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.

Build Kairos

To build a Kairos OS you only need Docker. 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 Earthly it on 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 a few parameters. For example, to build Kairos Fedora with earthly installed locally:

earthly +iso \
  --FAMILY=rhel \
  --FLAVOR=fedora \
  --BASE_IMAGE=fedora:38 \
  --MODEL=generic \
  • Flavor: is the distribution (the name flavor is kept for backwards compatibility). In this case fedora
  • Family: is a group of distributions that get built in a very similar way. In this case rhel, which can build fedora, rockylinux and almalinux.
  • Flavor release: is the version of the distribution. In this case 38
  • Base image: is the base image used to build the distribution. In this case fedora**:38, but you could use your own image which itself is based on fedora:38.
  • Model: is the hardware model. In this case all ISOs are generic
  • Variant: is the Kairos variant, which can be core or standard. core is the minimal Kairos OS, while standard includes k3s.

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 family which can be used as an argument for earthly builds (you will find a Dockerfile.rhel that will be used by our command 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 on its build 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 February 23, 2024: Reduce sizes and remove warnings (0e183ae)