Sample (and simple) NGINX configuration as a load-balancer, using SaltStack's peer communication to retrieve list of backend servers.

gistfile1.nginxconf

# /srv/salt/shared/nginx/files/sites-available/default.lb
upstream app_nodes {
    # Build list of backend servers
    # using peer communication as the mine is cached and slow to pick up new hosts
    {% for server,ips in
        salt['publish.publish'](
            'G@roles:appnode',
            'network.ip_addrs', expr_form='compound').items() -%}
    #   host: {{ server }}
    {% for ip in ips -%}
    server {{ ip }}:80 ;
    {% endfor -%}
    {% endfor -%}
}

server {
  listen 80 default_server;
  server_name {{ realm }}.example.com www.{{ realm }}.example.com;

  error_log /var/log/nginx/default/error.log;

  location / {
    proxy_pass http://app_nodes;
  }
}

gistfile2.yml

# /srv/salt/shared/nginx/init.sls
/etc/nginx/sites-available/default:
  file.managed:
    - source: salt://shared/nginx/files/sites-available/default.lb
    - template: jinja
    - require:
      - pkg: shared.nginx