install | setup | simple | routing states | check-ha
tested on slackware current (oct 2021) and debian12
apt install nftables keepalived
    slackpkg install sysvinit-functions
    ls -lF /etc/rc.d/init.d/functions
    ls -lF /sbin/consoletype
    slackpkg install iptables libnftnl libpcap dbus-1
    slackpkg install nftables jansson
    sbopkg -i keepalived
    cat /etc/default/keepalived # no change required
we need a dedicated user for the check and notify scripts to run
    grep ^keepalive /etc/group
    grep ^keepalive /etc/passwd
    groupadd --system keepalive
    useradd --system -s /bin/bash -g keepalive -d /var/tmp --no-create-home keepalive
    # -s /sbin/nologin
(seen with the debian build)
-g requires configure option --enable-log-file
==> enable at build time or be happy with syslog
https://slackbuilds.org/repository/15.0/network/keepalived/
https://serverfault.com/questions/1115426/keepalived-with-log-file-doesnt-work ==> enable at build time