Proposal for inject/eject CD-ROM

Signed-off-by: Michael Henriksen <[email protected]>

design-proposals/cdrom-inject-eject.md

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+# Overview
+Proposal for for adding inject/eject CD-ROM support to KubeVirt
+
+## Motivation
+In a world where all of our knowledge has been collected, indexed, and can be served up via a network connection, the humble CD-ROM is still a "thing." And to the dedicated hangers-on of this once ubiquitous technology, KubeVirt's CD-ROM support is lacking in a very fundamental way. Today, a user must reboot a VM in order to change the media in a CD-ROM. That is just. not. right. Fortunately, the virtualization technology that underpins KubeVirt has had this functionality for a long time and we can easily plug it into the KubeVirt API to unleash the full power of the CD-ROM
+
+## Goals
+- Extend existing APIs to support inject/eject CD-ROM operations
+- Extend virtctl to have cdrom specific commands
+- Support for PersistentVolumeClaim/DataVolume based disk images
+
+## Non Goals
+- Support for any volume type other than DavaVolume/PersistentVolumeClaim
+
+## Definition of Users
+KubeVirt end user, may not be a namespace/cluster admin
+
+## User Stories
+- As a VM owner, I want to be able to attach a CD-ROM for the purposes of installing an operating system, then be able eject the CD and perform a guest-side reboot to use the operating system.
+- As a VM Owner I want to attach an ISO/CD-ROM from my desktop to the VM without the need to reboot the VM
+- As a VM Owner I want to attach a PVC which contains an ISO to my VM without the need to reboot the VM
+- As a VM Owner I want to be able to "eject" (remove) the ISO/CD from my VM without the need to reboot the VM
+
+## Repos
+kubevirt/kubevirt
+
+# Design
+Like most new features in KubeVirt, the building blocks already exist, just have to wire everything together
+
+## VirtualMachineInstance API
+Currently, every disk in a KubeVirt VM must have a corresponding volume. That restriction will be lifted for CD-ROM disks, i.e., it will be possible to define a VMI that has no corresponding volume for a CD-ROM. For Example:
+
+```yaml
+apiVersion: kubevirt.io/v1
+kind: VirtualMachine
+...
+spec:
+  domain:
+    devices:
+      disks:
+      - cdrom:
+        bus: sata
+      name: cdrom
+      - disk:
+        bus: virtio
+      name: root
+...
+  volumes:
+  - dataVolume:
+      name: fedora-root
+    name: root
+  networks:
+...
+```
+
+## Volume Hotplug Subresource API
+This feature leverages the Volume Hotplug API in order to add/remove disk images in running Pods. Hence, the restriction on PersistentVolumeClaim and DataVolume volume types.
+
+Hotplug operations are wrapped in the `VirtualMachineVolumeRequest` struct which looks like this:
+
+```golang
+type VirtualMachineVolumeRequest struct {
+	// AddVolumeOptions when set indicates a volume should be added. The details
+	// within this field specify how to add the volume
+	AddVolumeOptions *AddVolumeOptions `json:"addVolumeOptions,omitempty" optional:"true"`
+	// RemoveVolumeOptions when set indicates a volume should be removed. The details
+	// within this field specify how to add the volume
+	RemoveVolumeOptions *RemoveVolumeOptions `json:"removeVolumeOptions,omitempty" optional:"true"`
+}
+```
+
+One of `AddVolumeOptions` or `RemoveVolumeOptions` is expected to be set
+
+### AddVolumeOptions
+`AddVolumeOptions` as currently defined:
+
+```golang
+type AddVolumeOptions struct {
+	// Name represents the name that will be used to map the
+	// disk to the corresponding volume. This overrides any name
+	// set inside the Disk struct itself.
+	Name string `json:"name"`
+	// Disk represents the hotplug disk that will be plugged into the running VMI
+	Disk *Disk `json:"disk"`
+	// VolumeSource represents the source of the volume to map to the disk.
+	VolumeSource *HotplugVolumeSource `json:"volumeSource"`
+  DryRun []string `json:"dryRun,omitempty"`
+}
+```
+
+Currently the `disk` field is required. That restriction will be removed. However, when the `addVolume` request is received, we will validate that the corresponding disk is in fact a CD-ROM. The following request will be valid for the VirtualMachine defined above:
+
+```yaml
+addVolumeOptions:
+  name: cdrom
+  volumeSource:
+    persistentVolumeClaim:
+       claimName: windows11-iso
+       hotpluggable: true
+```
+
+### RemoveVolumeOptions
+`RemoveVolumeOptions` as currently defined:
+
+```golang
+type RemoveVolumeOptions struct {
+	// Name represents the name that maps to both the disk and volume that
+	// should be removed
+	Name string `json:"name"`
+	DryRun []string `json:"dryRun,omitempty"`
+}
+```
+
+Since we don't want to remove the CD-ROM when ejecting a disk, a new field will be added to `RemoveVolumeOptions` to specify whether to keep/remove a disk.
+
+```golang
+// DiskRetentionPolicy defines how removevolume subresource API
+// requests should handle the corresponding disk
+type DiskRetentionPolicy string
+
+// DiskRetentionDelete specifies that removevolume should
+// delete the matching disk in the VirtualMachineInstance spec
+const DiskRetentionDelete = "delete"
+
+// DiskRetentionKeep specifies that removevolume should
+// keep the matching disk in the VirtualMachineInstance spec
+const DiskRetentionKeep = "keep"
+```
+
+A `DiskRetentionPolicy` field will be added to `RemoveVolumeOptions`. It will be optional and if excluded, the default is `DiskRetentionDelete` in order to be compatible with old clients
+
+This would be the API for ejecting a CD-ROM in the VirtualMachine defined above
+
+```yaml
+removeVolumeOptions:
+  name: cdrom
+  diskRetentionPolicy: keep
+```
+
+## virtctl
+A couple new convenience commands will be added to virtctl
+
+### virtctl cdrom inject
+Inject a cdrom
+
+```bash
+virtctl cdrom intect myvm --volume-name=cdrom --claim-name=windows-iso
+```
+
+### virtctl cdrom eject
+Eject a cdrom
+
+```bash
+virtctl cdrom eject myvm --volume-name=cdrom --claim-name=windows-iso
+```
+
+## Scalability
+Nothing new here that should effect system scalability
+
+## Update/Rollback Compatibility
+API changes are backwards compatible
+- One field is no longer required
+- One field is new
+
+Rollback would be a problem given the `VirtualMachineInstance` API change. Do we currently support rollback?
+
+## Functional Testing Approach
+- Inject a CD-ROM to a running VM
+- Eject a CD-ROM from a running VM
+- Boot with hotplug CD-ROM, eject, and inject a different CD-ROM
+
+# Implementation Phases
+This is a small change and will be implemented in one phase