Simple update and clone an Amazon EC2 EBS Boot image

Introduction

Well there is already an update to Chef’s Ohai library. At first I thought, “Oh no, I have to generate another EC2 image”. But then I remember reading that you can update and clone a running EBS boot image.

One of the cool features of using an Amazon EC2 instance that boots from an EBS Snapshot is that its easy to create new boot images from an existing running EC2 instance, assuming that you are running an EC2 instance that is itself bootable from an EBS Image.

Prerequisites

The following expects that you have a recent copy of the Amazon ec2-api-tools on the instance and that you have recent version of the ec2-api-tools on your host development system.

Start up an instance, make changes

Start up an instance you can use as a base, for instance the one we created in Using the Official Opscode 0.8.x Gems to build EC2 AMI Chef Client and Server

Get the name of the instance

First you will need the instance name of your instance you want to copy. You can use Elasticfox or other tool. Or run the following command on the instance:

wget -qO- http://instance-data/latest/meta-data/instance-id

On another host

The rest of the instructions will be run on your host development system (not the system you are copying). This makes it so you don’t have to put your Amazon Certs onto the machine you are cloning (you don’t want those keys to end up on the cloned image)

Create some shell defines

To make the instructions easier make some defines we’ll use in commands. Tune them for your environment.

# This will be the instance id of the running instance you want to clone
instanceid=i-07202042

# Some info for creating the name and description
codename=karmic
release=9.10
tag=server
region=us-west-1
availability_zone=us-west-1a

# Make sure you set this as appropriate
# 64bit
arch=x86_64
arch2=amd64
#32bit
arch=i386
arch2=i386
now=$(date +%Y%m%d-%H%M)

# Make this specific to what you are making
prefix=runa-chef-0.8.4-ubuntu-$release-$codename-$tag-$arch-$now
description="Runa Chef 0.8.4 Ubuntu $release $codename $tag $arch $now"

Get the info about your running instance

Use Elasticfox or your favorite tool or the following command to get the volume id of the instance

ec2-describe-instances --region $region "$instanceid" > /tmp/instance_info
volumeid=$(egrep ^BLOCKDEVICE /tmp/instance_info | cut -f3); echo $volumeid
kernel=$(egrep ^INSTANCE /tmp/instance_info | cut -f13); echo $kernel
ramdisk=$(egrep ^INSTANCE /tmp/instance_info | cut -f14) ;echo $ramdisk

Shutdown  the instance

Its not clear if you really need to do this. But when I first tried doing it without shuting down the instance, the snapshots took forever.

Create a new snapshot

snapshotid=$(ec2-create-snapshot -region $region -d "$description" $volumeid | cut -f2)

Register the new image

ec2reg --region $region -s $snapshotid -a $arch --kernel $kernel --ramdisk $ramdisk -d "$description" -n "$prefix"

The result of this command will be the ami image name. After this completes, the image and snapshot can be used to create new instances.