nginx server_name based on $hostname

Most variables in nginx only exist at runtime, not during configuration time.

For this reason, most variables cannot be used with the server_name directive. Since $hostname is a constant value, there's an explicit check for exactly $hostname in the server_name handler.

It only allows for the server_name to be set to $hostname, not static.$hostname. You may be able to patch the source to make it support that feature (ngx_http_core_module.c, look for $hostname), but you can't do it with the existing code.