nginx.conf

worker_processes auto;
worker_rlimit_nofile 500000;

events {
    use epoll;
    worker_connections 1024;
}

http {
    access_log off;
    error_log /dev/null emerg;

    upstream backend {
        server api02:3334;
        server api03:3335;
        keepalive 200;
    }

    server {
        listen 9999;
        location / {
            proxy_buffering off;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_set_header Connection "";

            # Simple requests
            if ($request_method ~* "(GET|POST)") {
                add_header "Access-Control-Allow-Origin"  *;
            }

            # Preflighted requests
            if ($request_method = OPTIONS ) {
                add_header "Access-Control-Allow-Origin"  *;
                add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS, HEAD";
                add_header "Access-Control-Allow-Headers" "Authorization, Origin, X-Requested-With, Content-Type, Accept";
                return 200;
            }

            proxy_http_version 1.1;
            proxy_pass http://backend;
        }
    }
}