January 01, 2021

Linux AMIs from AWS are typically are 8GB in size. This leaves around 80% disk space unused if there are not much software is installed and if the data is another volume.

There are some advantages creating a smaller root volume.

  • Lower cost. GP3 volumes are cheaper now, but it saves money if there are lot of instances.
  • Faster AMI creation.
  • You can always increase size of the root volume when needed, but decreasing the size is not possible.

To do this I tried several methods.

  • Simply rysnc another snapshot does not work. how ever this can work for non root volume with data.
  • dd copy or manually creating the file system and copying the files failed with file system error on boot.
  • Creating a raw image manually.

Unfortunately it is not easy to do, only way I found that worked was creating image using fai. Even then there are configurations to be created. Fortunately the debian team shares the code they used create the debain AMI images on their git repo.

First setup a instance with debian buster AMI, make sure to use x64 one.

Or use the following terraform script to create the setup that I used. It will create a t3a.nano spot instance with a empty 1GB volume.

provider "aws" {
  region = "eu-central-1" #change the region
  profile = "" #add your profile name

resource "aws_spot_instance_request" "fai_server" {
  ami                    =
  instance_type          = "t3a.nano"
  spot_price             = "0.0016" #check the price when you run
  availability_zone      = data.aws_availability_zones.available.names[1]
  key_name               = "" #add your key name
  spot_type              = "one-time"
  wait_for_fulfillment   = true

resource "aws_ebs_volume" "ami_volume" {
  availability_zone = aws_spot_instance_request.fai_server.availability_zone
  size              = 1
  type              = "gp3"
  tags = {
    Name = "1gb-ami"

resource "aws_volume_attachment" "ebs_attach_ami_vol" {
  device_name = "/dev/xvdf"
  volume_id   =
  instance_id = aws_spot_instance_request.fai_server.spot_instance_id

data "aws_ami" "debian_buser" {
  most_recent = true
  owners      = ["136693071363"]

  filter {
    name   = "name"
    values = ["debian-10-amd64-*-*"]

data "aws_availability_zones" "available" {
  state = "available"

First update the apt cache

sudo apt update

Install fai server and the required tools

sudo apt install fai-server fai-setup-storage dosfstools

Get the config space configuration the debian team is using

wget -O debian-cloud-images-master.tar.gz

unzip the tar file

tar -xzf debian-cloud-images-master.tar.gz

In the debain teams configuration, there are some files that we don’t need. We need to remove them or the process will fail.

remove the following files

rm debian-cloud-images-master-config_space/config_space/hooks/tests.CLOUD
rm debian-cloud-images-master-config_space/config_space/scripts/LAST/30-manifest
rm debian-cloud-images-master-config_space/config_space/scripts/LAST/40-info

Then run the following command to create the the image.

sudo /usr/sbin/fai-diskimage --verbose --hostname debian --class DEBIAN,CLOUD,TYPE_DEV,BUSTER,EC2,IPV6_DHCP,AMD64,GRUB_CLOUD_AMD64,LINUX_IMAGE_CLOUD,LAST --size 1G --cspace /home/admin/debian-cloud-images-master-config_space/config_space image_buster_ec2_amd64.raw

To find more info about the above command see

if successful you will get a .raw file and a notice that it was successfully created

Now dd copy the raw file to the empty volume.

sudo dd if=image_buster_ec2_amd64.raw of=/dev/nvme1n1 bs=512k

check the file system of the volume

sudo partx --show /dev/nvme1n1

Now create a snapshot and register a AMI from the 1GB volume. Launch a instance from the AMI and see if it works.

If anyone knows a better way, feel free to contact me at twitter