Fix/conntrack sysctl2 (#20)

* Inject sysctl changing nf_conntrack_max to 131072.

This addresses
#18
kubernetes-sigs/kind#2240

* Need to load nf_conntrack kmod for the sysctl setting.

* Add nf_conntrack to modules-load.d to ensure sysctl works.

This is required to be reboot safe.

Signed-off-by: Kurt Garloff <scs@garloff.de>

terraform/mgmtcluster.tf

@@ -55,6 +55,10 @@ runcmd:
   - mv /tmp/daemon.json /etc/docker/daemon.json
   - groupadd docker
   - usermod -aG docker ${var.ssh_username}
+  - echo nf_conntrack > /etc/modules-load.d/90-nf_conntrack.conf
+  - modprobe nf_conntrack
+  - echo net.netfilter.nf_conntrack_max=131072 > /etc/sysctl.d/90-conntrack_max.conf
+  - sysctl -w -p /etc/sysctl.d/90-conntrack_max.conf
   - apt -y install docker.io
 EOF