Created
December 29, 2023 12:16
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AWS Nat Instance EC2 Port Address Translator
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#!/bin/bash | |
# Configure the instance to run as a Port Address Translator (PAT) to provide | |
# Internet connectivity to private instances. | |
# https://docs.aws.amazon.com/vpc/latest/userguide/VPC_NAT_Instance.html | |
set -x | |
echo "Determining the MAC address on eth0" | |
ETH0_MAC=`/sbin/ifconfig | /bin/grep eth0 | awk '{print tolower($5)}' | grep '^[0-9a-f]\{2\}\(:[0-9a-f]\{2\}\)\{5\}$'` | |
if [ $? -ne 0 ] ; then | |
echo "Unable to determine MAC address on eth0" | logger -t "ec2" | |
exit 1 | |
fi | |
echo "Found MAC: ${ETH0_MAC} on eth0" | logger -t "ec2" | |
VPC_CIDR_URI="http://169.254.169.254/latest/meta-data/network/interfaces/macs/${ETH0_MAC}/vpc-ipv4-cidr-block" | |
echo "Metadata location for vpc ipv4 range: ${VPC_CIDR_URI}" | logger -t "ec2" | |
VPC_CIDR_RANGE=`curl --retry 3 --retry-delay 0 --silent --fail ${VPC_CIDR_URI}` | |
if [ $? -ne 0 ] ; then | |
echo "Unable to retrive VPC CIDR range from meta-data. Using 0.0.0.0/0 instead. PAT may not function correctly" | logger -t "ec2" | |
VPC_CIDR_RANGE="0.0.0.0/0" | |
else | |
echo "Retrived the VPC CIDR range: ${VPC_CIDR_RANGE} from meta-data" |logger -t "ec2" | |
fi | |
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 ${VPC_CIDR_RANGE} -j MASQUERADE | |
if [ $? -ne 0 ] ; then | |
echo "Configuration of PAT failed" | logger -t "ec2" | |
exit 0 | |
fi | |
echo "Configuration of PAT complete" |logger -t "ec2" | |
exit 0 |
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