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。

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
root@nginx-deployment-6686f596f-xhjt8:/etc/nginx/conf.d# more default.conf
upstream test_upstream {
server nginx2-deployment;
server 127.0.0.1:80 backup;
}

server {
listen 80;
server_name nginx-test.ingageapp.com;

#charset koi8-r;
#access_log /var/log/nginx/host.access.log main;

location /admin {
proxy_pass http://test_upstream;
}

@陶辉

可以将serviceB后加入backup选项，例如：

upstream test_default {

    server serviceA;

    server serviceB backup;

}

注意，不要使用hash类负载均衡算法，使用roundrobin、least conn等复制类扩展算法才有效。

另外，注意不要关闭next_upstream功能，而且http响应码、error、timeout已经配置到next_upstream中了。