When working with Amazon EC2 instances, you’ve probably experienced the need to change the default hostname to something more meaningful than “ip-10-205-14-33”. While simply issuing a hostname command will do the trick, it requires login into the machine. If you also need to properly define the fqdn (fully qualified domain name) of the machine, it requires a modification of the /etc/hosts file as well or more if you’ve setup a DNS server.
Setting the desired hostname and fqdn for the instance can be critical if you’re automating deployment with Chef and expect to retrieve those values later on. A simple approach is to pass user data when creating the instance and use a script to read it and populate the hostname.
Thanks to Ternery labs for this awesome script. I’ve updated it to reflect the recent October 2012 changes to the hostname URL.
We’re going to start by creating a script
Copy and paste the information below into your script.
# Replace this with your domain
USER_DATA=`/usr/bin/curl -s http://169.254.169.254/latest/user-data`
IPV4=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/public-ipv4`
# Set the host name
echo $HOSTNAME > /etc/hostname
# Add fqdn to hosts file
# This file is automatically genreated by ec2-hostname script
$IPV4 $HOSTNAME.$DOMAIN $HOSTNAME
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
Now Save and exit your editor.
Next, we need to mark the script as executable
$ chmod o+x ec2-hostanme.sh
Finally, add the following line to so that it runs every time the instance restarts
You can take this script one step further and save your instance as a new AMI, so that whenever you start a new image, the script will already be in place for you.