By default, the Ampere A1-based ARM64 VMs from Oracle Cloud with Ubuntu 24.04 come with some unwanted defaults for a K3s Kubernetes setup.

Changes

These were the changes made to each instance:

1. Remove iptables rules

# Apply live
sudo iptables -D FORWARD -j REJECT --reject-with icmp-host-prohibited 2>/dev/null
sudo iptables-legacy -D FORWARD -j REJECT --reject-with icmp-host-prohibited 2>/dev/null

# Persist changes
sudo vim /etc/iptables/rules.v4

# COMMENT OUT OR DELETE:
# -A INPUT -j REJECT --reject-with icmp-host-prohibited
# COMMENT OUT OR DELETE:
# -A FORWARD -j REJECT --reject-with icmp-host-prohibited

2. Increase limits via sysctl

# Apply live
sudo sysctl fs.inotify.max_user_watches=524288
sudo sysctl fs.inotify.max_user_instances=512

# Persist changes
echo "fs.inotify.max_user_watches=524288" | sudo tee -a /etc/sysctl.d/99-kubernetes.conf
echo "fs.inotify.max_user_instances=512" | sudo tee -a /etc/sysctl.d/99-kubernetes.conf
sudo sysctl --system

3. Use legacy iptables backend

update-alternatives --set iptables /usr/sbin/iptables-legacy
update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy

Additional notes

• Do NOT run Docker alongside K3s.

• Do NOT use ufw / firewalld or any other firewall.