Architecture hints for `Volume`s

[lukasfrank]

Summary

Currently, the Volumes do not offer architecture hints for the ceph-provider in order to populate the correct OS image. This feature is part of ironcore-dev/roadmap#94.

[lukasfrank]

I propose/change the VolumeSpec like in the following, that the MachineEphemeralVolume controller can derive the Architecture from the Machine itself. For explicit created Volumes there are multiple cases where I propose to go with the bold solutions:

• If multi-arch image is provided and no architecture hint is set
  • put the volume in Error state
  • keep the volume in Pending and indicate the problem via event
  • default to a specific architecture
• If multi-arch image is provided and architecture hint is set but the layer is not present
  • put the volume in Error state
• If single-arch image is provided
  • indicate the problem via event in case of missmatch
  • ignore architecture hint

Current API definition:

// VolumeSpec defines the desired state of Volume
type VolumeSpec struct {
	.... 
	// VolumeDataSource is the source where the storage for the Volume resides at.
	VolumeDataSource `json:",inline"`
}

// VolumeDataSource specifies the source to use for a Volume.
type VolumeDataSource struct {
	// VolumeSnapshotRef instructs to use the specified VolumeSnapshot as the data source.
	VolumeSnapshotRef *corev1.LocalObjectReference `json:"volumeSnapshotRef,omitempty"`
	// OSImage is an optional os image to bootstrap the volume.
	OSImage *string `json:"osImage,omitempty"`
}

Proposed changes:

// VolumeSpec defines the desired state of Volume
type VolumeSpec struct {
         ....
	//TODO should that be inlined?
	VolumeDataSource `json:",inline"`
}

// VolumeDataSource specifies the source to use for a Volume.
type VolumeDataSource struct {
	// VolumeSnapshotRef instructs to use the specified VolumeSnapshot as the data source.
	VolumeSnapshotRef *corev1.LocalObjectReference `json:"volumeSnapshotRef,omitempty"`
	// OS defines an optional os image to bootstrap the volume.
	OS *OSDataSource `json:"os,omitempty"`
}

type OSDataSource struct {
	// Image is an optional image to bootstrap the volume with.
	Image string `json:"image,omitempty"`

	// Architecture defines the architecture of the OS which should be used
	Architecture *string `json:"architecture,omitempty"`
}