While we have been booting from EBS a month after it came out using pivot_root - most of our implementations are based on a couple of AMIs and many different EBS snapshots and volumes. We were nonetheless happy to see Amazon's announcement to allow AMIs to boot from AMIs, it makes some of our scripts much simpler. I put this article together to show migrating an existing Linux AMI to EBS can be a trivial task.

Once you have the AMI you want to migrate booted up, ssh into the machine. Use the following bootstrap script to prep the machine for running the ami tools and api. The script after the bootstrap will setup a volume snapshot ready to be registered as an AMI.

You will require the following packages, if they are not already installed on the AMI:

openssh-client 
openssh-server 
curl 
unzip 
wget 
rsync 
parted 
bc 
sudo 
ruby 
libopenssl-ruby1.8 
openjdk-6-jre-headless 

This script bootstraps your AWS environment, you can skip this if you already have this done, but you will need to modify the next script to match your environment:

cat > aws_bootstrap.sh << \BOOTEOF
#!/bin/bash
#EC2 AMI Tools 
cd /tmp
wget http://s3.amazonaws.com/ec2-downloads/ec2-ami-tools.zip -O ec2-ami-tools.zip
cd /usr/local
unzip /tmp/ec2-ami-tools.zip
ln -s `find . -type d -name ec2-ami-tools-*` ec2-ami-tools
chmod -R go-rwsx ec2*
rm -rf /tmp/ec2*


#EC2 API Tools
cd /tmp
wget http://s3.amazonaws.com/ec2-downloads/ec2-api-tools.zip
cd /usr/local
unzip /tmp/ec2-api-tools.zip
ln -s `find . -type d -name ec2-api-tools*` ec2-api-tools
chmod -R go-rwsx ec2*
rm -rf /tmp/ec2*


mkdir ~/.aws
cat > ~/.aws/cert.pem <<\EOF
-----BEGIN CERTIFICATE-----
<snip - insert the text from your certificate>
-----END CERTIFICATE-----
EOF
cat > ~/.aws/pk.pem <<\EOF
-----BEGIN PRIVATE KEY-----
<snip - insert the text from your private key>
-----END PRIVATE KEY-----
EOF


cat >~/.aws/aws.sh <<\EOF
#!/bin/bash
export EC2_PRIVATE_KEY=/mnt/ec2/pk.pem
export EC2_CERT=/mnt/ec2/cert.pem
export EC2_AMITOOL_HOME=/usr/local/ec2-ami-tools
export EC2_APITOOL_HOME=/usr/local/ec2-api-tools
export EC2_HOME=/usr/local/ec2-api-tools
export JAVA_HOME=/usr
export AMAZON_USER_ID=<snip!!!>
export AWS_ACCESS_KEY_ID=<snip!!!>
export AWS_SECRET_ACCESS_KEY=<snip!!!>
PATH=$EC2_AMITOOL_HOME/bin:$PATH
EOF
chmod -R 600 ~/.aws
chmod o+x ~/.aws/aws.sh
BOOTEOF

This script does the migration. I could have used rsync instead of ec2-bundle, but this makes sure the resulting image looks like what Amazon is expecting.

cat > migrate2ebs.sh << \MIGEOF
# Change these to suit your environment
vol_size=20
dev=/dev/sdp
desc="My First EBS Migration"
rm -rf /usr/local/ec*


# Call the environment setup script
. ~/.aws/aws.sh


# Get basic info from instance meta-data
instance_id=`curl -s http://169.254.169.254/latest/meta-data/instance-id`
avail_zone=`curl -s \
http://169.254.169.254/latest/meta-data/placement/availability-zone`


# Create the Volume
vol=`ec2-create-volume -K "$EC2_PRIVATE_KEY" -C "$EC2_CERT" -z "$avail_zone"\
--size $vol_size| cut -f2`


# Attach the volume
ec2attvol "$vol" -K "$EC2_PRIVATE_KEY" -C "$EC2_CERT" -i "$instance_id" -d "$dev"
while [[ "$vol_status" != "attached"  ]];
do
vol_status=`ec2-describe-volumes -K "$EC2_PRIVATE_KEY" -C "$EC2_CERT" "$vol"\
| grep ATTACHMENT | cut -f5`
echo Status of "$vol" : $vol_status
done


# Prepare the volume
mkfs.ext3 "$dev"
mkdir -p /vol
mount "$dev" /vol
rm -rf /mnt/image*
rm -rf /mnt/img-mnt


# Use bundle to create a clean image (we will not upload)
ec2-bundle-vol -c $EC2_CERT -k $EC2_PRIVATE_KEY -u $AMAZON_USER_ID \
-e /vol -d /mnt


# take the clean image and install on the EBS Volume
mount -o loop /mnt/image /mnt/img-mnt
rsync -av /mnt/img-mnt/ /vol/


# Set the fstab up 
cat > /vol/etc/fstab << FSTABEOF
#
<file system>                                 <mount
point>   <type>  <options>       <dump> 
<pass>
proc                                            /proc           proc    defaults        0       0
/dev/sda3                                       None            swap    defaults        0       0
/dev/sdb                                       /               ext3    defaults        0       0
/dev/sda2                                       /mnt            ext3    defaults        0       0
FSTABEOF


# Snapshot the volume. Note the snapshot id for the registration step
umount /vol
ec2addsnap -C $EC2_CERT -K $EC2_PRIVATE_KEY -d $desc $vol
MIGEOF
chmod o+x migrate2ebs.sh

Run the scripts, and note the snapshot id from the last step in the script, you'll need it for the AMI registration

./aws_bootstrap.sh
./migrate2ebs.sh

now all that is left to do is register the snapshot created in the last step

ec2-register -n "MyFirstEBSMigration" -s <snapshotid> -b /dev/sda=ephemeral0 --kernel <kernel> --ramdisk <kernel> --root-device-name /dev/sdb

If everything ran successfully, you should have a brand spanking new EBS based AMI that is a mirror of your old AMI.

This works for us, but your mileage might vary! drop me a line via twitter (@ramarnat) if you have questions.