Messing with CentOS 8 kickstart in libvirt

Today, I was learning some practical details about Dracut, Anaconda and NetworkManager. In short, the conclusion is we will stick with generating ifcfg scripts in Foreman but I just wanted to share the command which I used to quickly provision RHEL 8.0 to test generated networking configuration.

I created a kickstart script for RHEL 8 / CentOS 8 and published it over HTTP:

text
network --device=enp1s0 --activate --bootproto=dhcp --noipv6 --hostname ks-test
firewall --enabled
url --url="http://mirror.centos.org/centos/8/BaseOS/x86_64/kickstart"
rootpw --plaintext redhat
keyboard --xlayouts=us --vckeymap=us
lang en_US.UTF-8
selinux --enforcing
logging --level=info
timezone US/Eastern
reboot
bootloader --location=mbr
clearpart --all --initlabel
reqpart
part / --fstype="ext4" --size=4000
%packages
@core
%end

Make sure to replace the CentOS URL with something close to you, or even your own mirror which was my case. Then, to create a VM to play around with do:

sudo virt-install --name ks-test \
  --vcpus 2 --ram 3500 \
  --disk path=/var/lib/libvirt/images/ks-test.qcow2,format=qcow2,size=8 \
  --os-variant rhel8.0 --graphics spice,listen=0.0.0.0 --noautoconsole \
  -l http://mirror.centos.org/centos/8/BaseOS/x86_64/kickstart \
  -x ks=http://www.example.com/kickstart.ks \
  -w network=default -w network=default -w network=default -w network=default

This one has four network cards all connected to “default” libvirt NAT network. Note the www.example.com host is serving the kickstart I’ve shown above. That’s all, hope it is useful.

Now, I was messing around with various networking setups:

network --device=enp1s0 --activate --bootproto=dhcp --noipv6 --hostname ks-test
network --device=enp2s0 --nodefroute --noipv4 --ipv6 fd00:aaaa:bbbb:cc::1 --vlanid 13 --interfacename=avlan13
network --device=enp3s0 --noipv4 --noipv6
network --device=enp4s0 --noipv4 --noipv6
network --device=bond0 --nodefroute --noipv4 --ipv6 fd00:aaaa:bbbb:cc::2 --bondslaves enp3s0,enp4s0 --bondopts=mode=active-backup,balance-rr;primary=enp3s0 --vlanid 13 --interfacename=bvlan13

I have found that it’s much better to stick with generating ifcfg scripts ourselves in %post section. Although most of the limitations were solved in RHEL 7 and higher (VLAN, bond, team, bridge can be configured) some interfaces (slaves specifically) are being initialized by dracut and this would need to be workarounded. In the end, Dracut and Anaconda writes ifcfg files the same as we do, so there is no reason to do it this way. Also, ifcfg can be theoretically reused on other distibutions granted these were made for Red Hat configuration backward compatibility.

In the future, if we want to move to more consistent network generation, native NetworkManager ini files is probably way to go because nmcli command cannot be used in %post section in kickstart (NetworkManager is not running in the installed OS chroot). Alternatively, a man-in-middle could be used like Ansible or Netplan.

Until next time!