nginx return http code 498

[jonefee]

i am using nginx as a reverse proxy server(Let 's call it Server A). server
A's upstream server is also a nginx server((Let 's call it Server B) backend
with a jetty server((Let 's call it Server C) served at port 8080.  we have
a lot of Server A and each one of them use the same bunch of server B as
upstream, each server B use its local jetty server as its own upstream
server. server A and Server B work at port 80.

i found few http response code 498 from server B about 2 or 3 days ago . 
google on it found little information ,any one has some idea ?

server A config:

   location /views/3.0/ {

        if ( $query_string ~* ^(.*)req_times=[2-3](.*)$ ){
            return 444;
        }
        proxy_pass http://views_java_sec_cnc;
        proxy_set_header        REMOTE_ADDR       $remote_addr;
        proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;

        proxy_next_upstream http_500 http_502  http_504;
        limit_req   zone=java  burst=5 nodelay;
        proxy_next_upstream_tries 1;

    }

Server B config:

 # views
    location /views/ {
        proxy_pass          http://views_server;
        proxy_redirect      off;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header    X-Real-IP $remote_addr;
        proxy_http_version  1.1;
        proxy_set_header    Connection "";
        #proxy_pass_request_body off;
        #proxy_cache         IFACE;
        limit_req   zone=views-java  burst=5 nodelay;
    }

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,263399,263399#msg-263399