参考：
https://blog.csdn.net/weixin_30835933/article/details/97707016

用nginx反向代理后端接口，前端显示502，查看nginx日志，显示
解决nginx访问问题connect() to 127.0.0.1:8080 failed (13: Permission denied) while connecting to upstream,.

处理办法：
解决步骤：
关闭selinux
[root@localhost ~]# getenforce
Enforcing
[root@localhost ~]# setenforce 0
[root@localhost ~]# getenforce
Permissive