[DOC] Document JSON for default-disks-config

[guettli]

What's the document you plan to update? Why? Please describe

The documentation "customizing default disk and node config" shows this snippet:

node.longhorn.io/default-disks-config: 
'[
    { 
        "path":"/mnt/disk1",
        "allowScheduling":true
    },
    {   
        "name":"fast-ssd-disk", 
        "path":"/mnt/disk2",
        "allowScheduling":false,
        "storageReserved":10485760,
        "tags":[
            "ssd",
            "fast"
        ]
    }
]'

I am missing in the docs a link to the specification about this data format. Which values are allowed in this json snippet?

Please update the page or add a hyperlink to the schema definition.

Thank you.

[ejweber]

I looked into this a bit, and unfortunately, we're simply not well set up to provide a link like you are requesting. The annotation is meant to essentially contain a JSON formatted list of DiskSpec objects.

Viewed in Go code:

https://github.com/longhorn/longhorn-manager/blob/b615732bc75d5513a7f3289a667af1f06a55af1d/k8s/pkg/apis/longhorn/v1beta2/node.go#L81-L98

type DiskSpec struct {
	// +kubebuilder:validation:Enum=filesystem;block
	// +optional
	Type DiskType `json:"diskType"`
	// +optional
	Path string `json:"path"`
	// +kubebuilder:validation:Enum="";auto;aio
	// +optional
	DiskDriver DiskDriver `json:"diskDriver"`
	// +optional
	AllowScheduling bool `json:"allowScheduling"`
	// +optional
	EvictionRequested bool `json:"evictionRequested"`
	// +optional
	StorageReserved int64 `json:"storageReserved"`
	// +optional
	Tags []string `json:"tags"`
}

Viewed in the nodes.longhorn.io CRD:

longhorn/chart/templates/crds.yaml

Lines 2369 to 2394 in e759608

	properties:
	allowScheduling:
	type: boolean
	diskDriver:
	enum:
	- ""
	- auto
	- aio
	type: string
	diskType:
	enum:
	- filesystem
	- block
	type: string
	evictionRequested:
	type: boolean
	path:
	type: string
	storageReserved:
	format: int64
	type: integer
	tags:
	items:
	type: string
	type: array
	type: object

However, instead of a map/dictionary of name to DiskSpec object, as seen with a kubectl get -oyaml, the annotation takes a list of DiskSpec objects with an additional name field. So you can either add an extra name field to each DiskSpec (as in "name":"fast-ssd-disk", from the second item in the doc example), or omit the name field (as in the first item in the doc example).

The example already includes all valid fields for a v1 volume that it makes sense to set.

[guettli]

@ejweber thank you for your reply. This answers the above question, and leads me to a new follow-up question: #9057 Do you have an answer for that?