Boot strap : NAT Instance

This is the user data boot strap script which 'makes' your EC2 instance into a NAT instance:
#!/bin/sh

echo 1 > /proc/sys/net/ipv4/ip_forward

echo 0 > /proc/sys/net/ipv4/conf/eth0/send_redirects

/sbin/iptables -t nat -A POSTROUTING -o eth0 -s 0.0.0.0/0 -j MASQUERADE

/sbin/iptables-save > /etc/sysconfig/iptables

mkdir -p /etc/sysctl.d/

cat <<EOF > /etc/sysctl.d/nat.conf

net.ipv4.ip_forward = 1

net.ipv4.conf.eth0.send_redirects = 0

EOF