Name
 ngx_http_upstream_dynamic_module
 This module provides the functionality to resolve domain names into IP addresses in an upstream at run-time. 
 It comes from Taobao Tengine @ http://tengine.taobao.org

Synopsis

    upstream backend {
        dynamic_resolve fallback=stale fail_timeout=30s;

        server a.com;
        server b.com;
    }

    server {
        ...

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

Notes

 It is a tengine module from
 https://github.com/alibaba/tengine/blob/master/src/http/modules/ngx_http_upstream_dynamic_module.c
 and made to work with nginx 1.9
 It follows original tengine license.