通過server_name配置的域名將請求轉到對應的負載均衡伺服器上。（部分場景可能需要在伺服器上配置hosts，增加server_name的域名對nginx IP的配置）

客戶端請求方式：http://[server_name]

例如：

客戶端請求 http://test-server1.com, 在第一段server的location配置中，會將所有請求定向到 upstream test-server1上，包括js、css等。

upstream test-server1 {
    server www.server1.com:8080 weight=5;
    server www.server2.com:
 
8080 weight=3;
}

upstream test-server2 {
    server www.server3.com:8080 weight=5;
    server www.server4.com:8080 weight=5;
}

server {
    listen       80;
    server_name  test-server1.com;
    location / {
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass http:
 
//test-server1;
    }
}

server {
    listen       80;
    server_name  test-server2.com;
    location / {
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass http://test-server2;
    }
}