当出现下面这行命令行输出时，Nginx相当于启动失败，新配置文件未生效：

root@nginx-deployment-6686f596f-xhjt8:/etc/nginx/conf.d# nginx -t
2020/09/17 06:00:56 [emerg] 115#115: host not found in upstream "nginx2-deployment" in /etc/nginx/conf.d/default.conf:2
nginx: [emerg] host not found in upstream "nginx2-deployment" in /etc/nginx/conf.d/default.conf:2
nginx: configuration file /etc/nginx/nginx.conf test failed

如果新的配置文件生效，当Nginx连接nginx2-deployment时，在接收到RST报文、发生超时等，会重新选择到127.0.0.1:80这台server。

用body_filter_by_lua指令实现成本较小，参见https://github.com/openresty/lua-nginx-module#body_filter_by_lua，注意这会降低Nginx的转发性能，如果能在上游应用服务器上做更好