While upgrading EC2 servers behind an AWS Elastic Load Balancer (ELB) I noticed that the nginx error log was reporting that my health-check was getting molested. Here is the simple curl test showing the 200 result. The error message, then the solution follow.
$ curl -I localhost/ELB-health-check
HTTP/1.1 200 OK
Server: nginx
Date: Sun, 06 Nov 2022 16:59:46 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 105