Comment # 27 on bug 1171770 from Richard Brown

The problem, as we understand it right now, is that the sysctl.d settings from
/usr/lib/sysctl.d/90-kubeadm.conf are not getting correctly applied/honoured by
the kernel.

/proc seems to suggest they are applied, but obviously they don't behave that
way and IP forwarding (which is really needed for us) is not working.

Various methods of toggling/reapplying settings can get things to work (eg. the
WORKAROUND, echo 0 > /proc/sys/net/ipv4/ip_forward && echo 1 >
/proc/sys/net/ipv4/ip_forward, sysctl -a --system and such)

Quite what is going on in the kernel is still a mystery and other folk are
looking at it as I'll be going on vacation.

Meanwhile though, I have patches going to both kubernetes1.17 and 1.18 which
will run sysctl -a --system before starting kubelet, just to be sure everything
is running as configured :)

Once this patch is out there the workaround of deleting other influencing
sysctl.d config files will be redundant.