Using netplan this is the way to go /etc/netpan/01-netcfg.yaml

Remember to change device name and IP addresses.

For pve1.noerit.gl:

network:
    ethernets:
        eth0:
            addresses:
            #- 149.202.151.151/32
            #- 5.196.241.149/32
            - 2001:41d0:8:228::241:149/64
            dhcp4: false
            dhcp6: false
            gateway4: 188.165.199.254
            gateway6: 2001:41d0:8:22ff:ff:ff:ff:ff
            nameservers:
                addresses:
                - 213.186.33.99
                - 2001:41d0:3:163::1
                search: [noerit.gl]
            routes:
              - to: 0.0.0.0/0
                via: 176.31.241.254
                on-link: true
            routes:
              - to: ::/0
                via: 2001:41d0:8:22ff:ff:ff:ff:ff
                on-link: true
    version: 2

For pve4.hosting.gl:

network:
    ethernets:
        ens18:
            addresses:
            - 149.202.151.151/32
            - 2001:41d0:2:902c::151:151/64
            dhcp4: false
            dhcp6: false
            gateway4: 188.165.199.254
            gateway6: 2001:41d0:2:90ff:ff:ff:ff:ff
            nameservers:
                addresses:
                - 213.186.33.99
                - 2001:41d0:3:163::1
                search: [noerit.gl]
            routes:
              - to: 0.0.0.0/0
                via: 188.165.199.254
                on-link: true
            routes:
              - to: ::/0
                via: 2001:41d0:2:90ff:ff:ff:ff:ff
                on-link: true
    version: 2

Remember to delete other files in this directory if they conflict with the new file

We are using static addresses in this setup, so we need to disable IPv6 RA. Create a file /etc/sysctl.d/15-ipv6-ra.conf with the following content

net.ipv6.conf.default.autoconf=0
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.all.autoconf=0

Change /etc/cloud/cloud.cfg

preserve_hostname: true

Enable en_DK.UTF-8 UTF-8 in /etc/locale.gen

Run locale-gen

Update /etc/apt/sources.list

deb http://ubuntu.mirrors.ovh.net/ubuntu bionic main universe
deb http://ubuntu.mirrors.ovh.net/ubuntu bionic-updates main universe

deb http://security.ubuntu.com/ubuntu bionic-security main universe

Install packages

apt update
apt install mosh vim mc check-mk-agent xinetd fail2ban rdiff-backup

Update settings in /etc/xinetd.d/check_mk

flags          = IPv6
only_from      = 127.0.0.1 149.202.151.145 2001:41d0:8:228::151:145
disable        = no

Restart xinetd service

service xinetd restart

Create /etc/fail2ban/jail.d/noerit.conf and set good defaults

[DEFAULT]
bantime  = 60m
findtime  = 10m
maxretry = 4