id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
1982	Zero length UDP packets aren't forwarded to upstreams but a lack of response is still counted as an upstream failure	d0x2f@…		"Using wireshark I can see that zero length packets aren't forwarded to upstreams, but the nginx logs still report an error after 'fail_timeout'.

{{{
2020/05/20 16:46:03 [error] 2046093#2046093: *3 upstream timed out BBB (110: Connection timed out) while proxying connection, udp client: 127.0.0.1, server: 0.0.0.0:1912, upstream: ""127.0.0.1:1812"", bytes from/to client:0/0, bytes from/to upstream:0/0
}}}

More than 'max_fails' upstream errors cause it to be marked as down even though it was never sent any packets.

As a minimal example I have a simple program that just responds to all requests with a static response and with the following nginx config.

If you send a zero length packet (I use `sudo nmap -sU 127.0.0.1 -p 1912`), it will exhibit the bug.

{{{
user nginx;
error_log /var/log/nginx/error.log debug;

events {
  worker_connections 128;
}

stream {
  upstream radius {
    server 127.0.0.1:1812 max_fails=1 fail_timeout=5s;
  }

  server {
    listen 1912 udp;
    proxy_pass radius;
    proxy_timeout 5s;
    proxy_responses 1;
  }
}

http {}
}}}"	defect	closed	minor		nginx-module	1.18.x	fixed	udp, stream, proxy		Linux navi 5.6.10-arch1-1 #1 SMP PREEMPT Sat, 02 May 2020 19:11:54 +0000 x86_64 GNU/Linux	"nginx version: nginx/1.18.0
built with OpenSSL 1.1.1g  21 Apr 2020
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --conf-path=/etc/nginx/nginx.conf --sbin-path=/usr/bin/nginx --pid-path=/run/nginx.pid --lock-path=/run/lock/nginx.lock --user=http --group=http --http-log-path=/var/log/nginx/access.log --error-log-path=stderr --http-client-body-temp-path=/var/lib/nginx/client-body --http-proxy-temp-path=/var/lib/nginx/proxy --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-cc-opt='-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -D_FORTIFY_SOURCE=2' --with-ld-opt=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now --with-compat --with-debug --with-file-aio --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_degradation_module --with-http_flv_module --with-http_geoip_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-mail_ssl_module --with-pcre-jit --with-stream --with-stream_geoip_module --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-threads"