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Oct 032015
 

One thing that has always puzzled me about Linux Containers was why it is necessary to configure the network address in two places – the container configuration, and the operating system configuration. The short answer is that it isn't.

If you configure network addresses statically within the container configuration :-

» grep net /var/lib/lxc/mango/config 
# networking
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = br0
lxc.network.ipv4 = 10.0.0.35/16
lxc.network.ipv4.gateway = 10.0.0.1
lxc.network.ipv6 =         2001:0db8:ca2c:dead:0000:0000:0000:000a/64
lxc.network.ipv6.gateway = 2001:0db8:ca2c:dead:0000:0000:0000:0001

Then the configuration within the container's operating system can simply be :-

» cat /var/lib/lxc/mango/rootfs/etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual
iface eth0 inet6 manual

And that works fine.

Oct 032015
 

One of the things that has been mildly irritating me about my little collection of Linux containers has been that in addition to the statically defined IPv6 addresses, there is also an automatically defined IPv6 address :-

» lxc-ls --fancy
NAME      STATE    IPV4       IPV6                                                              AUTOSTART  
---------------------------------------------------------------------------------------------------------
apricot   RUNNING  10.0.0.34  2001:db8:ca2c:dead:21e:a0ff:feb6:6a, 2001:db8:ca2c:dead::3eb      YES        
chagers   RUNNING  10.0.0.32  2001:db8:ca2c:dead:804a:bfff:fe83:f98d, 2001:db8:ca2c:dead::5e11  YES        
glanders  RUNNING  10.0.0.31  2001:db8:ca2c:dead:21e:a0ff:feb6:66, 2001:db8:ca2c:dead::ba11     YES        
lyme      RUNNING  10.0.0.30  2001:db8:ca2c:dead:21e:a0ff:feb6:65, 2001:db8:ca2c:dead::cafe     YES        
mango     RUNNING  10.0.0.35  2001:db8:ca2c:dead:6c42:24ff:fe7d:4e9, 2001:db8:ca2c:dead::a      YES        
peach     RUNNING  10.0.0.33  2001:db8:ca2c:dead:21e:a0ff:feb6:68, 2001:db8:ca2c:dead::3a11     YES        
rhubarb   RUNNING  10.0.0.40  2001:db8:ca2c:dead:21e:a0ff:feb6:69, 2001:db8:ca2c:dead::dead     YES  

Now this is hardly the end of the world, but it is not tidy and it is the sort of thing that may lead to problems down the road if servers are communicating on an address that is not reverse DNS registered. Or indeed when someone contacts a server on an address such as 2001:db8:ca2c:dead::3eb and the reply comes from 2001:db8:ca2c:dead:21e:a0ff:feb6:6a.

After any number of false starts, the answer is quite simple – use sysctl to turn off autoconfigured address from within the container; which doesn't make much sense logically – containers don't have a kernel of their own, so the global kernel should be the one that is tuned. However :-

for container in $(lxc-ls)
do
  echo net.ipv6.conf.eth0.autoconf = 0 >> /var/lib/lxc/$container/rootfs/etc/sysctl.conf
done

Does the trick (after a reboot)  :-

» lxc-ls --fancy
NAME      STATE    IPV4       IPV6                                                              AUTOSTART  
---------------------------------------------------------------------------------------------------------
apricot   RUNNING  10.0.0.34  2001:db8:ca2c:dead:21e:a0ff:feb6:6a, 2001:db8:ca2c:dead::3eb      YES        
chagers   RUNNING  10.0.0.32  2001:db8:ca2c:dead:18d9:99ff:fe28:3591, 2001:db8:ca2c:dead::5e11  YES        
glanders  RUNNING  10.0.0.31  2001:db8:ca2c:dead:21e:a0ff:feb6:66, 2001:db8:ca2c:dead::ba11     YES        
lyme      RUNNING  10.0.0.30  2001:db8:ca2c:dead::cafe                                          YES        
mango     RUNNING  10.0.0.35  2001:db8:ca2c:dead:2411:80ff:feb9:6600, 2001:db8:ca2c:dead::a     YES        
peach     RUNNING  10.0.0.33  2001:db8:ca2c:dead::3a11                                          YES        
rhubarb   RUNNING  10.0.0.40  2001:db8:ca2c:dead::dead                                          YES        

Except for the older containers 🙁 

I've obviously missed something, but fixing nearly half of the containers is a good start.

After attending to pending upgrades (some of my old containers were still running wheezy), and setting the network configuration to manual, one of the recalictrant containers (glanders) lost it's autoconfigured address. 

Two more containers lost their unwanted extra addresses after "fixing" their configuration. I'm not sure what was wrong with the old configuration, but after copying and modifying a recently created container configuration, they rebooted with just one IPv6 address. The last one was mango, but after an extra reboot, it also was fixed :-

» lxc-ls --fancy
NAME      STATE    IPV4       IPV6                      AUTOSTART  
-----------------------------------------------------------------
apricot   RUNNING  10.0.0.34  2001:db8:ca2c:dead::3eb   YES        
chagers   RUNNING  10.0.0.32  2001:db8:ca2c:dead::5e11  YES        
glanders  RUNNING  10.0.0.31  2001:db8:ca2c:dead::ba11  YES        
lyme      RUNNING  10.0.0.30  2001:db8:ca2c:dead::cafe  YES        
mango     RUNNING  10.0.0.35  2001:db8:ca2c:dead::a     YES        
peach     RUNNING  10.0.0.33  2001:db8:ca2c:dead::3a11  YES        
rhubarb   RUNNING  10.0.0.40  2001:db8:ca2c:dead::dead  YES        
Jul 272009
 

I am a big fan of ‘self-documenting’ systems where the system has enough ‘comments’ to describe how it is configured and what things are doing. Unfortunately Solaris zones (or containers if you are so inclined to use the marketing name) lack one feature that would assist this :-

# zoneadm list -d
global
black                  Stealth Secondary DNS
grey                   Webserver for project X
white                  Mailbox server for project Y
blue                   Oracle DBMS for project X
puce                   MySQL DBMS for project X

It would seem that project Y hasn’t gotten beyond the talking stage 🙂

Yes, you’ve guessed it. Solaris zones could do with a “description” attribute to assist in documentation.

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