给几个小站自建个 CDN 缓存，提速下网站。。。

https://www.cnblogs.com/walls/p/9017821.html

https://blog.csdn.net/dengjiexian123/article/details/53386586

http://www.jackieathome.net/archives/411.html

http://nginx.org/en/docs/http/ngx_http_proxy_module.html#example