shrink-ec2-windows-root-volume.sh

ec2_profile="taskcluster"
ec2_region="us-east-1"
target_instance_id="i-00000000000000000"
shrink_instance_id="i-99999999999999999"

# determine the device name of the root volume (usually "/dev/sda1")
target_instance_device=$(aws ec2 describe-instance-attribute --profile ${ec2_profile} --region ${ec2_region} --instance-id ${target_instance_id} --attribute rootDeviceName | jq -r '.RootDeviceName.Value')

# determine the ec2 volume id of the root volume
large_volume_id=$(aws ec2 describe-instance-attribute --profile ${ec2_profile} --region ${ec2_region} --instance-id ${target_instance_id} --attribute blockDeviceMapping | jq -r '.BlockDeviceMappings[] | select(.DeviceName == "${target_instance_device}") | .Ebs.VolumeId')

# detach the large volume from the target instance
aws ec2 detach-volume --profile ${ec2_profile} --region ${ec2_region} --volume-id ${large_volume_id}

# determine the availability zone of the target host
target_instance_availability_zone=$(aws ec2 describe-instances --profile ${ec2_profile} --region ${ec2_region} --instance-ids ${target_instance_id} | jq -r '.Reservations[0].Instances[0].Placement.AvailabilityZone')

# create a new small volume in the availability zone of the target host
small_volume_id=$(aws ec2 create-volume --profile ${ec2_profile} --region ${ec2_region} --availability-zone ${target_instance_availability_zone} --size 30 --volume-type gp2 | jq -r '.VolumeId')

# attach the large volume to the shrink host as /dev/sdf
aws ec2 attach-volume --profile ${ec2_profile} --region ${ec2_region} --volume-id ${large_volume_id} --instance-id ${shrink_instance_id} --device /dev/sdf

# attach the small volume to the shrink host as /dev/sdg
aws ec2 attach-volume --profile ${ec2_profile} --region ${ec2_region} --volume-id ${small_volume_id} --instance-id ${shrink_instance_id} --device /dev/sdg

# determine the public dns name of the shrink host
shrink_instance_dns_name=$(aws ec2 describe-instances --profile ${ec2_profile} --region ${ec2_region} --instance-ids ${shrink_instance_id} | jq -r '.Reservations[0].Instances[0].PublicDnsName')

# determine the ssh key name of the shrink host
shrink_instance_key_name=$(aws ec2 describe-instances --profile ${ec2_profile} --region ${ec2_region} --instance-ids ${shrink_instance_id} | jq -r '.Reservations[0].Instances[0].KeyName')

# ssh to the shrink host and copy the large volume to the small one
ssh -i ~/.ssh/${shrink_instance_key_name} ec2-user@${shrink_instance_dns_name} sudo dd if=/dev/sdf of=/dev/sdg bs=1M

# detach the small volume from the shrink host
aws ec2 detach-volume --profile ${ec2_profile} --region ${ec2_region} --volume-id ${small_volume_id}

# attach the small volume to the target host
aws ec2 attach-volume --profile ${ec2_profile} --region ${ec2_region} --volume-id ${small_volume_id} --instance-id ${target_instance_id} --device ${target_instance_device}

based on http://nybbl.blogspot.co.uk/2013/08/shrinking-windows-boot-drive-in-aws.html