如何排查 nginx 访问日志里的 400 响应码？

[wdoc]

就是每分钟有一条来自自己其它服务器公网 IP 的访问记录，看不出哪里的问题，有人遇到这种问题吗？

47.100.xxx.xx - - [22/Feb/2023:09:08:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:09:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:10:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:11:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:12:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:13:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:14:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:15:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:16:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:17:32 +0800] "" 400 0 "-" "-"
47.100.xxx.xx - - [22/Feb/2023:09:18:32 +0800] "" 400 0 "-" "-"