id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2212	Returns HTTP status code 502 Bad Gateway when proxy is down (proxy_pass)	chealer@…		"The following occurs with an old version. Apologies if it's already been fixed.

Ever since I started dealing with nginx and PHP-FPM, I've often seen a rare HTTP error, 502 Bad Gateway: https://datatracker.ietf.org/doc/html/rfc7231#section-6.6.3

I figured out that must be simply because it occurs in a very common case: when the upstream is simply down. If for example I have the following:

{{{
    location / {
        proxy_pass http://localhost:8080;
    }
}}}

...then if the server supposed to listen on 8080 is down, nginx will fail to connect:

{{{
2021/06/25 12:16:00 [error] 979#979: *320225 connect() failed (111: Connection refused) while connecting to upstream, client: 10.102.0.230, server: [..., request: ""GET /nuxeo/authentication/token?[...] HTTP/1.1"", upstream: ""http://127.0.0.1:8080/nuxeo/authentication/token?applicationName=[...]"", host: ""serveurnuxeo""
}}}

...and reply with a 502 error:

{{{
10.102.0.230 - tspod211 [25/Jun/2021:11:20:45 -0400] ""GET /nuxeo/authentication/token?applicationName=[...] HTTP/1.1"" 502 166 ""-"" ""GuzzleHttp/6.2.1 curl/7.58.0 PHP/7.2.24-0ubuntu0.18.04.7""
}}}

I do not see any status code specifically designed for offline proxies, but I suppose a 503 code or a custom code should be used instead."	defect	closed	minor		nginx-core	1.14.x	wontfix			Linux spssoal13a 4.15.0-144-generic #148-Ubuntu SMP Sat May 8 02:33:43 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.14.0 (Ubuntu)
built with OpenSSL 1.1.1  11 Sep 2018
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -fdebug-prefix-map=/build/nginx-H4cN7P/nginx-1.14.0=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Wdate-time -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fPIC' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --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 --modules-path=/usr/lib/nginx/modules --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-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_v2_module --with-http_dav_module --with-http_slice_module --with-threads --with-http_addition_module --with-http_geoip_module=dynamic --with-http_gunzip_module --with-http_gzip_static_module --with-http_image_filter_module=dynamic --with-http_sub_module --with-http_xslt_module=dynamic --with-stream=dynamic --with-stream_ssl_module --with-mail=dynamic --with-mail_ssl_module"