How to solve the issue with proxy_set_header host $host in nginx?

If you encounter an issue with the proxy_set_header host $host directive while using Nginx’s proxy module, there are several possible solutions:

1. Check for grammar errors: Make sure that the syntax in the Nginx configuration file is correct, such as ensuring that the statement “proxy_set_header host $host” is not missing a semicolon (;) or placed incorrectly.
2. Check if the module is enabled: Confirm if Nginx has been compiled and enabled with the proxy module, you can use the command nginx -V to check the compiled module configuration information.
3. Check the version of Nginx: the proxy_set_header directive was introduced in Nginx version 1.1.4. If you are using an older version of Nginx, it may not support this directive. You can try upgrading to a higher version of Nginx.
4. Check the $host variable: The $host variable is one of the built-in variables in Nginx, representing the value of the Host header of the client request. Make sure the Host header in the request is correctly set, otherwise the $host variable may be empty.
5. Check the configuration of the proxy target: If you are using the proxy_pass directive to proxy requests to another server, make sure the configuration of the proxy target server is correct and can properly handle the Host header in the requests.

If none of the above methods are able to solve the problem, more specific error information and Nginx configuration can be provided to accurately identify and resolve the issue.