负载均衡常见错误

如果后端服务器返回报错，负载均衡仍然会将请求分配到出错的web服务器，
因为负载均衡只会根据调度算法将请求分配到后端，不会进行判断后端是否正常

Syntax:    proxy_next_upstream error | timeout | invalid_header | http_500 | http_502 | http_503 | http_504 | http_403 | http_404 | http_429 | non_idempotent | off ...;
Default:    proxy_next_upstream error timeout;
Context:    http, server, location

[root@lb01 ~]# vim /etc/nginx/conf.d/zh.conf 
upstream zh {
    server 172.16.1.7:80;
    server 172.16.1.9:80;
}

server {
    listen 80;
    server_name linux.zh.com;

    location / {
        proxy_pass http://zh;
        include /etc/nginx/proxy_params;
        proxy_next_upstream http_502 error timeout;
    }
}