Provisioning Fedora CoreOS on KubeVirt

This guide shows how to provision new Fedora CoreOS (FCOS) nodes on any KubeVirt-enabled Kubernetes cluster.

Prerequisites

Before provisioning an FCOS machine, you must have an Ignition configuration file containing your customizations. If you do not have one, see Producing an Ignition File.

You also need to have access to a Kubernetes environment with KubeVirt installed.

Referencing the KubeVirt Image

Fedora CoreOS is designed to be updated automatically, with different schedules per stream.

The image for each stream can directly be referenced from the official registry:

  • quay.io/fedora/fedora-coreos-kubevirt:stable

  • quay.io/fedora/fedora-coreos-kubevirt:testing

  • quay.io/fedora/fedora-coreos-kubevirt:next

Launching a VM instance

Given the quay.io/fedora/fedora-coreos-kubevirt images you can create a VMI defnition and combine that with an Ignition config to launch a machine.

In the example below, the Ignition config stored in local file example.ign is exposed to the VMI via a Kubernetes Secret. Learn about various ways to expose userdata to VMIs in the KubeVirt user guide.

If the user prefers, they can use oc instead of kubectl in the following commands.
Creating the secret
kubectl create secret generic ignition-payload --from-file=userdata=example.ign
Launching a VM instance referencing the secret
STREAM="stable" # or "testing" or "next"
cat <<END > vmi.yaml
---
apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
  name: my-fcos
spec:
  domain:
    devices:
      disks:
      - disk:
          bus: virtio
        name: containerdisk
      - disk:
          bus: virtio
        name: cloudinitdisk
      rng: {}
    resources:
      requests:
        memory: 2048M
  volumes:
  - containerDisk:
      image: quay.io/fedora/fedora-coreos-kubevirt:${STREAM}
    name: containerdisk
  - name: cloudinitdisk
    cloudInitConfigDrive:
      secretRef:
        name: ignition-payload
END
kubectl create -f vmi.yaml

Now you should be able to SSH into the instance. If you didn’t change the defaults, the username is core.

Accessing the VM instance using virtctl via ssh
virtctl ssh core@my-fcos

Mirroring the image for use in private registries

If a private registry in air-gapped installations is used, the image can be mirrored to that registry using skopeo.

Mirroring a stable stream FCOS image
skopeo copy docker://quay.io/fedora/fedora-coreos-kubevirt:stable docker://myregistry.io/myorg/fedora-coreos-kubevirt:stable

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