Build Flatcar Snapshots on Hetzner Cloud with Packer

Important

This version of the README describes the process to build & test Hetzner OEM images using the Draft PR flatcar/scripts#1880. If you are a user looking to install Flatcar on Hetzner Cloud right now, you can check out the main branch of this repo.

Requirements

• Hetzner Cloud API Token
• Packer
• Hetzner Cloud CLI (hcloud)

Building Image

See https://www.flatcar.org/docs/latest/reference/developer-guides/sdk-modifying-flatcar/

./build_packages
./build_image --replace
./image_to_vm --format hetzner

Building Snapshots

In Hetzner Cloud, you can create a "Snapshot" of your server's disk. You can then use these snapshots to create new servers.

We will use Packer and the flatcar-install script to write the image we built in the previous step to the disk and then create a snapshot.

$ git clone --branch oem-image https://github.com/apricote/flatcar-packer-hcloud.git
$ cd flatcar-packer-hcloud
$ export HCLOUD_TOKEN=<Your Hetzner Cloud API Token>
$ packer init .

# This will build the Snapshot for x86. You need to specify the path to your local image file.
$ packer build . -var image_path=/path/to/flatcar_production_hetzner_image.bin.bz2
# ... Takes a few minutes
==> Builds finished. The artifacts of successful builds are:
--> hcloud.x86: A snapshot was created: 'flatcar-x86' (ID: 157132241)

$ hcloud image list --type=snapshot --selector=os=flatcar
ID          TYPE       NAME   DESCRIPTION   ARCHITECTURE   IMAGE SIZE   DISK SIZE   CREATED                        DEPRECATED
157132241   snapshot   -      flatcar-x86   x86            0.47 GB      20 GB       Sat Mar 30 16:48:22 CET 2024   -

Create a Server

You can now create a new server from the snapshot. Not every feature might automatically work, as the snapshot is missing the functionality from hc-utils. Configuring SSH Keys and User Data (Ignition) will work as expected.

# Get ID of the most recent flatcar snapshot for x86
$ SNAPSHOT_ID=$(hcloud image list --type=snapshot --selector=os=flatcar --architecture=x86 -o=columns=id -o noheader --sort=created:desc | head -n1)

# Create a new server
# If you have, you can specify an Ignition config with `--user-data-from-file ignition-user.json`
$ hcloud server create --name flatcar-test --image $SNAPSHOT_ID --type cx11 --ssh-key <your-key>
# Wait about a minute or two for the server to be started

# Now you can login, the following is a helper that calls `ssh` with the public ipv4 address of the server
$ hcloud server ssh -u core flatcar-test