Simulate a OpenShift cluster using CRD objects

OpenShift Kubernetes CRD

3 min read | by Jordi Prats

Openshift has some objects that doesn't exists on Kubernetes such as Project or Route. If we try to push one of these OpenShift objects into a vanilla Kubernetes we'll get an error:

$ kubectl apply -f route.yaml
error: resource mapping not found for name: "demo-route" namespace: "" from "route.yaml": no matches for kind "Route" in version "route.openshift.io/v1"
ensure CRDs are installed first

For CI/CD we might not need a fully features OpenShift cluster, just being able to push the objects might be enough, with the CRD generator we can create the needed CRDs to be able to create these OpenShift objects

We can take the object we need to create and paste it:

apiVersion: route.openshift.io/v1
kind: Route
metadata:
  name: demo-route
spec:
  host: demo.local
  to:
    kind: Service
    name: not-important
    weight: 100
  wildcardPolicy: None
  tls:
    caCertificate: "-----BEGIN CERTIFICATE-----\r\nMIIAAA\r\n-----END CERTIFICATE-----\r\n"
    certificate: "-----BEGIN CERTIFICATE-----\r\nMIIAAA\r\n-----END CERTIFICATE-----\r\n"
    insecureEdgeTerminationPolicy: Redirect
    key: "-----BEGIN RSA PRIVATE KEY-----\r\nMIIAAA\r\n-----END RSA PRIVATE KEY-----\r\n"
    termination: edge

It is going to generate a CustomResourceDefinition as follows to match this object:

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: routes.route.openshift.io
spec:
  group: route.openshift.io
  names:
    kind: Route
    plural: routes
  scope: Namespaced
  versions:
  - name: v1
    served: true
    storage: true
    schema:
      openAPIV3Schema:
        type: object
        properties:
            spec:
              type: object
              properties:
                host:
                  type: string
                to:
                  type: object
                  properties:
                    kind:
                      type: string
                    name:
                      type: string
                    weight:
                      type: integer
                wildcardPolicy:
                  type: string
                tls:
                  type: object
                  properties:
                    caCertificate:
                      type: string
                    certificate:
                      type: string
                    insecureEdgeTerminationPolicy:
                      type: string
                    key:
                      type: string
                    termination:
                      type: string

We can apply it as usual:

$ kubectl apply -f crd_route.yaml
customresourcedefinition.apiextensions.k8s.io/routes.route.openshift.io created

Once the CRD available we'll be able to create Routes as if it was an OpenShift cluster:

$ kubectl apply -f demo.yaml
route.route.openshift.io/demo-route created

Although, of course, it won't be doing anything it all since there is no controller using the CRD: We are just going to be able to add the objects but for some contexts might be more than enough.

You can find the code that translates objects into CustomResourceDefinition in GitHub: pet2cattle/python-k8s2crd, the online tool CRD generator fetches the code from this repo, using pyodine (WebAssembly) to run python code from the browser

Posted on 17/10/2022

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