip_hash;
server 127.0.0.1:4567;
server 127.0.0.1:4568;
}

// write out

$ git clone -b v0.9.x https://github.com/NodeBB/NodeBB.git nodebb
$ cd nodebb
$ npm install --production
$ npm start

// finish install from browser: http://server.ip:4567

$ nano config.json

// just insert port line

{
"url": "http://localhost:4567",
"port": ["4567", "4568"],
"secret": "34a78c7d-df06-4d82-9c0b-0a3b528822ec",
"database": "mongo",
"port": 4567,
"mongo": {
"host": "127.0.0.1",
"port": "27017",
"username": "nodebb",
"database": "nodebb"
}
}

// write out

$ ./nodebb restart

// now it works without port, on 2 instances