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Clone API

The clone.kubevirt.io API Group defines resources for cloning KubeVirt objects. Currently, the only supported cloning type is VirtualMachine, but more types are planned to be supported in the future (see future roadmap below).

Please bear in mind that the clone API is in version v1alpha1. This means that this API is not fully stable yet and that APIs may change in the future.

Prerequesites

Snapshot / Restore

Under the hood, the clone API relies upon Snapshot & Restore APIs. Therefore, in order to be able to use the clone API, please see Snapshot & Restore prerequesites.

Snapshot Feature Gate

Currently, clone API is guarded by Snapshot feature gate. The feature gates field in the KubeVirt CR must be expanded by adding the Snapshot to it.

The clone object

Firstly, as written above, the clone API relies upon Snapshot & Restore APIs under the hood. Therefore, it might be helpful to look at Snapshot & Restore user-guide page for more info.

VirtualMachineClone object overview

In order to initiate cloning, a VirtualMachineClone object (CRD) needs to be created on the cluster. An example for such an object is: 

kind: VirtualMachineClone
apiVersion: "clone.kubevirt.io/v1alpha1"
metadata:
  name: testclone

spec:
  # source & target definitions
  source:
    apiGroup: kubevirt.io
    kind: VirtualMachine
    name: vm-cirros
  target:
    apiGroup: kubevirt.io
    kind: VirtualMachine
    name: vm-clone-target

  # labels & annotations definitions
  labelFilters:
    - "*"
    - "!someKey/*"
  annotationFilters:
    - "anotherKey/*"

  # template labels & annotations definitions
  template:
    labelFilters:
      - "*"
      - "!someKey/*"
    annotationFilters:
      - "anotherKey/*"

  # other identity stripping specs:
  newMacAddresses:
    interfaceName: "00-11-22"
  newSMBiosSerial: "new-serial"

In the next section I will go through the different settings to elaborate them.

Source & Target

The source and target indicate the source/target API group, kind and name. A few important notes:

  • Currently, the only supported kinds are VirtualMachine (of kubevirt.io api group) and VirtualMachineSnapshot ( of snapshot.kubevirt.io api group), but more types are expected to be supported in the future. See "future roadmap" below for more info.

  • The target name is optional. If unspecified, the clone controller will generate a name for the target automatically.

  • The target and source must reside in the same namespace.

Label & Annotation filters

These spec fields are intended to determine which labels / annotations are being copied to the target or stripped away.

The filters are a list of strings. Each string represents a key that may exist at the source. Every source key that matches to one of these values is being copied to the cloned target. In addition, special regular-expression-like characters can be used:

  • Wildcard character (*) can be used to match anything. Wildcard can be only used at the end of the filter.
  • These filters are valid:
    • "*"
    • "some/key*"
  • These filters are invalid:
    • "some/*/key"
    • "*/key"
  • Negation character (!) can be used to avoid matching certain keys. Negation can be only used at the beginning of a filter. Note that a Negation and Wildcard can be used together.
  • These filters are valid:
    • "!some/key"
    • "!some/*"
  • These filters are invalid:
    • "key!"
    • "some/!key"

Setting label / annotation filters is optional. If unset, all labels / annotations will be copied as a default.

Template Label & Template Annotation filters

Some network CNIs such as Kube-OVN or OVN-Kubernetes inject network information into the annotations of a VM. When cloning a VM from a target VM the cloned VM will use the same network. To avoid this you can use template labels and annotation filters.

newMacAddresses

This field is used to explicitly replace MAC addresses for certain interfaces. The field is a string to string map; the keys represent interface names and the values represent the new MAC address for the clone target.

This field is optional. By default, all mac addresses are stripped out. This suits situations when kube-mac-pool is deployed in the cluster which would automatically assign the target with a fresh valid MAC address.

newSMBiosSerial

This field is used to explicitly set an SMBios serial for the target.

This field is optional. By default, the target would have an auto-generated serial that's based on the VM name.

Creating a VirtualMachineClone object

After the clone manifest is ready, we can create it: 

kubectl create -f clone.yaml

To wait for a clone to complete, execute: 

kubectl wait vmclone testclone --for condition=Ready

You can check the clone's phase in the clone's status. It can be one of the following:

  • SnapshotInProgress

  • CreatingTargetVM

  • RestoreInProgress

  • Succeeded

  • Failed

  • Unknown

After the clone is finished, the target can be inspected: 

kubectl get vm vm-clone-target -o yaml

Future roadmap

The clone API is in an early alpha version and may change dramatically. There are many improvements and features that are expected to be added, the most significant goals are:

  • Add more supported source types like VirtualMachineInstace in the future.
  • Add a cross-namespace clone support. This needs to be supported for snapshots / restores first.

Using clones as a "golden VM image"

One of the great things that could be accomplished with the clone API when the source is of kind VirtualMachineSnapshot is to create "golden VM images" (a.k.a. Templates / Bookmark VMs / etc). In other words, the following workflow would be available:

Create a golden image

  • Create a VM

  • Prepare a "golden VM" environment

  • This can mean different things in different contexts. For example, write files, install applications, apply configurations, or anything else.

  • Snapshot the VM

  • Delete the VM

Then, this "golden image" can be duplicated as many times as needed. To instantiate a VM from the snapshot:

  • Create a Clone object where the source would point to the previously taken snapshot
  • Create as many VMs you need

This feature is still under discussions and may be implemented differently then explained here.