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@abeyt
Last active August 29, 2015 14:22
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#!/bin/bash
# Configure the instance to run as a Port Address Translator (PAT) to provide
# Internet connectivity to private instances.
function log { logger -t "vpc" -- $1; }
function die {
[ -n "$1" ] && log "$1"
log "Configuration of PAT failed!"
exit 1
}
# Sanitize PATH
PATH="/usr/sbin:/sbin:/usr/bin:/bin"
log "Determining the MAC address on eth0..."
ETH0_MAC=$(cat /sys/class/net/eth0/address) ||
die "Unable to determine MAC address on eth0."
log "Found MAC ${ETH0_MAC} for eth0."
VPC_CIDR_URI="http://169.254.169.254/latest/meta-data/network/interfaces/macs/${ETH0_MAC}/vpc-ipv4-cidr-block"
log "Metadata location for vpc ipv4 range: ${VPC_CIDR_URI}"
VPC_CIDR_RANGE=$(curl --retry 3 --silent --fail ${VPC_CIDR_URI})
if [ $? -ne 0 ]; then
log "Unable to retrive VPC CIDR range from meta-data, using 0.0.0.0/0 instead. PAT may masquerade traffic for Internet hosts!"
VPC_CIDR_RANGE="0.0.0.0/0"
else
log "Retrieved VPC CIDR range ${VPC_CIDR_RANGE} from meta-data."
fi
log "Enabling PAT..."
sysctl -q -w net.ipv4.ip_forward=1 net.ipv4.conf.eth0.send_redirects=0 && (
iptables -t nat -C POSTROUTING -o eth0 -s ${VPC_CIDR_RANGE} -j MASQUERADE 2> /dev/null ||
iptables -t nat -A POSTROUTING -o eth0 -s ${VPC_CIDR_RANGE} -j MASQUERADE ) ||
die
sysctl net.ipv4.ip_forward net.ipv4.conf.eth0.send_redirects | log
iptables -n -t nat -L POSTROUTING | log
log "Configuration of PAT complete."
exit 0
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