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

[jean-christophe manciot]

Yes, except that it *does not work*. As you can see below, libnss-libvirt
is installed and configured, but the VM "KVM-Ubuntu-GNS3-Server-17.04" is
not reachable through its DNS name.

# apt-cache policy libnss-libvirt
libnss-libvirt:
  Installed: 3.0.0-4
...
# cat /etc/nsswitch.conf
passwd:         compat
group:          compat
shadow:         compat

hosts: files libvirt libvirt_guest mdns4_minimal [NOTFOUND=return] resolve
[!UNAVAIL=return] dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

# systemctl status libvirtd
● libvirtd.service - Virtualization daemon
   Loaded: loaded (/lib/systemd/system/libvirtd.service; enabled; vendor
preset: enabled)
   Active: active (running) since Fri 2017-06-16 11:44:59 CEST; 11min ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 9448 (libvirtd)
      CPU: 1.790s
   CGroup: /system.slice/libvirtd.service
           ├─ 5556 /usr/sbin/dnsmasq
--conf-file=/var/lib/libvirt/dnsmasq/virtual-mgt-5.conf --leasefile-ro
--dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
           ├─ 5557 /usr/sbin/dnsmasq
--conf-file=/var/lib/libvirt/dnsmasq/virtual-mgt-5.conf --leasefile-ro
--dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
 ...
           ├─ 8805 /usr/sbin/dnsmasq
--conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro
--dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
           ├─ 8806 /usr/sbin/dnsmasq
--conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro
--dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper
           ├─ 9448 /usr/sbin/libvirtd
           └─15116 qemu-system-x86_64 -enable-kvm -name
guest=KVM-Ubuntu-GNS3-Server-17.04,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/

...
Jun 16 11:55:14 samsung-ubuntu dnsmasq-dhcp[8805]: DHCPREQUEST(virbr0)
192.168.122.124 52:54:00:03:9f:9f
Jun 16 11:55:14 samsung-ubuntu dnsmasq-dhcp[8805]: DHCPACK(virbr0)
192.168.122.124 52:54:00:03:9f:9f KVM-Ubuntu-GNS3-Server-17
# ping KVM-Ubuntu-GNS3-Server-17.04
ping: KVM-Ubuntu-GNS3-Server-17.04: Name or service not known
# ping KVM-Ubuntu-GNS3-Server-17.04.actionmystique.net
ping: KVM-Ubuntu-GNS3-Server-17.04.actionmystique.net: Name or service not
known
# ping 192.168.122.124
PING 192.168.122.124 (192.168.122.124) 56(84) bytes of data.
64 bytes from 192.168.122.124: icmp_seq=1 ttl=64 time=0.181 ms
64 bytes from 192.168.122.124: icmp_seq=2 ttl=64 time=0.165 ms

A few possible explanations for that issue are:
- something is not configured correctly
- there is an incompatibility with NetworkManager
- there is a bug with libnss-libvirt
- I'm missing something

On Fri, Jun 16, 2017 at 10:49 AM, Michal Privoznik <mprivozn at redhat.com>
wrote:

> 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
>



-- 
Jean-Christophe
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