Nginx upstream health check - custom header
Like every other use of proxy_pass nginx defaults to making an HTTP/1.0 connection to the upstream with the Host header set to the defined name of the upstream or its IP address.
You can set a Host header or HTTP/1.1 (or both) yourself to override these.
location /health {
health_check;
proxy_pass http://backend;
proxy_http_version 1.1;
proxy_set_header Host $host;
}