Cloud-config Reference

Node OS images build using the Elemental Toolkit are expected to be initialized and configured by using yip. Yip is a small utility to apply a set of actions and configurations to the system described with yaml files. Yip is integrated and consumed as a library within the elemental client binary (see elemental run-stage --help). Yip groups the configurations and actions to apply in arbitrary stages, for instance the elemental run-stage network command call would only apply defined actions and configuration for the stage named network. Note from Yip perspective stages can be run at any time as they are simply grouping a set of actions under an arbitrary name.

Elemental Toolkit integrates five predefined stages into the OS boot process.

pre-rootfs: this stage runs on early boot inside the init ram disk, just before mounting the root device (typically at /sysroot). This stage can be used to define first-boot steps that are required before mounting the root device. A good example is expanding the root device partition. Executed as part of the initrd-root-device.target.
rootfs: this stage runs on early boot inside the init ram disk, just after mounting the root device (typically at /sysroot). This stage can be used to define first-boot steps like creating new partitions. Ephemeral and persistent paths are typically defined at this stage. Executed as part of the initrd-root-fs.target.
initramfs: this stage runs inside the init ram disk too, but on a later stage just before switching root. This stage runs in a chrooted environment to the actual root device. This stage is handy to set some system parameters that might be relevant to systemd after switching root. For instance, additional systemd unit files could be added here before the systemd from the actual root is executed. Executed as part of the initrd.target.
fs: this stage is the first one executed after switching root and it is executed as part of the sysinit.target which runs once all all local filesystems and mountpoints defined in fstab are mounted and ready.
network: this stage is executed as part of the multi-user.target and after the network-online.target is reached. This stage can be used to run actions and configurations that require network connectivity. For instance this stage is used to run the very first node registration and and installation from a live ISO.
boot: this stage is executed as part of the multi-user.target and before the getty.target. This is the default stage to run cloud-config data provided using the supported cloud-init syntax. See cloud-init compatibility section.

By default, elemental reads the yaml configuration files from the following paths in order: /system/oem, /oem and /usr/local/cloud-config.

In Elemental Operator, all kubernetes resources including a cloud-config field can be expressed in either yip or cloud-init compatible syntax. This includes resources such as MachineRegistration, SeedImage, and ManagedOSImage.

note

In contrast to similar projects such as Cloud Init, Yip does not keep records or caches of executed stages and steps, all stages and its associated configuration is executed at every boot.

Elemental client cloud-config hooks

In addition to the defined cloud-config stages at boot described in the previous section the Elemental client also honors some specific stages, referenced as hooks, to customize the behavior of these subcommands: install, upgrade, reset and build-disk. Each of these subcommands has it's own set of four different cloud-config stages executed at analog phases of the specific subcommand execution.

Hooks are essetially a way to provide permanent changes to system that can't be easily expressed as part of an OCI container or that are not easily achievable with the elemental client configuration options. A good example could be handling the firmware in EFI partition for Raspberry Pi devices.

warning

Note most hooks are executed in the host environment with privileges, so they are potentially destructive operations. In most cases regular cloud-config operations at boot time are sufficient to setup the system. Also to include additional software in an image the preferred option is to build a derivative image and not abuse of hooks to install additional software.

Hook stages

Before stages: before-install, before-upgrade, before-reset, before-disk These stages are executed once the working directories and environment are prepared but before starting the actual action. In install, upgrade and reset steps this happens once all the associated partitions are created and mounted, but before stating the deployment of any image.
After chrooted stages: after-install-chroot, after-upgrade-chroot, after-reset-chroot, after-disk-chroot These stages are executed after deploying the target system into the working area into a chroot environment rooted to the actual deployed image. Since this happens in a chroot env the elemental client analyses the hooks present in the deployed image, not in the host. Only /oem is shared with the host if available.
After stages: after-install, after-upgrade, after-reset, after-disk These stages are executed after deploying the target system into the working area from the host environment. At this stages all partitions are still mounted and available in RW mode. This particular set of stages analyses the hooks present in the host and into the equivalent set of paths chrooted to the deployed image. The hook however is not executed in a chroot environment. This is helpful to provide after-* hooks within the deployed image.
Post stages: post-install, post-upgrade, post-reset, post-disk These stages are executed at end before exiting the command and running a cleanup process. At this stage the image is already deployed and locked in a read-only subvolume or filesystem. Partitions are still mounted at this stage.

note

Note installation hooks are not applied as part of the MachineRegistartion.config.cloud-config. In order to provide installation hooks they can be included as part of the SeedImage.cloud-config, as they need to be present in the installation media. The only exception is after-install-chroot which can be provided as part of a MachineRegistartion.config.cloud-config because the hook runs in the deployed image chroot and by that time cloud-config is already installed into the system.

Configuration syntax

Yip has its own syntax, it essentially requires to define stages and a list of steps for each stage. Steps are executed in order and each step can be a combination different action types (e.g run commands, create files, set hostname, etc.).

Consider the following example:

stages:
  initramfs:
  - name: "Setup users"
    ensure_entities:
    - path: /etc/shadow
      entity: |
          kind: "shadow"
          username: "root"
          password: "root"
  boot:
  - files:
    - path: /tmp/script.sh
      content: |
        #!/bin/sh
        echo "test"
      permissions: 0777
      owner: 1000
      group: 100
  - commands:
    - /tmp/script.sh

In the above exaple there are two stages: initramfs and boot.
The initramfs stage initializes a sample user.
The boot stage includes two steps, one to create an executable script file and a second one that actually runs the script.

Yip also supports *.before and *.after suffix modifiers to any given stage. For instance, running the network stage results into running first network.before stages found in config files and then network and finally network.after.

See the full reference of applicable keys in steps documented in yip project itself.

Below is an example of the above configuration embedded in a MachineRegistration resource.

MachineRegistration example

apiVersion: elemental.cattle.io/v1beta1
kind: MachineRegistration
metadata:
  name: my-nodes
  namespace: fleet-default
spec:
  config:
    cloud-config:
      name: "A registration driven config"
      stages:
        after-install-chroot:
        - name: "Set serial console"
          commands:
          - grub2-editenv /oem/grubenv set extra_cmdline="console=ttyS0"
        initramfs:
        - name: "Setup users"
          ensure_entities:
          - path: /etc/shadow
            entity: |
                kind: "shadow"
                username: "root"
                password: "root"
        boot:
        - files:
          - path: /tmp/script.sh
            content: |
              #!/bin/sh
              echo "test"
            permissions: 0777
            owner: 1000
            group: 100
        - commands:
          - /tmp/script.sh
    elemental:
      install:
        reboot: true
        device: /dev/sda
        debug: true
  machineName: my-machine
  machineInventoryLabels:
    element: fire

Compatibility with Cloud Init format

A subset of the official cloud-config spec is implemented by yip. More specific the supported cloud-init keys are: users, ssh_authorized_keys, runcmd, hostname and write_files are implemented.

If a yaml file starts with #cloud-config it is parsed as a standard cloud-init, associated it to the yip boot stage. For example:

#cloud-config
users:
- name: "bar"
  passwd: "foo"
  groups: "users"
  homedir: "/home/foo"
  shell: "/bin/bash"
  ssh_authorized_keys:
  - faaapploo

# Assigns these keys to the first user in users or root if there
# is none
ssh_authorized_keys:
- asdd

# Run these commands once the system has fully booted
runcmd:
- foo

# Write arbitrary files
write_files:
- encoding: b64
  content: CiMgVGhpcyBmaWxlIGNvbnRyb2xzIHRoZSBzdGF0ZSBvZiBTRUxpbnV4
  path: /foo/bar
  permissions: "0644"
  owner: "bar"

Below is an example of the above configuration embedded in a MachineRegistration resource.

MachineRegistration example

apiVersion: elemental.cattle.io/v1beta1
kind: MachineRegistration
metadata:
  name: my-nodes
  namespace: fleet-default
spec:
  config:
    cloud-config:
      users:
      - name: "bar"
        passwd: "foo"
        groups: "users"
        homedir: "/home/foo"
        shell: "/bin/bash"
        ssh_authorized_keys:
        - faaapploo
      ssh_authorized_keys:
      - asdd
      runcmd:
      - foo
      write_files:
      - encoding: b64
        content: CiMgVGhpcyBmaWxlIGNvbnRyb2xzIHRoZSBzdGF0ZSBvZiBTRUxpbnV4
        path: /foo/bar
        permissions: "0644"
        owner: "bar"
    elemental:
      install:
        reboot: true
        device: /dev/sda
        debug: true
  machineName: my-machine
  machineInventoryLabels:
    element: fire

Elemental client cloud-config hooks​

Hook stages​

Configuration syntax​

Compatibility with Cloud Init format​

Elemental client cloud-config hooks

Hook stages

Configuration syntax

Compatibility with Cloud Init format