thor77/hetzner-flatcar

A tool to deploy Flatcar Linux on Hetzner Cloud

hetzner-flatcar

A tool to deploy Flatcar Linux on Hetzner Cloud. Includes transpiling of Container Linux Config and reinstalling maschines on changes.

Build

go build .

Usage

• create a config named config.toml with the values described in configuration.
• create a container linux config template, see template for details
• ./hetzner-flatcar hostname

This tool will establish a SSH session to the rescue os to run the flatcar-install script using goph. For authentication it uses the SSH agent, so ensure the private counterpart to the public key uploaded to Hetzner and referenced in the config is added to your SSH agent.

Configuration

[hcloud]
token = "<hetzner cloud token>"
server_type = "cx11"
location = "nbg1"
ssh_key = "<name of ssh key used for rescue and passed to template>"
private_network = "<private network server is attached to>"

[flatcar]
version = "3139.2.0"
config_template = "ignition.yml.gtpl"
# provide path to custom flatcar-install script
# if not provided will be downloaded from
# https://github.com/flatcar-linux/init/blob/flatcar-master/bin/flatcar-install
# install_script = "custom-install-script"
[flatcar.template_static]
nomad_version = "1.2.6"
consul_version = "1.11.4"

Template

The Container Linux Config template is rendered using text/template and is given this data:

• Server - Server object as returned by Hetzner Cloud API
• SSHKey - SSHKey object of the SSH Key used for rescue boot
• Static - static data from config option flatcar.template_static as map[string]string
• ReadFile(filename string) (string, error) - function to read a local file
• Function(indent int, input string) string - function to indent strings

Afterwards it's transpiled into a Ignition file.

Take a look at the example config for a minimal example just creating a core user with the SSH Key used for rescue boot and setting the hostname to the maschine name.

injecting local files

The container linux config transpiler supports injecting local files (ref). Unfortunately that feature is not usable when not calling it using the CLI, because it relies on the value of a flag to determine the base path to search for files. As an alternative hetzner-flatcar supports the ReadFile template function to inject files into templates.

Example usage:

storage:
  files:
    - path: /etc/LICENSE
      filesystem: root
      contents:
        inline: |
{{ call .ReadFile "LICENSE" | call .Indent 12 }}

Custom template command

Instead of using the native go template, you can also use any other command (for example Helm). To do that provide your custom command in the configuration option flatcar.template_command. It will get passed the hostname as the first argument and Server and SSHKey in YAML format on stdin.

hetzner:
  server:
    name: ...
  sshkey:
    publickey: ...

Example script to render a helm template with a values file based on the hostname:

#!/bin/sh
cat - common.yaml "${1}.yaml" | yq -y . | helm template ignition -f -

Deployment procedure

1. check whether vm with the name given as first parameter already exists
2. create VM (if not already exists)
3. render container linux config template with data from new or existing VM
4. transpile container linux config into ignition file
5. enable rescue boot on VM
6. Startup or reboot VM (into rescue)
7. upload flatcar-install script and rendered ignition config
8. call flatcar-install and reboot