<p>Is there a way to access existing validation specs? For example, I want to be able to set NodeAffinity on my CRD, and would like to just $ref: . I found the entire API here: <a href="https://github.com/kubernetes/kubernetes/blob/master/api/openapi-spec/swagger.json" rel="nofollow noreferrer">https://github.com/kubernetes/kubernetes/blob/master/api/openapi-spec/swagger.json</a>
OR kubectl proxy -> localhost:8001/openapi/v2 (from within my cluster)</p>

<p>I could manually copy paste the api validation schema, but I was wondering if there was a way to automatically reference an existing OpenAPI Validation Spec from within my CRD with $ref. I imagine something like $ref: localhost:8001/openapi/v2/definitions/io.k8s.api.core.v1.NodeAffinity</p>

<p>If this is even possible, will it resolve the inner $refs as well?</p>

<p>For reference, here's what the nodeaffinity definition looks like in the API:</p>

<pre><code>"io.k8s.api.core.v1.NodeAffinity": {
  "description": "Node affinity is a group of node affinity scheduling rules.",
  "properties": {
    "preferredDuringSchedulingIgnoredDuringExecution": {
      "description": "The scheduler will prefer to schedule pods to nodes that satisfy the affinity expressions specified by this field, but it may choose a node that violates one or more of the expressions. The node that is most preferred is the one with the greatest sum of weights, i.e. for each node that meets all of the scheduling requirements (resource request, requiredDuringScheduling affinity expressions, etc.), compute a sum by iterating through the elements of this field and adding \"weight\" to the sum if the node matches the corresponding matchExpressions; the node(s) with the highest sum are the most preferred.",
      "items": {
        "$ref": "#/definitions/io.k8s.api.core.v1.PreferredSchedulingTerm"
      },
      "type": "array"
    },
    "requiredDuringSchedulingIgnoredDuringExecution": {
      "$ref": "#/definitions/io.k8s.api.core.v1.NodeSelector",
      "description": "If the affinity requirements specified by this field are not met at scheduling time, the pod will not be scheduled onto the node. If the affinity requirements specified by this field cease to be met at some point during pod execution (e.g. due to an update), the system may or may not try to eventually evict the pod from its node."
    }
  },
  "type": "object"
},
</code></pre>

<p>(using Operator-SDK with Ansible, incase that matters)</p>

<p>EDIT: (adding a full example to further explain)</p>

<p>I have a CRD called Workshop, and I require validation on certain spec parameters.</p>

<pre><code>apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: workshops.k8s.example.tk
spec:
  group: k8s.example.tk
  names:
    kind: Workshop
    listKind: WorkshopList
    plural: workshops
    singular: workshop
  scope: Namespaced
  subresources:
    status: {}
  validation:
    openAPIV3Schema:
      type: object
      properties:
        spec:
          type: object
          required:
          - workshopID
          properties:
            workshopID: #
              type: string
              description: Unique identifier for this particular virtual 
workshop
              example: d8e8fca2dc0f896fd7cb4cb0031ba249
</code></pre>

<p>Now I need to add a nodeAffinity spec field that will be applied to any pods that live under this CustomResourceDefinition. The validation for it is going to be the exact same as the validation for nodeAffinity in pods.</p>

<p>Let me pull the validation spec that is ALREADY WRITTEN in OpenApi from: <a href="https://github.com/kubernetes/kubernetes/blob/master/api/openapi-spec/swagger.json" rel="nofollow noreferrer">https://github.com/kubernetes/kubernetes/blob/master/api/openapi-spec/swagger.json</a>  and convert it to YAML then add it to my spec.</p>

<pre><code>apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: workshops.k8s.example.tk
spec:
  group: k8s.example.tk
  names:
    kind: Workshop
    listKind: WorkshopList
    plural: workshops
    singular: workshop
  scope: Namespaced
  subresources:
    status: {}
  validation:
    openAPIV3Schema:
      type: object
      properties:
        spec:
          type: object
          required:
          - workshopID
          properties:
            workshopID: #
              type: string
              description: Unique identifier for this particular virtual 
workshop
              example: d8e8fca2dc0f896fd7cb4cb0031ba249
            affinity: #
          type: object
          properties:
            nodeAffinity: #
              description: Node affinity is a group of node affinity scheduling rules.
              type: object
              properties:
                preferredDuringSchedulingIgnoredDuringExecution:
                  description: The scheduler will prefer to schedule pods to nodes that satisfy
                    the affinity expressions specified by this field, but it may choose a node that
                    violates one or more of the expressions. The node that is most preferred is
                    the one with the greatest sum of weights, i.e. for each node that meets all
                    of the scheduling requirements (resource request, requiredDuringScheduling affinity
                    expressions, etc.), compute a sum by iterating through the elements of this
                    field and adding "weight" to the sum if the node matches the corresponding matchExpressions;
                    the node(s) with the highest sum are the most preferred.
                  type: array
                  items:
                    description: An empty preferred scheduling term matches all objects with implicit
                      weight 0 (i.e. it's a no-op). A null preferred scheduling term matches no
                      objects (i.e. is also a no-op).
                    type: object
                    required:
                    - weight
                    - preference
                    properties:
                      preference:
                        description: A node selector term, associated with the corresponding weight.
                          A null or empty node selector term matches no objects. The requirements
                          of them are ANDed. The TopologySelectorTerm type implements a subset of
                          the NodeSelectorTerm.
                        type: object
                        properties:
                          matchExpressions:
                            description: A list of node selector requirements by node's labels.
                            type: array
                            items:
                              description: A node selector requirement is a selector that contains
                                values, a key, and an operator that relates the key and values.
                              type: object
                              required:
                              - key
                              - operator
                              properties:
                                key:
                                  description: The label key that the selector applies to.
                                  type: string
                                operator:
                                  description: Represents a key's relationship to a set of values.
                                    Valid operators are In, NotIn, Exists, DoesNotExist. Gt, and
                                    Lt.
                                  type: string
                                values:
                                  description: An array of string values. If the operator is In
                                    or NotIn, the values array must be non-empty. If the operator
                                    is Exists or DoesNotExist, the values array must be empty. If
                                    the operator is Gt or Lt, the values array must have a single
                                    element, which will be interpreted as an integer. This array
                                    is replaced during a strategic merge patch.
                                  type: array
                                  items:
                                    type: string
                          matchFields:
                            description: A list of node selector requirements by node's fields.
                            type: array
                            items:
                              description: A node selector requirement is a selector that contains
                                values, a key, and an operator that relates the key and values.
                              type: object
                              required:
                              - key
                              - operator
                              properties:
                                key:
                                  description: The label key that the selector applies to.
                                  type: string
                                operator:
                                  description: Represents a key's relationship to a set of values.
                                    Valid operators are In, NotIn, Exists, DoesNotExist. Gt, and
                                    Lt.
                                  type: string
                                values:
                                  description: An array of string values. If the operator is In
                                    or NotIn, the values array must be non-empty. If the operator
                                    is Exists or DoesNotExist, the values array must be empty. If
                                    the operator is Gt or Lt, the values array must have a single
                                    element, which will be interpreted as an integer. This array
                                    is replaced during a strategic merge patch.
                                  type: array
                                  items:
                                    type: string
                      weight:
                        description: Weight associated with matching the corresponding nodeSelectorTerm,
                          in the range 1-100.
                        type: integer
                        format: int32
                requiredDuringSchedulingIgnoredDuringExecution:
                  description: If the affinity requirements specified by this field are not met
                    at scheduling time, the pod will not be scheduled onto the node. If the affinity
                    requirements specified by this field cease to be met at some point during pod
                    execution (e.g. due to an update), the system may or may not try to eventually
                    evict the pod from its node. A node selector represents the union of the results
                    of one or more label queries over a set of nodes; that is, it represents the
                    OR of the selectors represented by the node selector terms.
                  type: object
                  required:
                  - nodeSelectorTerms
                  properties:
                    nodeSelectorTerms:
                      description: Required. A list of node selector terms. The terms are ORed.
                      type: array
                      items:
                        description: A null or empty node selector term matches no objects. The
                          requirements of them are ANDed. The TopologySelectorTerm type implements
                          a subset of the NodeSelectorTerm.
                        type: object
                        properties:
                          matchExpressions:
                            description: A list of node selector requirements by node's labels.
                            type: array
                            items:
                              description: A node selector requirement is a selector that contains
                                values, a key, and an operator that relates the key and values.
                              type: object
                              required:
                              - key
                              - operator
                              properties:
                                key:
                                  description: The label key that the selector applies to.
                                  type: string
                                operator:
                                  description: Represents a key's relationship to a set of values.
                                    Valid operators are In, NotIn, Exists, DoesNotExist. Gt, and
                                    Lt.
                                  type: string
                                values:
                                  description: An array of string values. If the operator is In
                                    or NotIn, the values array must be non-empty. If the operator
                                    is Exists or DoesNotExist, the values array must be empty. If
                                    the operator is Gt or Lt, the values array must have a single
                                    element, which will be interpreted as an integer. This array
                                    is replaced during a strategic merge patch.
                                  type: array
                                  items:
                                    type: string
                          matchFields:
                            description: A list of node selector requirements by node's fields.
                            type: array
                            items:
                              description: A node selector requirement is a selector that contains
                                values, a key, and an operator that relates the key and values.
                              type: object
                              required:
                              - key
                              - operator
                              properties:
                                key:
                                  description: The label key that the selector applies to.
                                  type: string
                                operator:
                                  description: Represents a key's relationship to a set of values.
                                    Valid operators are In, NotIn, Exists, DoesNotExist. Gt, and
                                    Lt.
                                  type: string
                                values:
                                  description: An array of string values. If the operator is In
                                    or NotIn, the values array must be non-empty. If the operator
                                    is Exists or DoesNotExist, the values array must be empty. If
                                    the operator is Gt or Lt, the values array must have a single
                                    element, which will be interpreted as an integer. This array
                                    is replaced during a strategic merge patch.
                                  type: array
                                  items:
                                    type: string
</code></pre>

<p>Wow, for just one field (and its sub fields) to be validated, my CRD definition has grown by 100+ lines, all just to reimplement something that already exists in the Kubernetes-native pod api definition. It also took about 15 minutes to manually copy paste and resolve all the references in the Kubernetes spec by hand. Wouldn't it make so much sense to either:</p>

<p>A) Store this long API spec in an external file, and use $ref: externalfile.json to pull it in to keep my CRD small and clean.</p>

<p>OR BETTER YET</p>

<p>B) Insert the actual Kubernetes-native validation spec that ALREADY EXISTS with a $ref tag like this:</p>

<pre><code>apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: workshops.k8s.example.tk
spec:
  group: k8s.example.tk
  names:
    kind: Workshop
    listKind: WorkshopList
    plural: workshops
    singular: workshop
  scope: Namespaced
  subresources:
    status: {}
  validation:
    openAPIV3Schema:
      type: object
      properties:
        spec:
          type: object
          required:
          - workshopID
          properties:
            workshopID: #
              type: string
              description: Unique identifier for this particular virtual 
workshop
              example: d8e8fca2dc0f896fd7cb4cb0031ba249
            affinity:
              type: object
              properties:
                nodeAffinity:
                  $ref: &lt;kubernetes-api&gt;/openapi/v2#/definitions/io.k8s.api.core.v1.NodeAffinity
</code></pre>

<p>Back down to 30 or so lines of code, AND the validation spec stays up-to-date with Kubernetes native validation, since it's pulling the information from Kubernetes API itself. According to this, $ref should be supported in doing this: <a href="https://swagger.io/docs/specification/using-ref/#syntax" rel="nofollow noreferrer">https://swagger.io/docs/specification/using-ref/#syntax</a></p>

<p>There unfortunately isn't a way to do nicely this currently. We solved the problem by writing <a href="https://gist.github.com/danrspencer/f695a22b15b1e4e3b3cae75a7a8a93ec" rel="nofollow noreferrer">a horrible Bash script</a> to rip the definition out of Kubernetes and included it via Helm templating into our CRD.</p>
