id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2026	Excessive attempts to reconnect when upstream connection refused	Nuru		"Using the TCP load balancer, when the upstream refuses the connection, Nginx immediately retries without adequate throttling. I am seeing 4,000 retries per second with log entries like:
{{{
2020-08-16T06:21:03.662449141Z 2020/08/16 06:21:03 [error] 78#78: *15771 connect() failed (111: Connection refused) while connecting to upstream, client: 10.105.13.228, server: 0.0.0.0:26808, upstream: ""10.105.0.30:26808"", bytes from/to client:0/0, bytes from/to upstream:0/0
2020-08-16T06:21:03.662452948Z 2020/08/16 06:21:03 [error] 78#78: *15500 connect() failed (111: Connection refused) while connecting to upstream, client: 10.105.13.228, server: 0.0.0.0:26808, upstream: ""10.105.0.30:26808"", bytes from/to client:0/0, bytes from/to upstream:0/0
}}}

This causes a dramatic increase in CPU and Memory usage. I am not sure if the client is retrying that quickly (client is Amazon Web Services Network Load Balancer Health Check), but even if it is, Nginx should throttle upstream connection attempts according to [https://docs.nginx.com/nginx/admin-guide/load-balancer/tcp-health-check/#passive-tcp-health-checks the Passive TCP Health Checks documentation]:

  The default values are 10 seconds and 1 attempt. So if a connection attempt times out or fails at least once in a 10‑second period, NGINX marks the server as unavailable for 10 seconds

See also: https://github.com/kubernetes/ingress-nginx/issues/5425

Configuration excerpt (configuration created by ingress-nginx v0.34.1):
{{{
stream {
        ...

        upstream upstream_balancer {
                server 0.0.0.1:1234; # placeholder

                balancer_by_lua_block {
                        tcp_udp_balancer.balance()
                }
        }

        server {
                preread_by_lua_block {
                        ngx.var.proxy_upstream_name=""tcp-example-26808"";
                }

                listen                  26808;

                proxy_timeout           600s;
                proxy_pass              upstream_balancer;

        }
}
}}}"	defect	closed	major		nginx-core	1.19.x	invalid			Linux ingress-nginx-ingress-controller-pp28p 4.14.181-142.260.amzn2.x86_64 #1 SMP Wed Jun 24 19:07:39 UTC 2020 x86_64 Linux	"nginx version: nginx/1.19.1
built by gcc 9.2.0 (Alpine 9.2.0) 
built with OpenSSL 1.1.1g  21 Apr 2020
TLS SNI support enabled
configure arguments: --prefix=/usr/local/nginx --conf-path=/etc/nginx/nginx.conf --modules-path=/etc/nginx/modules --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/nginx.pid --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug --with-compat --with-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_addition_module --with-http_dav_module --with-http_geoip_module --with-http_gzip_static_module --with-http_sub_module --with-http_v2_module --with-stream --with-stream_ssl_module --with-stream_realip_module --with-stream_ssl_preread_module --with-threads --with-http_secure_link_module --with-http_gunzip_module --with-file-aio --without-mail_pop3_module --without-mail_smtp_module --without-mail_imap_module --without-http_uwsgi_module --without-http_scgi_module --with-cc-opt='-g -Og -fPIE -fstack-protector-strong -Wformat -Werror=format-security -Wno-deprecated-declarations -fno-strict-aliasing -D_FORTIFY_SOURCE=2 --param=ssp-buffer-size=4 -DTCP_FASTOPEN=23 -fPIC -Wno-cast-function-type -I/root/.hunter/_Base/2c5c6fc/d64af22/92161a9/Install/include -m64 -mtune=native' --with-ld-opt='-fPIE -fPIC -pie -Wl,-z,relro -Wl,-z,now -L/root/.hunter/_Base/2c5c6fc/d64af22/92161a9/Install/lib' --user=www-data --group=www-data --add-module=/tmp/build/ngx_devel_kit-0.3.1 --add-module=/tmp/build/set-misc-nginx-module-0.32 --add-module=/tmp/build/headers-more-nginx-module-0.33 --add-module=/tmp/build/nginx-http-auth-digest-cd8641886c873cf543255aeda20d23e4cd603d05 --add-module=/tmp/build/ngx_http_substitutions_filter_module-bc58cb11844bc42735bbaef7085ea86ace46d05b --add-module=/tmp/build/lua-nginx-module-0.10.17 --add-module=/tmp/build/stream-lua-nginx-module-0.0.8 --add-module=/tmp/build/lua-upstream-nginx-module-0.07 --add-module=/tmp/build/nginx-influxdb-module-5b09391cb7b9a889687c0aa67964c06a2d933e8b --add-dynamic-module=/tmp/build/nginx-opentracing-0.9.0/opentracing --add-dynamic-module=/tmp/build/ModSecurity-nginx-b55a5778c539529ae1aa10ca49413771d52bb62e --add-dynamic-module=/tmp/build/ngx_http_geoip2_module-3.3 --add-module=/tmp/build/nginx_ajp_module-bf6cd93f2098b59260de8d494f0f4b1f11a84627 --add-module=/tmp/build/ngx_brotli
"