Autogenerate host information on ec2 on instance startup. Run from /etc/rc.local

ec2-set-host-info

#!/bin/bash
#
# Save somewhere and chmod o+x it and Run it from /etc/rc.local
# Modify and re-arrange as you see fit
#

# Change as appropriate
DOMAIN=local
 
USER_DATA=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/hostname`
HOSTNAME=`echo $USER_DATA`
LOCAL_IPV4=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/local-ipv4`
USER_DATA=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/public-hostname`
PUBLIC_HOSTNAME=`echo $USER_DATA`
IPV4=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/public-ipv4`

# setup
hostname $HOSTNAME
echo $HOSTNAME > /etc/hostname
 
# FQDN
cat<<EOF > /etc/hosts
# Autogenerated host information
127.0.0.1 localhost
$LOCAL_IPV4 $PUBLIC_HOSTNAME $HOSTNAME.$DOMAIN $HOSTNAME
# $IPV4 $PUBLIC_HOSTNAME # reference
 
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
EOF