The Controller

The controller component (which is part of the manager) monitors custom resources of kind VirtualMachine. It creates or modifies other resources in the cluster as required to get the VM defined by the CR up and running.

Here is the sample definition of a VM from the “local-path” example:

apiVersion: "vmoperator.jdrupes.org/v1"
kind: VirtualMachine
metadata:
  namespace: vmop-demo
  name: test-vm
spec:
  guestShutdownStops: false

  vm:
    state: Running
    maximumCpus: 4
    currentCpus: 2
    maximumRam: 8Gi
    currentRam: 4Gi
  
    networks:
    - user: {}
    
    disks:
    - volumeClaimTemplate:
        metadata:
          name: system
        spec:
          storageClassName: ""
          selector:
            matchLabels:
              app.kubernetes.io/name: vmrunner
              app.kubernetes.io/instance: test-vm
              vmrunner.jdrupes.org/disk: system
          resources:
            requests:
              storage: 40Gi
    - cdrom:
        image: ""
        # image: https://download.fedoraproject.org/pub/fedora/linux/releases/38/Workstation/x86_64/iso/Fedora-Workstation-Live-x86_64-38-1.6.iso
        # image: "Fedora-Workstation-Live-x86_64-38-1.6.iso"

    display:
      spice:
        port: 5910

Pod management

The central resource created by the controller is a stateful set with the same name as the VM (metadata.name). Its number of replicas is set to 1 if spec.vm.state is “Running” (default is “Stopped” which sets replicas to 0).

Property spec.guestShutdownStops (since 2.2.0) controls the effect of a shutdown initiated by the guest. If set to false (default) a new pod is automatically created by the stateful set controller and the VM thus restarted. If set to true, the runner sets spec.vm.state to “Stopped” before terminating and by this prevents the creation of a new pod.

Defining the basics

How to define the number of CPUs and the size of the RAM of the VM should be obvious from the example. Note that changes of the current number of CPUs and the current RAM size will be propagated to running VMs.

Defining disks

Maybe the most interesting part is the definition of the VM’s disks. This is done by adding one or more volumeClaimTemplates to the list of disks. As its name suggests, such a template is used by the controller to generate a PVC.

The example template does not define any storage. Rather it references some PV that you must have created first. This may be your first approach if you have existing storage from running the VM outside Kubernetes (e.g. with libvirtd).

If you have ceph or some other full fledged storage provider installed and create a new VM, provisioning a disk can happen automatically as shown in this example:

    disks:
    - volumeClaimTemplate:
        metadata:
          name: system
        spec:
          storageClassName: rook-ceph-block
          resources:
            requests:
              storage: 40Gi

The disk will be available as “/dev/name-disk” in the VM, using the string from .volumeClaimTemplate.metadata.name as name. If no name is defined in the metadata, then “/dev/disk-n” is used instead, with n being the index of the disk definition in the list of disks.

Apart from appending “-disk” to the name (or generating the name) the volumeClaimTemplate is simply copied into the stateful set definition for the VM (with some additional labels, see below). The controller for stateful sets appends the started pod’s name to the name of the volume claim templates when it creates the PVCs. Therefore you’ll eventually find the PVCs as “name-disk-vmName-0” (or “disk-n-vmName-0”).

PVCs generated from stateful set definitions are considered “precious” and never removed automatically. This behavior fits perfectly for VMs. Usually, you do not want the disks to be removed automatically when you (maybe accidentally) remove the CR for the VM. To simplify the lookup for an eventual (manual) removal, all PVCs are labeled with “app.kubernetes.io/name: vm-runner”, “app.kubernetes.io/instance: vmName”, and “app.kubernetes.io/managed-by: vm-operator”.

Choosing an image for the runner

The image used for the runner can be configured with spec.image. This is a mapping with either a single key source or a detailed configuration using the keys repository, path etc.

Currently two runner images are maintained. One that is based on Arch Linux (ghcr.io/mnlipp/org.jdrupes.vmoperator.runner.qemu-arch) and a second one based on Alpine (ghcr.io/mnlipp/org.jdrupes.vmoperator.runner.qemu-alpine).

Starting with release 1.0, all versions of runner images and managers that have the same major release number are guaranteed to be compatible.

Generating cloud-init data

Since: 2.2.0

The optional object .spec.cloudInit with sub-objects .cloudInit.metaData, .cloudInit.userData and .cloudInit.networkConfig can be used to provide data for cloud-init. The data from the CRD will be made available to the VM by the runner as a vfat formatted disk (see the description of NoCloud).

If .metaData.instance-id is not defined, the controller automatically generates it from the CRD’s resourceVersion. If .metaData.local-hostname is not defined, the controller adds this property using the value from metadata.name.

Note that there are no schema definitions available for .userData and .networkConfig. Whatever is defined in the CRD is copied to the corresponding cloud-init file without any checks. (The introductory comment #cloud-config required at the beginning of .userData is generated automatically by the runner.)

Display secret/password

Since: 2.3.0

You can define a display password using a Kubernetes secret. When you start a VM, the controller checks if there is a secret with labels “app.kubernetes.io/name: vm-runner, app.kubernetes.io/component: display-secret, app.kubernetes.io/instance: vmname” in the namespace of the VM definition. The name of the secret can be chosen freely.

kind: Secret
apiVersion: v1
metadata:
  name: test-vm-display-secret
  namespace: vmop-demo
  labels:
    app.kubernetes.io/name: vm-runner
    app.kubernetes.io/instance: test-vm
    app.kubernetes.io/component: display-secret
type: Opaque
data:
  display-password: dGVzdC12bQ==

If such a secret for the VM is found, the VM is configured to use the display password specified. The display password in the secret can be updated while the VM runs¹. Activating/deactivating the display password while a VM runs is not supported by Qemu and therefore requires stopping the VM, adding/removing the secret and restarting the VM.

VM-Operator

By Michael N. Lipp