Custom Resources with a Kind Ending in "List" are Silently Ignored

[GuyPaddock]

What happened?

If you include a custom resource in an overlay, and the Kind of the custom resource ends with the word List, it will be ignored from the output when running kustomize build. This behavior is undocumented and unexpected.

What did you expect to happen?

Custom resources should not be ignored based on the suffix of their Kind.

How can we reproduce it (as minimally and precisely as possible)?

# kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- resources.yaml

# resources.yaml - Based on https://github.com/kubernetes-sigs/kustomize/blob/master/examples/customOpenAPIschema.md.
apiVersion: example.com/v1alpha1
kind: MyResource
metadata:
  name: service
spec:
  template:
    spec:
      containers:
        - name: server
          image: server
          command: example
          ports:
            - name: grpc
              protocol: TCP
              containerPort: 8080
---
apiVersion: example.com/v1alpha1
kind: MyResourceList
metadata:
  name: service
spec:
  template:
    spec:
      containers:
        - name: server
          image: server
          command: example
          ports:
            - name: grpc
              protocol: TCP
              containerPort: 8080

Expected output

apiVersion: example.com/v1alpha1
kind: MyResource
metadata:
  name: service
  namespace: cloud-shell-dev
spec:
  template:
    spec:
      containers:
      - command: example
        image: server
        name: server
        ports:
        - containerPort: 8080
          name: grpc
          protocol: TCP
---
apiVersion: example.com/v1alpha1
kind: MyResourceList
metadata:
  name: service
  namespace: cloud-shell-dev
spec:
  template:
    spec:
      containers:
      - command: example
        image: server
        name: server
        ports:
        - containerPort: 8080
          name: grpc
          protocol: TCP

Actual output

apiVersion: example.com/v1alpha1
kind: MyResource
metadata:
  name: service
  namespace: cloud-shell-dev
spec:
  template:
    spec:
      containers:
      - command: example
        image: server
        name: server
        ports:
        - containerPort: 8080
          name: grpc
          protocol: TCP

Kustomize version

5.0.0

Operating system

Linux

[natasha41575]

I can reproduce this issue and can also confirm that just changing "MyResourceList" to something that doesn't end in "List" results in the resource being correctly rendered in the output. I find this very odd because AFAIK, we don't do any explicit filtering by resource kind 🤔

/triage accepted
/help

[k8s-ci-robot]

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In response to this:

I can reproduce this issue and can also confirm that just changing "MyResourceList" to something that doesn't end in "List" results in the resource being correctly rendered in the output. I find this very odd because AFAIK, we don't do any explicit filtering by resource kind? 🤔

/triage accepted
/help

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[cailyn-codes]

/assign

[cailyn-codes]

Hello @GuyPaddock!

After looking into this issue we have discovered that this is a result of the api-conventions, specifically they state:

Lists are collections of resources of one (usually) or more (occasionally) kinds.
The name of a list kind must end with "List". Lists have a limited set of common metadata. All lists use the required "items" field to contain the array of objects they return. Any kind that has the "items" field must be a list kind.
Most objects defined in the system should have an endpoint that returns the full set of resources, as well as zero or more endpoints that return subsets of the full list. Some objects may be singletons (the current user, the system defaults) and may not have lists.

So when kustomize is parsing the resource it will unwrap the resources in the items field. When the name of the object ends in List and there are no items it is treated an empty list.

If this does not satisfy your use case could you please provide more context about why you would like to have an object with name *List that does not have the items field?

We will add a warning when the list is empty to make this more obvious.

[haarchri]

@cailynse we running provider-kafka from crossplane eco-system and we have a resource called "AccessControlList" which is silently Ignored

[GuyPaddock]

@cailynse I believe that there is some confusion in the way that the API conventions are being interpreted. Saying that all lists must have names ending in "List" is not the same thing as saying that all things who have names ending in "List" are lists.

Similar to @cailynse, we had defined a new config entity that had a name ending in List. Ours was called an "CidrAddressList" that was a JSON object listing the CIDR addresses/ranges that were allowed to access a certain application through ingress. (It had to be an object with two properties, cidrList and cidrString rather than just a list because we needed to expose the addresses as both a comma-delimited string of values and a list of values because there's no way in Kustomize to join a list of values together with a delimiter).

As a workaround I had to change the name to CidrAddresses but that didn't have the same grokability.

[chetak123]

Hey @cailynse are you currently working on this issue ?

[cailyn-codes]

@chetak123 - I am not at the moment, there was some discussion around what the correct solution would be and then I was pulled away. Feel free to jump on it if you are interested!

[cailyn-codes]

/unassign

[meghanajangi]

I would like to work on this.
/assign

[isarns]

Any updates?
Crossplane has few resources that end with "list" that we can't deploy with kustomise.