[libvirt] Making DHCP leases available to local DNS server through dnsmasq

[Michal Privoznik]

[Usually, it's not a good idea to merge threads on technical lists]

On 06/16/2017 02:38 PM, jean-christophe manciot wrote:
>>
>> libvirt-nss is not for translating DNS names, rather than libvirt guest
>> names
> 
> 
> I meant hostname/guest name. There is no static DNS in /etc/hosts for the
> VMs and no specific records in DNS server.

Well, how do you expect other hosts to translate FQDNs then?

> 
> Can you see the guest in: /var/lib/libvirt/dnsmasq/virbr0.{macs,status}
>>
> 
>  # cat /var/lib/libvirt/dnsmasq/virbr0.{macs,status}
> [
>   {
>     "domain": "KVM-Ubuntu-GNS3-Server-17.04",
>     "macs": [
>       "52:54:00:03:9f:9f"
>     ]
>   }
> ]
> [
>   {
>     "ip-address": "192.168.122.124",
>     "mac-address": "52:54:00:03:9f:9f",
>     "hostname": "KVM-Ubuntu-GNS3-Server-17",
>     "expiry-time": 1497617966
>   }
> ]

Based on this contents, you should be able to ping both
"KVM-Ubuntu-GNS3-Server-17" and "KVM-Ubuntu-GNS3-Server-17.04"

> 
> You need to restart the network after you've set up the NSS module.
> 
> 
> I've rebooted the system.
> 
> I am using something along the lines of:
> 
> 
>>  $ cat /etc/dnsmasq.d/libvirt.conf
> 
>  server=/virt/192.168.213.1
> 
>  server=/213.168.192.in-addr.arpa/192.168.213.1/
> 
> 
> I have no /etc/dnsmasq.d/libvirt.conf, but in */etc/dnsmasq.conf*:
> *local=/actionmystique.net/ <http://actionmystique.net/>*
> 
> I thought this would add that domain name to the answers from whatever is
> found in DHCP leases.
> The comment says:
> # Add local-only domains here, queries in these domains are answered
> # from /etc/hosts or DHCP only.
> Since the first libvirt-nss module ("libvirt" plugin) looks into DHCP
> server leases, the above setting should work, shouldn't it?
> 
> Actually, I've just realized that there is a discrepancy between the
> libvirt VM guest name and the Ubuntu hostname, where the trailing ".04" has
> been automatically removed.
> So, the* hostname (not guest name) is accessible*:
> # ping KVM-Ubuntu-GNS3-Server-17
> PING KVM-Ubuntu-GNS3-Server-17 (192.168.122.124) 56(84) bytes of data.
> 64 bytes from KVM-Ubuntu-GNS3-Server-17 (192.168.122.124): icmp_seq=1
> ttl=64 time=0.191 ms
> 64 bytes from KVM-Ubuntu-GNS3-Server-17 (192.168.122.124): icmp_seq=2
> ttl=64 time=0.302 ms

Yup, so the NSS module is working. Also, it's worth noting that NSS
module is meant to be single host only. I mean, it isn't a DNS server or
something. It's purely local. Although, based on the contents of the
files both names should work, with and without trailing .04;

> ...
> *but not he FQDN*:
> # ping KVM-Ubuntu-GNS3-Server-17.actionmystique.net
> ping: KVM-Ubuntu-GNS3-Server-17.actionmystique.net: Name or service not
> known

Again, if you want DNS record for this name, you need to put the record
into the DNS server. Libvirt does not do that for you.

Michal