1、通过nginx访问另外一台服务器报错，报错信息如下：

502 Bad Gateway

The proxy server received an invalid response from an upstream server. Sorry for the inconvenience.Please report this message and include the following information to us.Thank you very much!

2、查看上游服务器防火墙，防火墙启动，打开提供服务器端口，访问正常。