Systemd's networkd will drop IP-Addresses configured by other processes like Keepalived's VRRP, when it is restarted. This may happen on updates.
To prevent this following settings are required in /run/systemd/network/10-netplan-eth0.network
v242 or earlier (even if you do not use DHCP client in networkd)
[DHCP]
CriticalConnection=yes
v243 or newer
[Network]
KeepConfiguration=yes
If there is netplan in place these files will be generated.
Add critical: yes to /etc/netplan/50-cloud-init.yaml
eth1:
addresses:
- 192.0.2.67/24
gateway4: 192.0.2.1
nameservers:
addresses:
- 198.51.100.42
- 198.51.100.53
search:
- example.lcal
critical: yes
run netplan generate
This will add the CriticalConnection to your networkd configuration.
- This is the Upstream issue Show archive.org snapshot
- The Ubuntu Launchpad issue Show archive.org snapshot
Caveat for systemd 251–256
In systemd versions 251 through 256, KeepConfiguration=yes may still remove IP addresses configured by other processes, such as Keepalived VRRP addresses, during a networkd restart.
Netplan's critical: yes generates KeepConfiguration=true.
In these systemd versions, link_drop_foreign_addresses() only explicitly preserves foreign addresses for KeepConfiguration=dhcp or KeepConfiguration=static. This was reworked in systemd v257.
As a workaround for static addresses such as VRRP VIPs, add a networkd drop-in:
# /etc/systemd/network/10-netplan-eth0.network.d/keep-configuration.conf
[Network]
KeepConfiguration=static
