Complex jsonpath expression not supported by : CustomResourceDefinition.additionalPrinterColumns

[cmou...@redhat.com]

Hi,

Since k8s 3.11, we can customize and define the columns [1] to be used to display the result of the output of the command "kubectl get crd"

Example

apiVersion: apiextensions.k8s.io/v1beta1

kind: CustomResourceDefinition

metadata:

  name: components.component.k8s.io

spec:

  group: component.k8s.io

  version: v1alpha1

  names:

    kind: Component

    listKind: ComponentList

    plural: components

    singular: component

    shortNames:

      - cp

    # categories is a list of grouped resources the custom resource belongs to.

    categories:

      - all

  scope: Namespaced

  additionalPrinterColumns:

  - name: Runtime

    type: string

    description: "The runtime's technology/framework such as : Spring Boot, Eclipse Vert.x, ...."

    JSONPath: .spec.runtime

  - name: Version

    type: string

    description: "The version of the runtime"

    JSONPath: .spec.version

  - name: Service

    type: string

    description: "The service created from the catalog"

    JSONPath: .spec.services[0].name

  - name: Link Type

    type: string

    description: "The relation which exists between a component and a service, ..."

    JSONPath: .spec.link.kind

Result

kubectl apply -f component-link.yml && kubectl get cp

component.component.k8s.io/my-spring-boot-link created

NAME                  RUNTIME   VERSION   SERVICE   LINK TYPE   AGE

my-spring-boot-link                                 Secret      0s

Unfortunately, we can't define complex expressions as defined within the k8s's doc [2] 

  - name: Link To

    type: string

    JSONPath: "{.spec.link.kind}{.spec.link.targetcomponentname}"

The CustomResourceDefinition "components.component.k8s.io" is invalid: spec.columns[4].path: Invalid value: "'{.spec.link.kind}{.spec.link.targetcomponentname}'": must be a simple json path starting with .

Is it a limitation ? Will such complex expressions been supported in a next release ?

[1] https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions/#advanced-topics

[2] https://kubernetes.io/docs/reference/kubectl/jsonpath/

Best regards

Charles

[Clayton Coleman]

It’s a deliberate limitation right now - we are concerned with what complex expressions might cost on the server

Can you give some examples of the expressions you wanted to use?  It’s not unreasonable that we broaden the allowed set.

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[cmou...@redhat.com]

Here are an example 

type Link struct {
 Name             string
 TargetComponentName string
 Kind               string
 Ref                 string
}

Yaml example

targetcomponentname: runtime-a
kind: Secret
ref: my-postgresql-db

could be displayed with one field as such

ColumnName: "Link To"

FieldAndText: ' .spec.link.kind/.spec.link.ref ' usedBy ' .spec.link.targetcomponentname '

NAME                 RUNTIME       VERSION    SERVICE PLAN             LINK TO
runtime-a            spring-boot   1.5.16                    
service-a                                     dh-postgresql-apb/dev
link-a                                                                 'secret/my-postgresql-db' usedBy 'runtime-a'