id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
896	Maxed out DNS connections	alex.squarevault.com@…		"nginx seems to be establishing and maintaining as many DNS connections as it can.

In my nginx.conf file I have the following lines:

  
{{{
resolver 10.0.80.11 10.0.80.12 8.8.8.8 8.8.4.4 valid=300s;
  resolver_timeout 5s;
}}}



Here is a command that lets you see how many connection to an IP your server currently has open that are ""ESTABLISHED"".

{{{
watch -n 0 ""netstat -ntu | grep 'ESTABLISHED' | awk '{print \$5}' | cut -d: -f1 | sort | uniq -c | sort -n -r""
}}}

When I run this command I get the following results:

[[Image(http://i.imgur.com/c7Q2RKi.png)]]

As you can see, there are 80 connection to all of my defined namespace resolvers. That number never goes any higher. 
On my fresh restart of the nginx process, the first resolver IP will slowly increase in connections until it hits 80, and then the next will slowly increase in connections until it hits 80 and then the third and then the fourth. 
It should probably be noted that my machine has 80 cores. Since that's the only other logical thing with the number 80 on my box, I have to assume that it's related. 

I do not know if this is causing a performance issue. I would assume the reason that it's establishing new connections is because the previous ones are unavailable, so this may be a bottleneck for my applications."	defect	closed	major		nginx-core	1.8.x	invalid	DNS connections established		Linux server1 3.5.0-51-generic #77~precise1-Ubuntu SMP Thu Jun 5 00:48:28 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.8.0
built with OpenSSL 1.0.1 14 Mar 2012 (running with OpenSSL 1.0.1f 6 Jan 2014)
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -fPIE -fstack-protector --param=ssp-buffer-size=4 -Wformat -Wformat-security -Werror=format-security -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro -Wl,-z,now' --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 --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-ipv6 --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_gzip_static_module --without-http_browser_module --without-http_geo_module --without-http_limit_req_module --without-http_limit_zone_module --without-http_memcached_module --without-http_referer_module --without-http_scgi_module --without-http_split_clients_module --without-http_ssi_module --without-http_userid_module --without-http_uwsgi_module --add-module=/build/buildd/nginx-1.8.0/debian/modules/nginx-echo
"