[lxc-users] /etc/resolv.conf occasionally does not get written in LXC container with static conf

[David Favor]

Marat Khalili wrote:
> Occasionally after reboot of the host the /etc/resolv.conf file in some 
> container comes up containing only two comment lines (taken from 
> /etc/resolvconf/resolv.conf.d/head). It should be filled in accordance 
> with dns-nameservers line in /etc/network/interfaces (network 
> configuration is all static), but it doesn't, though IP address is 
> assigned correctly. Any of the following fixes the problem:
> * /etc/init.d/resolvconf reload
> * ifdown/ifup
> * lxc-stop/lxc-start
> * lxc-attach shutdown -r now
> 
> What's bizzare is there're many containers with similar configuration on 
> this host (actually, most created with the same script), but they 
> usually come up ok, and there's nothing particularly different in 
> successful and unsuccessful syslogs until some service inside (e.g. 
> Apache) realizes it's got no DNS.
> 
> Since it is hard to reproduce the problem without rebooting production 
> server, I don't even know where to dig. Probably someone has seen this 
> kind of behaviour before?
> 
> It's Ubuntu 16.04 on both host and container:
> Linux host 4.4.0-79-generic #100-Ubuntu SMP Wed May 17 19:58:14 UTC 2017 
> x86_64 x86_64 x86_64 GNU/Linux

There seems to be some ugliness with regeneration of /etc/resolv.conf at boot time.

I've seen some glitches around this process also.

In my case, I run a local copy of dnsmasq + completely disable all the
systemd-resolved lunacy, so here's how I deal with this...

Which might be more brute force than what your after + works well.

1) Completely destroy systemd-resolved

systemctl stop systemd-resolved
systemctl disable systemd-resolved
apt-get purge libnss-resolve

2) Create /etc/dnsmasq-caching.conf

port=53
listen-address=127.0.0.1
listen-address=127.0.0.53

interface=lo
bind-interfaces

no-resolv
no-hosts

# Google
server=8.8.8.8
server=8.8.4.4

3) Add to /etc/rc.local

echo "starting" | logger --tag "rc-local: dnsmasq"
dnsmasq -C /etc/dnsmasq-caching.conf

4) Create /etc/resolv.conf.override

nameserver 127.0.0.1

5) apt-get install incron

6) echo root > /etc/incron.allow

7) incrontab -e

/run/resolvconf/resolv.conf IN_CLOSE_WRITE,IN_NO_LOOP /bin/cp -f /etc/resolv.conf.override /run/resolvconf/resolv.conf
/etc/resolv.conf.override IN_CLOSE_WRITE,IN_NO_LOOP /bin/cp -f /etc/resolv.conf.override /run/resolvconf/resolv.conf

At this point the highly broken systemd-resolved is completely off.

Anytime /run/resolvconf/resolv.conf (resolvconf -u for example) or /etc/resolv.conf.override changes
/run/resolvconf/resolv.conf is overwritten using your /etc/resolv.conf.override file, so you always
know exactly what's in your resolv.conf file.

Like I said, might be overkill + ensures you know exactly how your resolution is occurring.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linuxcontainers.org/pipermail/lxc-users/attachments/20170624/4c25652f/attachment.html>