[nodesocket]

I recently just created a NAT instance AMI (using Packer) for use on AWS based on Debian 12. The official AWS NAT instance AMI is horrendously outdated and based on end-of-life AWS Linux v1. At any rate, I was surprised to find it's incredibly easy to do using iptables. It's essentially just the following four iptables rules.

    sudo iptables -t nat -A POSTROUTING -o ens5 -j MASQUERADE
    sudo iptables -F FORWARD
    sudo iptables -A FORWARD -i ens5 -m state --state RELATED,ESTABLISHED -j ACCEPT
    sudo iptables -A FORWARD -o ens5 -j ACCEPT

    sudo iptables-save | sudo tee /etc/iptables/rules.v4 > /dev/null

Lastly a small change in sysctl to enable ipv4 forwarding:

    cat <<'EOF' | sudo tee /etc/sysctl.d/99-ip-forwarding.conf > /dev/null
    net.ipv4.ip_forward=1
    EOF

    sudo sysctl --system