gbraad / coreos-assembler

Tooling container to assemble CoreOS-like systems

This container aggregates various tools used to build Fedora CoreOS style systems.

It reuses various upstream tools, such as:

• mantle
• rpm-ostree
• libvirt

A high level goal of this tool is to support two highly related use cases, and to keep them as similar as possible:

• Local development ("test a kernel change")
• Be a production build system orchestrated by an external tool (e.g. Jenkins)

See fedora-coreos-ci as an example pipeline.

Getting started - prerequisites

You can use podman or docker. These examples use podman. Note the container must be privileged, as the build process uses container functionality itself - we're using recursive containers.

Secondly, in order to build VM images, the container must have access to /dev/kvm. If you're running this in a VM, you must enable nested virt. See also GCE nested virt.

Setup

Here we store data in /srv/coreos on our host system. You can choose any directory you like. You should run these commands as root.

$ mkdir /srv/coreos
$ cd /srv/coreos
$ alias coreos-assembler='podman run --rm --net=host -ti --privileged --userns=host -v $(pwd):/srv --workdir /srv quay.io/cgwalters/coreos-assembler'

If you need access to CA certificates on your host (for example, when you need to access a git repo that is not on the public Internet), you can mount in the host certificates as read-only. For example, on a Fedora host the alias would change to:

$ alias coreos-assembler='podman run --rm --net=host -ti --privileged --userns=host -v /etc/pki:/etc/pki:ro -v $(pwd):/srv --workdir /srv quay.io/cgwalters/coreos-assembler'

See this Stack Overflow question for additional discussion.

Initializing

You only need to do this once; it will clone the specified configuration repo, create various directories and also download an installer image (used to make VMs).

$ coreos-assembler init https://github.com/coreos/fedora-coreos-config

The specified git repository will be cloned into /srv/coreos/src/config.

If you're doing something custom, you likely want to fork that upstream repository.

Performing a build

$ coreos-assembler build

Each build will write an OSTree commit into /srv/coreos/repo as well as generate VM images in /srv/coreos/builds/.

Next, rerun coreos-assembler build and notice the system correctly deduces that nothing changed. You can run coreos-assembler fetch to check for updated RPMs.

Running

$ coreos-assembler run

This invokes QEMU on the image in builds/latest. It uses -snapshot, so any changes are thrown away after you exit qemu. To exit, type Ctrl-a x. For more options, type Ctrl-a ?.

Making changes

Currently, the assembler only takes two input files that are from src/config:

• manifest.yaml: An rpm-ostree "manifest" or "treefile", which mostly boils down to a list of RPMs and a set of rpm-md repositories they come from. It also supports postprocess to make arbitrary changes. See the upstream docs.
• image.ks: An Anaconda Kickstart file. Use this to define the base disk image output.

Let's try editing the file src/config/image.ks. Change the root storage line logvol / for example. Rerun coreos-assembler build, and notice that the OSTree commit didn't change, but a new image is generated in builds. When you coreos-assembler run, you'll get it.

Another thing to try is editing src/config/manifest.yaml - add or remove entries from packages. You can also add local rpm-md file:/// repositories.

Development

The container image is built in OpenShift CI.