upstream server {
    server localhost:3000;
}

server {
    # запускаем на дефолтном порту
    listen 80 ipv6only=on;
    listen [::]:80 ipv6only=on;

    # адрес привязанного домена к IP сервера
    server_name example.com;

    charset utf-8;

    location / {
        # именно http://server, т.к. мы запустили upstream с названием server (в самом верху)
        proxy_pass http://server;
        proxy_redirect off;
        proxy_http_version 1.1;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header Authorization $http_authorization;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}