Development notes

Guidelines when developing Kairos

Here you can find development notes intended for maintainers and guidance for new contributors.

Repository structure

Kairos uses earthly as a build system instead of Makefiles. This ensures that despite the environment you should be able to build Kairos seamlessly. To track external packages (like kernels, additional binaries, and so on) which follow their own versioning luet is used and there is a separate repository with package building specifications.

  • The Kairos repository contains the kairos-agent code, the OS definitions (Dockerfiles) and configuration. The releases generate core ISOs without any Kubernetes engine.
  • The packages repository contains package specifications used by kairos while building OS images.
  • The provider-kairos repository contains the kairos provider component which uses the SDK to bring up a Kubernetes cluster with k3s. It uses images from kairos core to remaster images with k3s and the provider embedded. This allows to automatically bootstrap Kubernetes cluster. Note, Kairos core in runtime can be extended to add providers or deploy automatically images with the embedded provider.

Build Kairos

To build Kairos you need only Docker installed locally, and there is a convenience script in the root of the repository ( which wraps earthly inside Docker to avoid to install locally which can be used instead of earthly (e.g. ./ +iso ...). However, for daily development, it is strongly suggested to install it in your workstation. The script runs earthly in a container, and as such there are limitations on image caching between builds.

To build a Kairos ISO, you need to specify the flavor. For example, to build Kairos Alpine with earthly installed locally:

earthly -P +iso --FLAVOR=alpine

This will build a container image from scratch and create an ISO which is ready to be booted.

Note earthly targets are prefixed with + while variables are passed as flags, and ARGS can be passed as parameters with --.

Adding flavors

Every source image used as a flavor is inside the images folder in the top-level directory. Any Dockerfile have the extension corresponding to the flavor which can be used as an argument for earthly builds (you will find a Dockerfile.alpine that will be used by our earthly -P +iso --FLAVOR=alpine above).

To add a flavor is enough to create a Dockerfile corresponding to the flavor and check if any specific setting is required for it in the +framework target.

Generally to add a flavor the image needs to have installed:

  • An init system (systemd or openRC are supported)
  • Kernel
  • GRUB
  • rsync

If you are building a flavor without Earthly, be sure to consume the packages from our repository to convert it to a Kairos-based version.

Bumping packages

Let’s assume there is some change you introduce in a package consumed by kairos (e.g. kcrypt). In order to build a kairos image with the updated package, first tag the repository (kcrypt in our example). Then trigger the auto-bump pipeline on the packages repository. This should create at least on PR which bumps the desired package to the latest tag. It may also create more PRs if other packages had new tags recently. When PR passes CI, merge it. Next, in order to bump the packages on kairos, manually trigger the bump-repos pipeline. This will automatically open a PR on the kairos repository which can be merged when it passes CI. After this, any images produced by the kairos repository, will have the latest version of the package(s).

New controllers

Kairos-io adopts operator-sdk.

To install operator-sdk locally you can use the kairos repositories:

  1. Install Luet: curl | sudo sh
  2. Enable the Kairos repository locally: luet repo add kairos --url --type docker
  3. Install operator-sdk: luet install -y utils/operator-sdk

Create the controller

Create a directory and let’s init our new project it with the operator-sdk:

$ mkdir kairos-controller-foo
$ cd kairos-controller-foo
$ operator-sdk init --domain --repo

Create a resource

To create a resource boilerplate:

$ operator-sdk create api --group <groupname> --version v1alpha1 --kind <resource> --resource --controller

Convert to a Helm chart

operator-sdk does not have direct support to render Helm charts (see issue), we use kubesplit to render Helm templates by piping kustomize manifests to it. kubesplit will split every resource and add a minimal helm templating logic, that will guide you into creating the Helm chart.

If you have already enabled the kairos repository locally, you can install kubesplit with:

$ luet install -y utils/kubesplit

Test with Kind

Operator-sdk will generate a Makefile for the project. You can add the following and edit as needed to add kind targets:


	kind create cluster --name ${CLUSTER_NAME} || true
	$(MAKE) kind-setup-image

kind-setup-image: docker-build
	kind load docker-image --name $(CLUSTER_NAME) ${IMG}

.PHONY: test_deps
	go install -mod=mod
	go install

.PHONY: unit-tests
unit-tests: test_deps
	$(GINKGO) -r -v  --covermode=atomic --coverprofile=coverage.out -p -r ./pkg/...


kind-e2e-tests: ginkgo kind-setup install undeploy deploy e2e-tests

Last modified April 25, 2023: Move docs into root (f4e3511)