collectd/files/collectd_nginx.conf

{%- if salt['pillar.get']('nginx:server:site:nginx_stats_server') %}
{%- set stats_server = salt['pillar.get']('nginx:server:site:nginx_stats_server') %}

LoadPlugin nginx
<Plugin "nginx">
  URL "http://localhost:{{ stats_server.host.port }}"
</Plugin>

{%- endif %}