Build Flatcar Snapshots on Hetzner Cloud with Packer

Requirements

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

This requires Flatcar version 3941.1.0+.

1. 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 pre-built images from Flatcar CI to the disk and then create a snapshot.

$ git clone 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 and Arm.
$ packer build .
# ... Takes a few minutes
==> Builds finished. The artifacts of successful builds are:
--> hcloud.x86: A snapshot was created: 'flatcar-beta-3941.1.0-x86' (ID: 157132241)
--> hcloud.arm: A snapshot was created: 'flatcar-beta-3941.1.0-arm' (ID: 157132242)

$ hcloud image list --type=snapshot --selector=os=flatcar
ID          TYPE       NAME   DESCRIPTION                 ARCHITECTURE   IMAGE SIZE
167650172   snapshot   -      flatcar-beta-3941.1.0-arm   arm            0.41 GB
167650577   snapshot   -      flatcar-beta-3941.1.0-x86   x86            0.47 GB

2. Create a Server

You can now create a new server from the snapshot. 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

Options

If you need to configure the Flatcar installation or the resulting image, there are a few packer variables that you can set.

• channel: To choose a different Flatcar channel, defaults to beta (as stable does not have Hetzner images yet)
• version: If you want to install a specific version, defaults to current
• labels: See section below

Labels

The labels variable controls the labels that are added to the resulting image. This can be helpful if you use a tool that requires specific image labels, like caph-image-name for cluster-api-provider-hetzner.

The following variables are supported:

• $architecture: The Hetzner Cloud API architecture (x86 or arm).
• $version: The Flatcar version, if you are using current, this is resolved to the actual version in the snapshot.
• $channel: The Flatcar release channel.

The default labels are:

• os=flatcar
• flatcar-channel=$channel
• version=$version
• architecture=$architecture

Known Issues

These features do not work with Flatcar as of version 3941.1.0:

• Volume Automount: You need to mount volumes manually.
• Setting & Resetting Root Passwords: You need to configure an SSH Key through the API or Ignition User Data.