Elastic IP on Boot - Not too Much of a Stretch

It is quite usual to have a EC2 instance with a tied Elastic IP you need to reboot/stop from time to time. Unfortunately for you every time you do so, the elastic IP association is lost, forcing you to manually reattaching it again.

There is however a very easy way to solve this problem, by just using a script at boot. Just like a normal Unix service.

/etc/ec2autoeip.conf (Config file sample)

AWS_ACCESS_KEY = 'xxxxxxxxxxxxxxxxxx' AWS_SECRET_ACCESS_KEY = 'yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy’' IP = 'ww.xx.yy.zz'

/etc/init.d/ec2autoeip (The actual service script code)

#!/usr/bin/python import sys import urllib import boto.ec2 execfile("/etc/ec2autoeip.conf") instance_id = urllib.urlopen("http://169.254.169.254/latest/meta-data/instance-id").read() zone = urllib.urlopen("http://169.254.169.254/latest/meta-data/placement/availability-zone").read()[:-1] conn = boto.ec2.connect_to_region(zone, aws_access_key_id = AWS_ACCESS_KEY, aws_secret_access_key = AWS_SECRET_ACCESS_KEY, is_secure = False) if len(sys.argv) > 1 and sys.argv[1]=="start": conn.associate_address(instance_id,IP) print("Attaching " + IP + " to " + instance_id) elif len(sys.argv) > 1 and sys.argv[1]=="stop": conn.disassociate_address(IP) print("Deattaching " + IP)

Finally is time to register the service to run at boot, in Debian and Ubuntu you can do it like that:

root@somewhere# update-rc.d ec2autoeip defaults

This script uses the awesome boto python library so you will need to install it in order for the script to work properly.


Emilio Garcia
Cloudreach Senior Engineer