Nginx-specific HTTP status code: 499

rfc2616 defines 400-417 error codes, and 418-499 is a custom category. So it can be judged that 499 is defined by nginx itself.
When analyzing nginx logs, sometimes 499 errors are found, which do not exist in apache logs, so I feel very confused. View related documents

Check the nginx source code and you will find the following explanation about the nginx code
# vim src/http/ngx_http_special_response.c
……………………………..
ngx_string(ngx_http_error_495_page), /* 495,
https certificate error */
ngx_string(ngx_http_error_496_page), /* 496,
https no certificate */
ngx_string(ngx_http_error_497_page), /* 497,
http to https */
ngx_string(ngx_http_error_404_page), /* 498,
canceled */
ngx_null_string,
/* 499, client has closed connection */
…………………………………………… …………..

It can be seen from the above explanation that the 499 code is likely to be caused by the server processing the request for too long, and the client disconnected because it could not bear it.