[lxc-users] How to resolve the *.lxd hostnames from LXD (i.e. outside of the containers)

[Ivan Ogai]

Hi Simos,

your email has been useful, thanks!

What I do is to put in /etc/resolvconf/resolv.conf.d/head what I want
to be at the top of /etc/resolv.conf after each reboot.

To add the change immediately:

sudo resolvconf -u

Ivan

* Simos Xenitellis <simos.lists at googlemail.com> [2016-08-29 15:13]:
> Hi All,
> 
> If you are in a container, you can access the other containers through
> their *.lxd hostnames.
> For example, you can
> 
> root at c1:~# ping c2.lxd
> PING c2.lxd (10.60.113.13) 56(84) bytes of data.
> 64 bytes from oag.lxd (10.60.113.13): icmp_seq=1 ttl=64 time=0.064 ms
> 
> 
> However, if you are outside of the containers, by default you can't
> 
> ubuntu at desktop:~$ ping c1.lxd
> ping: unknown host c1.lxd
> ubuntu at desktop:~$
> 
> 
> The source of the problem is that LXD uses a separate instance of
> "dnsmasq" in order to serve those *.lxd domains.
> 
> If you are trying out LXD on a Ubuntu Desktop (i.e. NetworkManager is
> running), then the solution is to add a configuration file as follows:
> 
> ubuntu at desktop:~$ cat /etc/NetworkManager/dnsmasq.d/lxd
> server=/lxd/10.60.113.1
> server=/113.60.10.in-addr.arpa/10.60.113.1
> ubuntu at desktop:~$
> 
> The first line says that for domains of the form *.lxd, use the
> specific DNS server (10.60.113.1 in this case). The second line deals
> with reverse queries.
> Then, restart the network with
> ubuntu at desktop:~$ sudo systemctl restart NetworkManager
> 
> By doing so, the following will now work,
> 
> ubuntu at desktop:~$ host c1.lxd
> c1.lxd has address 10.60.113.13
> ubuntu at desktop:~$ host 10.60.113.13
> 13.113.60.10.in-addr.arpa domain name pointer c1.lxd.
> 
> 
> However, on an Ubuntu server, NetworkManager (dnsmasq specifically) is
> not installed by default.
> DHCP grabs the DNS configuration and adds it to /etc/resolv.conf
> In this case, we need to prepend the following two lines to /etc/resolv.conf
> 
> root at lxdserver:~# cat /etc/resolv.conf
> search lxd
> nameserver 10.60.113.1
> 
> ... rest of configuration...
> 
> root at lxdserver:~#
> 
> The "search lxd" line will allow us to type
> ubuntu at lxdserver:~# host c1
> c1 has address 10.60.113.13
> (i.e., no need to specify the .lxd suffix).
> 
> The issue is, how to get /etc/resolv.conf to be autocreated like that?
> Like that (file: /etc/dhcp/dhclient.conf),
> 
> diff --git a/dhcp/dhclient.conf b/dhcp/dhclient.conf
> index 1e4ec62..73a6210 100644
> --- a/dhcp/dhclient.conf
> +++ b/dhcp/dhclient.conf
> @@ -21,8 +21,8 @@ request subnet-mask, broadcast-address, time-offset, routers,
> 
>  #send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
>  #send dhcp-lease-time 3600;
> -#supersede domain-name "fugue.com home.vix.com";
> -#prepend domain-name-servers 127.0.0.1;
> +supersede domain-name "lxd";
> +prepend domain-name-servers 10.54.220.1;
>  #require subnet-mask, domain-name-servers;
>  timeout 300;
>  #retry 60;
> 
> You need to be careful when you run again dhclient ("sudo dhclient -r
> ; dhclient") on a VPS over SSH as you may lose connectivity; have a
> console window open when trying this.
> 
> According to http://linux.die.net/man/5/resolv.conf
> the first nameserver line in /etc/resolv.conf takes precedent and the
> subsequent lines are used only if the previous fail.
> 
> My worry here is whether it is good to expose the dnsmasq of LXD for
> all DNS queries, on an Ubuntu server.
> I am considering between
> a. have the LXD dnsmasq do the DNS queries as primary nameserver
> b. set up dnsmasq on the server for caching DNS queries, then use the
> first trick (server=/.../nameserver) to direct the queries to the
> correct nameserver.
> 
> Hope all these have been useful to some. Any feedback is welcome.
> 
> Simos