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

[Michal Privoznik]

On 06/10/2017 08:53 PM, jean-christophe manciot wrote:
> Hello everyone,
> 
> I have multiple virtual networks defined on my Server:
> # virsh net-list --all
>  Name                 State      Autostart     Persistent
> ----------------------------------------------------------
>  default              active     yes           yes
> ...
>  virtual-mgt-5        active     yes           yes
>  ...
> 
> When a VM is started on one of them with an interface which needs the
> dnsmasq DHCP server to get its IP address/len, it remains inaccessible with
> the FQDN once the IP information is acquired.
> 
> The default values are used for each dnsmasq instance:
> ● libvirtd.service - Virtualization daemon
>    Loaded: loaded (/lib/systemd/system/libvirtd.service; enabled; vendor
> preset: enabled)
>    Active: active (running) since Sat 2017-06-10 19:48:58 CEST; 3ms ago
>      Docs: man:libvirtd(8)
>            http://libvirt.org
>  Main PID: 25365 (libvirtd)
>     Tasks: 35 (limit: 4915)
>    Memory: 27.1M
>       CPU: 28ms
>    CGroup: /system.slice/libvirtd.service
>            ├─22262 /usr/sbin/dnsmasq
> --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro
> --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
>            ├─22263 /usr/sbin/dnsmasq
> --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro
> --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
> ...
>            ├─24061 /usr/sbin/dnsmasq
> --conf-file=/var/lib/libvirt/dnsmasq/virtual-mgt-5.conf --leasefile-ro
> --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
>            ├─24062 /usr/sbin/dnsmasq
> --conf-file=/var/lib/libvirt/dnsmasq/virtual-mgt-5.conf --leasefile-ro
> --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
> ...
>            ├─25365 /usr/sbin/libvirtd
>            └─25384 /usr/sbin/dnsmasq --help
> 
> I wonder whether the option "--leasefile-ro" gets in the way or not: there
> must be a key=value in /etc/libvirt/qemu/networks/<virtual_network>.xml to
> enable this behavior, but could not find it in the Network XML format
> <https://libvirt.org/formatnetwork.html>.

The --leasefile-ro argument is added unconditionally, just like
--dhcp-script. If you want to do name translation, either have static IP
addresses and edit the hosts file, or use NSS module:

https://libvirt.org/nss.html

Michal