In the end I decided to skip the ubuntu ec2 scripts and do something similar. I looked into using Amazon's Route53 service as the nameservice and it was really easy to get it up and running.
Using Route53
Here is what I did; Firstly I used the IAM tools to create a user 'route53' with liberal policy permissions for interacting with the Route53 service
Create the dns group & user
iam-groupcreate -g route53 -v
iam-usercreate -u route53 -g route53
Create keys for the user and note these for later
iam-useraddkey -u route53
Give access to the group to add zones and dns records
iam-grouplistpolicies -g route53
iam-groupaddpolicy -p hostedzone -e Allow -g route53 -a route53:* -r '*'
listing the users and policies for a group
iam-grouplistusers -g route53
iam-grouplistpolicies -g route53
iam-grouplistpolicies -g route53 -p hostedzone
To add and remove dns record entries I uses the excellent python wrapper library for Route53, cli53. This takes a lot of the pain out of using route53. You can grab it from here
https://github.com/barnybug/cli53
In my case the python script is symlinked in /usr/bin as cli53. You'll need to set the following environment variables containing keys created earlier for the route53 user.
export AWS_SECRET_ACCESS_KEY=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
export AWS_ACCESS_KEY_ID=XXXXXXXXXXXXXXXXXXXXX
You need to then create a zone entry for your domain e.g. simple.org
cli53.py create simple.org
This should return you an amazon nameserver address that you can associate with your domain name via your domain name registrar, so that hostname lookups for the domain will be redirected to the Route53 servers.
Once the zone is setup, adding and removing entries to it is simple e.g.
cli53 rrcreate simple.org hostname CNAME ec2-184-73-137-40.compute-1.amazonaws.com
cli53 rrdelete simple.org hostname
We use a CNAME entry with the Public DNS name of the ec2 instance as this hostname will resolve to the public IP externally and the private IP from within EC2. The following adds an entry for a host 'test2.simple.org'.
cli53 rrcreate simple.org test2 CNAME ec2-184-73-137-40.compute-1.amazonaws.com --ttl 60 --replace
Automatically set hostname and update Route53
Now what remains is to setup a script to automatically do this when the machine boots. This solution and the following script owes huge debt to Marius Ducea's excellent tutorial found here
http://www.ducea.com/2009/06/01/howto-update-dns-hostnames-automatically-for-your-amazon-ec2-instances/
It's basically doing the same as Marius' setup, but using Route53 instead of Bind.
The script uses the simple REST based services available to each EC2 Instance at
http://169.254.169.254
to retrieve the actual Public DNS name and grab the desired hostname from the instance. The hostname is passed to the instance using the customizable 'user-data' which we can specify when we start the instance. The script expects user-data in the format
hostname=test2
The script will
- grab hostname info from the instance user-data
- grab the public DNS name from the instance metadata
- parse out the hostname
- set the hostname to the fully qualified name e.g. test2.simple.org,
- Add a CNAME record for this FQDN in Route53 point to the Public DNS Name
- write an entry into the Messages of the day so that users can see the domain to ec2 mapping when they log in
Copy and save the following as /usr/bin/autohostname.sh
#!/bin/bash
DOMAIN=simple.org
USER_DATA=`/usr/bin/curl -s http://169.254.169.254/latest/user-data`
EC2_PUBLIC=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/public-hostname`
HOSTNAME=`echo $USER_DATA| cut -d = -f 2`
#set also the hostname to the running instance
FQDN=$HOSTNAME.$DOMAIN
hostname $FQDN
export AWS_SECRET_ACCESS_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
export AWS_ACCESS_KEY_ID=xxxxxxxxxxxxxxxxxxxxxxx
# Update Route53 with a CNAME record pointing the hostname to the EC2 public DNS name
# in this way it will resolve correctly to the private ip internally to ec2 and
# the public ip externally
RESULT=`/root/dns/cli53/cli53.py rrcreate $DOMAIN $HOSTNAME CNAME $EC2_PUBLIC --ttl 60 --replace`
logger "Created Route53 record with the result $RESULT"
# write an MOTD file so that the hostname is displayed on login
MESSAGE="Instance has been registered with the Route53 nameservers as '$FQDN' pointing to ec2 domain name '$EC2_PUBLIC'"
logger $MESSAGE
cat<<EOF > /etc/update-motd.d/40-autohostname
#!/bin/bash
# auto generated on boot by /root/bin/auto_hostname.sh via rc.local
echo "$MESSAGE"
EOF
chmod +x /etc/update-motd.d/40-autohostname
exit 0
To get the script to run at boot time, we add a line in /etc/rc.local e.g.
/usr/bin/autohostname.sh
Change the user-data for the test instance to 'hostname=test2' and reboot the instance. Once it reboots, you should be able to login to it via test2.simple.org. It may take a couple of minutes for this to resolve correctly, depending on the TTLs you specified. When you login, you should see a MOTD message telling you
Instance has been registered with the Route53 nameservers as 'test2.simple.org' pointing to ec2 domain name 'ec2-184-73-137-40.compute-1.amazonaws.com'
Once you have this working with the test instance it would make sense to back it up as an AMI that you can use to create other instances with the same autohostnaming abilities.
HTH
